The Study of Plants an Introduction to Botany and Plant Ecology

THE

STUDY OF PLANTS

AN INTRODUCTION TO

BOTANY AND PLANT ECOLOGY

T. W . WOODHEAD ,M .sc .

,P H .D .

,E .L.S .

1 1 ‘ LECTURER IN B IOLOGYAT THE TECHNICAL COLLEGE, HUDDERSFIELD

OXFORD

AT THE CLARENDON PRES S

I 9 1 5

OXFORD UNIVERSITY PRESS

LONDON EDINBURGH GLASGOW NEW YORKTORONTO MELBOURNE BOMBAYHUMPHREY M ILFORD M .A.

PUBLISHER TO THE UNIVERS ITY

7 99 0 9 1

PREFACE

THE course of work followed in this book is directed ,

in the main ,to the establishment of the fundamental

principles of P lant Physiol ogy . P lant Morphologyreceives a less extended treatment ; but this aspect

of the subject is freel y introduced in the discussion

of P lant Ecology, i . e. the relat ion of the structure

and funct i ons of plants t o their habitat . More space

has been devoted to Ecology than is usual in an ele

mentary text-book ,but the Author bel ieves that this

aspect of plant l i fe gives to field work a more defini te

aim, and broadens the outl ook of the student by linkingup Botany wi th the study of cl imate , geology, and

topography . S imilarly, to avoid the weariness of

lessons deal ing merel y with the comparis on of forms ,

the Author has throughout treated the forms of roots ,s tems

, and leaves in relat i on to their funct i ons and to

the habitat of the plant .

The plants selected for study are common species

nearl y all of them can be ob tained from the fields ,

hedgerows , and gardens , and it is expected that speci

mens wi ll be in the hands o f students using the book .

The experiments suggested are usuall y so simple and

require such inexpensive apparatus that every pupi l

in a class ought to be able to do them . Detail s of struc

ture occasionally require the compound microscope ;

where this instrument is not available , a general idea

can be obtained by the aid Of a pocket lens . I t is hoped

A 2

4 PREFACE

that the photo-micrographs and drawings in the book

will clear up any difficult ies . They have been made

specially for this book , and are designed not as sub

stitutes for actual specimens,but as ai ds to the

pract ical observat ion of plants .

Technical words have been introduced when necessary

for accurate descr ipt ion,but they have been avoided

whenever simpler terms were adequate . The common

as well as the systemat ic names of plants employed

in the book are to be found in The Botani st’

s P ocket

Book, by W . Hayward (thirteenth edit ion ,revi sed by

G . Claridge Druce . Bell ) .

Although no part icular syllabus has been followed,

the subject-matter covers the work necessary for

Matriculat i on,Senior Local Examinat ions , and the

Elementary Teacher’

s Certificate Examinat i on ; wi th

suitable omissions , the book can also be used for

Preliminary and Junior Local Examinat ions and for

Scholarship Examinat ions for entrance into Secondary

S chools .

The Author records his obligat ions to Miss M. M.

Brierley for the great care and interest which she has

taken in the preparat ion of the i llustrat ions , and for

hel p in many ways to Miss H . Rigby for s ome of the

drawings and to Mr . A. W . Sykes , Mr . W . H . S ikes,

Miss H . M. S ikes,and the late Mr . H . G . Brierley

,for

many of the photographs . To Miss D. Ventham, M.A.

,

Miss E . M. Poul ton,M.Sc .

,and especiall y to the

Rev. T. A. Jefferies , he is indebted for many

hel pful crit ici sms .

CONTENTS

PART I . THE VEGETATIVE ORGANS

CHAPTER I

THE GARDEN STOCKorgans Of a p lant ; roots , stems , leaves , flowers , fruits,seeds

CHAPTER I I

STRUCTURE AND GERMINATION OF SEEDS

(a) Dicotyledons : Bean ,P ea ,

Sunflower, Ash . Germination.

(b) Monocotyledons : Wheat,Maize ,

Oat , Onion , WildH yac inth . Germination

CHAPTER I I I

STRUCTURE OF ROOTS

Th e tissues of a root . Epidermis,root-hairs , cortex ; stele ,

vascu lar bund les, bast, cambium , and wood . Their arrangement in a young root . S tructure of Old roots cork . Roots o fMonocotyledons

CHAPTER IV

WORK OF THE ROOT

Sensitiveness of the root . Geotropism . Sensitive region of

the root . Hydrotropism . Negative heli otropism . Respiration . Regions of growth and curvature Of the root . Origin o froot-branches . Growing-region of th e stern . Root-hairs , the irstructure and use ; the root-cap . Excretion by roots . Osmosis.Water-cultures

CHAPTER V

FORMS OF ROOTS

Tap-roots and adventitious roots . Roots as storage organs .

Climbing , aerial, and aquatic roots . Suckers from roots .

Root -tubers o f th e Lesser Celand ine

PAGE

6 CONTENTS

CHAPTER VI

STRUCTURE OF THE SHOOT

The environment of the root and shoot . Dissection of a leaf .Epidermi s, stomata. skeleton, green tissue . Th e tissues of

a stem . Mechanical supporting tissues . Vascu lar bund les .

Annual rings . Cork . S eparation- layer of the leaf . Leaf -fall

CHAPTER VI I

WORK OF THE SHOOT

Sensitiveness of th e shoot . Negative geotropism . Forceexerted by the growing shoot . H eliotropism . E tiolation.

Thework of the leaf . Photosynth esis th e formation of starch .

Ch lorophyll . Functions of the vascu lar bund les . Crude sap

and elaborated sap . S torage of food

CHAPTER VIII

WORK OF THE SHOOT (CONTINUED )Transpiration . Th e P otometer. P rotection of stomata .

Wilting . Turgid ity. Root-pressure . Force of transpiration .

Air -channels in a shoot

CHAPTER IX

BUDS AND BRANCHESThe development of Shoots . The Brussels Sprout . Branch ing .

Leaf rosettes . Lilac , P rivet, Horse -Chestnut . Sycamore .

Beech . P ine . Dormant buds . S tool Shoots . Adventitiousbuds . Shedd ing of leaves and branches

CHAPTER X

PAGE

HIBERNATION ; THE STRUCTURE OF MODIFIEDSHOOTS

Annuals and Eph emerals . Biennials . P erennials . Rh izomes .

Tubers . Cor’ms . Bulbs . Contractile roots . Droppers .

E longated bu lbs . Vegetative reproduction

CHAPTER XI

MOVEMENTS AND ATTITUDES OF PLANTS

Nutation. Twining plants . Tendrils . Sun and shade positionsof leaves . P hyllodes and phylloclades . Leaf-mosaics . S leepmovements Of leaves . Movements of flowers and fruits

CONTENTS

PART II . THE REPRODUCTIVE ORGANS

CHAPTER XII

BIOLOGY OF THE FLOWER . DICOTYLEDONS

7

PAGE

I . P OLLINATION OF S IMP LE FLOWERS BY WIND AND INSECTSS tructure and functions Of the flower. S epals , petals, stamens ,carpels . Wind -pollinated flowers . S elf-pollination . Insectsas pollinators . Mouth -parts Of insects . P o llen-flowers . P erigynous and epigynous flowers th e flower-tube . Devices tosecure cross-pollination

CHAPTER XIII

BIOLOGY OF THE FLOWER (CONTINUED)II . P OLLINATION OF TUBULAR AND H IGHLY DEVELOPED FLOWERSDimorph ic , trimorph ic , and c leistogamous flowers . Irregularbee-flow ers . Summary o f th e chi ef types of flower-structurein Dicotyledons

CHAPTER KEV

BIOLOGY OF THE FLOWER (CONTINUED)'MONOCOTY LEDONS

S imple trimerous flowers . Complex irregu lar flowers of Irisand Orch is . Grass flowers . Summary o f flower -structure inMonocotyledons

CHAPTER XV

POLLINATION,FERTILI Z ATION, AND THE OR IG IN

SEEDS

Th e ch ief methods o f pollination . Nectaries . S tructure Of thepistil and ovu les . Fertilization . Changes resu lting fromfertilization

CHAPTER XVI

STRUCTURE OF FRUITS

Dry fruits : (a ) Indeh iscent : Nuts, ach enes , samaras , and

cremocarps . (b) Dehiscent : Follicles , legumes, siliquas , andcapsu les . Su ccu lent fruits Drupes , berries , pomes, and com

pound fruits

8 CONTENTS

PAGECHAPTER XVII

DISPERSAL OF FRU ITS AND SEEDS

Colonization Of a barren island by plants . Means o f dispersalby Wind , water, an imals

, and propulsive mechanisms

PART III . SYSTEMATIC BOTANY

CHAPTER XVIII

CLASS IFICATION OF PLANTS

H istory of systematic botany . The ch ief d ivisions Of Flowering P lants . The study Of a local flora

CHAPTER XIX

D ICOTYLEDONS : A . ARCH ICHLAMYDEAE

Natural orders : Salicaceae ; Betu laceae ; Fagaceae ; Ranun

cu laceae Cruc iferae Caryophyllaceae Rosaceae P apilionaceae ; Umbelliferae

CHAPTER XX

D ICOTYLEDONS : B . METACHLAMYDEAE

Natural orders : P rimu laceae ; Boraginaceae ; Labiatae ;Solanaceae Scrophu lariaceae Caprifoliaceae ; Compositae

CHAPTER XXI

MONOCOTYLEDONS

Natural orders : Gramineae ; Liliaceae AmaryllidaceaeIridaceae Orch idaceae

PART IV . COMMON TREES AND SHRUBS

CHAPTER XXII

CONE -BEAR ING TREES

S cots P ine and Larch

CHAPTER XXIII

CATKIN-BEARING TREES

Wi llow,P op lar, H azel , Birch ,

Alder,Beech

,and Oak

CONTENTS 9

PAGECHAPTER XXIV

TREES WITH MORE HIGHLY DEVELOPED FLOWERSE lm,

Rowan, Laburnum,Sycamore, Horse-Ch estnut, Common

Ash , and Li lac

PART V . ECOLOGY

CHAPTER XXVPLANT HABITATS AND COMMUNITIES

Types Of V egetation . P lant formations , associations , and

societies

CHAPTER XXV ITHE SOIL

Origin o f soils . S edentary and transported soils . Compos ition.

Organisms in the soil . P roperties . S iliceous soils . Sand , clay,subsoil, humus , and peat . Calcareous soils , liming , hoeing .

Water-supply

CHAPTER XXVIIP LANTS OF HEDGEROWS AND WALLS

Uses and d istribution o f H edgerows . P lants o f th e h edgebank ,

d itch, and sward . Trees and Shrubs . Climbing plants .

H erbaceous species . Walls

CHAPTER XXVIIIWOODLAND PLANTS

Features to observe in th e study of a wood . Dry and moistwoods on siliceous soils . Ash wood s on calcareous so ils .

P lantations . Complementary societies . Types o f . Britishwood land

CHAPTER XXIXPLANT-LIFE IN HUMUS

Abnormal modes o f nutrition . Saprophytes . Mycorrhiza and

symbiosis . P arasites . Insectivorous plants

CHAPTER XXXGRASS -LANDS : PASTURES AND MEADOWS

P astures and meadows . Grass moors . Calcareous and

neutral grass - lands . Survey o f a pasture

I o CONTENTS

P AGECHAPTER XXXI

WATER AND MARSH PLANTS

Th e vegetation of a pond . S tructural pecu liarities of waterplants . Invasion . Marsh -plants

CHAPTER XXXII

WEEDSWeeds of cornfields, meadows , and pastures

CHAPTER XXXIII

VEGETATION OF THE SEA-COAST

Seaweeds . S alt-marsh es , sand -dunes . S trand -plants . Shinglebeach es

CHAPTER XXXIVMOORLAND AND ALP INE PLANTS

Cotton -

grass moors . H eather moors . Th e Sph agnum bog .

Alpine plants

EXAMINATION PAP ERS

INDEX

PART I

THE VEGETATIVE ORGANS

CHAPTER I

THE GARDEN STOCK

WE will begin the study of plants by the examination of

a familiar example ,in order (I ) to discover its parts ;

(2) to compare the parts growing in the air with those in thesoil and (3) to notice how they are related one to the other,and thei r uses to the plant . It is necessary to describe the

s tructures methodically and in suitable terms , and to

illustrate by means of sketches all the features we have

Observed .

The several forms of Stock which are commonly culti

vated in our gardens are derived from plants growing wild

in the south of England , western Europe , the Mediterranean

region , and elsewhere .

1 Any of these will answer our

purpose, plants with single flowers being the best . One

of these is shown in Fig . I .

Vegetative organs .— Obtain a plant , exam ine it carefully,

and draw the parts you see . Two regi ons are at once

1 The plants from wh ich th e chi ef garden S tocks have beenderived by cu ltivation and selection are known to botanists as

M atthi ola incana , M . annua , and M . s inuata . P lants whi ch havecome from one parent or one kind are said to belong to one speci es .

Thus th e Queen S tock belongs to th e Spec ies i neana ; th e Tenweeks’ S tock belongs to the species annua . Both these , however,agree in many important details Of structure, and are th ereforegrouped togeth er under one genus , M atthz

'

ola . Each p lant-name

thus consists Of two words , a substantive or generic name,and

an ad jective or spec ific name . The generic name,M atthz

’

ola , was

given to the S tock by Robert Brown, in honour Of th e I talianbotanist. Mattioli ( 1 50 1

1 2 THE VEGETATIVE ORGANS

recognized : (A) a part which grows downwards into thesoil , and (B) a part which grows upwards into the ai r and is

green . The former we may call the descending axis orroot . This consists of a main tapering root called the

tap- root (often distorted in cultivated p lants) which gives

Off numerous branches growing obliquely downwards .

These in turn produce branches which arewhite , and on the

younger parts minute root-hai rs are developed . The roothairs are almost too small to be seen with the naked eye,

and are generally broken off in digging up the plant . Atthe end of each root-branch is the growing- point ; coveredby a protective root-cap . The older root-branches are

brown , being covered with a layer of cork , and are unable toabsorb water .The part of the plant above ground is the ascending

axis , and consists of organs of two kinds : (I ) a stemwhich is erect , cylindrical , strong, and somewhat woodybelow more tender, slightly ridged , and green above , with

a grey covering of branched hai rs . A tender green stem

i s said to be herbaceous . From this arise (2) thin , flatleaves (Fig . I ,f In the angle or axil between the leafand the stem, buds may be found which develop into

leafy shoots or axillary branches (b) . At the end of the

stem and of each branch is the growing-point , protected ,not as in the root by a cap , but by the overlapping youngleaves of the bud . In older plants the leaves have fallenfrom the lower part of the stem ,

leaving scars (s) on thesurface . The base or regi on Of attachment of a leaf issomewhat enlarged , and this passes imperceptibly into

the blade without a defini te leafstalk or petiole . Th e

Shape of the blade is oblong- lanceolate with an even or

entire margin and the apex is bluntly pointed or somet imes rounded . Like the stem , the leaf is covered wi thbranched hairs . Running through the leaf from base to

apex is the m idrib,which gives off a branching network of

FIG . I . THE S TOCK P LANT .—A

, the root system ; B , the shootsystem ; b, axillary branch ; f , foliage- leaf ; fl, flower ; fr , youngfru it g , ground level ; p, ped icel ; s , leaf-scar.

I 4 THE VEGETATIVE ORGANS

veins but the leaf is so fleshy that the veins are not easily

seen . Notice the arrangement of the leaves on the stemand the way in which they are related one to another .P erform the following experiment : Tie one end of

a piece of thread round the base of a leaf then wind thethread round the stem from right to left in such a way thati t touches the base of each leaf in turn as i t ascends .Eventual ly you will meet with a leaf standing vertically

above the one with which you began . Count the leavespassed by the thread , omitting the first , and determine thenumber of times the thread has passed round the stem.

Commonly you will find that the spiral goestwice round the stem and touches five

leaves ; thus we see that the leaves are

arranged spirally on the stem , and each isseparated from the one above or below i tby two-fifths of the circumference (Fig .

Exceptions to this arrangement are notuncommon In the Stock . The same testmight be applied to other plants , e . g .

FIG . 2 .

Groundsel , Oak ,Deadnettle ,

Elder ; and

D IAGRAM OF Hazel . The arrangement of leaves on a

ARRAI

NEEI

II‘IENT.

stem is called phy llotaxy.

(Gr . phy llon

leaf , tasso arrange) , and Is usually suchas to place the leaves in a favourable position withregard to sunlight .The three structures— root , stem, and leaf— are con

cerned with the growth of the plant , and are hence knownas vegetative organs .

Reproductive organs— Eventually other organs , viz .

flowers (Fig . I , fl) , appear on the upper part of the plant ,and these are concerned with reproduction .

They are produced in considerable numbers both on the

main stem and on the axillary branches . These floweringshoots form the inflorescence. Notice that in ei ther

THE GARDEN STOCK 1 5

case the flowers at the bottom are the Oldest , those next

above them are younger and so on until at the top the

youngest flowers are still in bud . Each flower arisesindependently of a leaf and is attached to the stem by

a short stalk or pedicel (Fig . I , p) . Such an inflorescence

is termed a raceme .

Examine the parts of the flower , commencing at the

outside . Remove the parts one by one and lay them out

FIG . D IS S ECTION OF A S TOCK FLOWER .— I

,V ertical section

(HT 2 , petal removed ; 3 , stamen removed ; 4 , transversesection of ovary ; 5 , pistil ; a , anth er ; cl , c law ; f , filamentg , pistil k, calyx ; l, limb ; n , nec tary ; 0 , ovary ; ou, ovu lep, petal ; pl , placenta ; r , receptacle ; re , replum s , stamen ;st, stigma sy , style .

before you SO as to show thei r interrelations . The portion

of the stalk on which these parts are borne is called thereceptacle (Fig . 3 , r) . On the outside are four erect distinctgreen leaves ; these are called sepals ,

and together form the

calyx (k) . They serve to protect the inner parts when theflower Is in bud . When the sepals of a calyx are distinctor free one from another

, the calyx is said to be polyse

palous (Gr . poly s many) . Note that two of the sepals


are bulged or saccate at the base . Now press the flower

backwards against the stem and determine whether thesetwo sepals stand right and left , i . e . are lateral with reference to the stem ; or are anterior and posterior . Thesesepals , though apparently lower, are fixed a li ttle higher onthe receptacle than the other two . Now notice the nextfour inner leaves , the petals . These, like the sepals , are

free from one another and form the corolla , which istherefore polypetalous . The petals al ternate with the

sepals and are said to be placed diagonally in the flower .Each petal (Fig . 3 , 2) consists of a long stalk , the claw (cl) ,which reaches to the top of the narrow tube formed by thesepals , then spreads out at right angles as a broad ,

white orhighly coloured , thin blade , known as the limb (l) . Furtherinwards , and higher on the receptacle, are the stamens

six stalked bodies together forming the androecium

(Gr . emer,

andros =man ,oikos = house) . Each stamen

consists of a stalk or filament (f) bearing a two-lobedyellowish body termed the anther (a) , and each lobe con

tains two parallel chambers called pollen- sacs filled with

minute bodies known as pollen-gra ins . The stamens are

not all alike : two are short and lateral in position , fixeda little lower on the receptacle than the remaining fourlonger ones , which are in two pairs , anterior and posterior .Examine the base of each short stamen and you will findon the inner side two swellings , known as nectaries (n) ,which secrete honey . The bulged sepals provide aecommodation for these . When sepals , petals , or stamens arefree from and arise below the pistil they are said to behypogynous (Gr . hypo under , gyne female) .When the stamens are removed we find in the centre

of the flower an elongated green body, the pisti l or

gynoecium (g) . All the other parts— sepals , petal s , and

stamens— stand below , i . e. are inferior to this . In otherwords , the pistil stands highest on the receptacle and is

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which forms the coat of the fruit , is called the pericarp

(Gr . pert around) .The flowers of Stocks are Often sweetly scented , especially

at night . This attracts night-flyingmoths , which visit the

flowers and search for the pollen and honey . In the processthey become dusted with pollen , and , carrying it to otherStock flowers , may deposit grains on the stigma and thus

FIG . 5 . DEHIS CENT FRUIT.

re, replum sd , seed .

secure fertilization of the ovules and the formation of seeds ,from which a new generation of plants arises .

From our study of the Stock we learn that the organs ofa plant are of two distinct kinds , (I ) vegetative organsroots , stems , and leaves— which are concerned with obtaining food and building up the main body of the plant and

(2) reproductive organs— the flowers— whose function is toproduce seed , from which arises a new generation of plants .

STRUCTURE AND GERMINATION OF SEEDS 1 9

CHAPTER I I

STRUCTURE AND GERMINATION OF SEEDS

(a ) Dicotyledons

OUR analysis of the growing Stock showed that the plant

consisted of a number of organs . We shall now Show that

these organs come into existence successively, and how

FIG . 6 . THE BEAN P OD .

— I, side view ; 2

, pod Opened along

the inner or ventral suture ; fu , funicle ; k, calyx ; p,placenta ;

st, stigma .

they perform thei r twofold function , (I ) in helping tosustain the life of the plant , and (2) in providing materials

for the growth of succeeding organs . The requisite data

are easily derived from observation and experiment .P od and seeds of the Beam— The Broad Bean provides

B 2

20 THE VEGETATIVE ORGANS

us with excellent material , and we will begin with the Beanpod (Fig . 6

,I ) . This is a frui t derived from the pistil of the

Bean flower, but , unlike the S tock frui t , it consists of only

one carpel . The parts of the pistil and some remnants of

the flower may be found . At the base is the calyx (k) , andoften parts of the stamens are to be seen . The ovary has

FIG . 7 . D IS S ECTION OF THE BEAN SEED .— I , seed with funic le

attached ; 2, end V iew o f seed ; 3 , dry seed ; 4 , partly soaked

seed 5 , concave edge of seed 6, testa showing entrance to rad icle

pocket ; 7 , rad icle pocket in side view ; 8 and 9 , cotyledons separated ;e, cotyledon fu , funicle h , hi lum ; m, micropyle ; pl , p lumu le ;

ra, rad icle r .p , rad ic le pocket t

,testa .

enlarged greatly, and now contains the seeds , or beans as wecall them , while at the tip are the remains Of the style and

stigma (st) . If we cut the pod along its upper edge and

open it we find i t is to this edge that the seeds are

attached . The seed-stalk or funicle (jet) is curious ;it grows from the edge or placenta (p) of the carpel , andi t enlarges into a much -thickened body clasping the seed .


Remove a seed (Fig . 7 , I ) . Notice that it is flattened andoval one edge is convex and the other slightly concavei t is covered oh the outside by a thick , tough , light-brown

Skin— the testa (6 t) and when the seed- stalk or funicle (fu)is removed , a scar or hilum (2 h) is left , indicating the pointof attachment . Compare this seed with a dry one (3)as supplied by the seedsman , and note the darker wrinkled

skin of the latter and the prominent dark-brown scar .Evidently such a seed has lost much water . If one of

these seeds is soaked in water, a marked change occurs .In six or seven hours the skin becomes more wrinkled

then the seed swells so much that the skin ist ightly stretched , and i f it be squeezed laterally, a li ttle

drop of water will be seen to ooze out from a small hole—the m icropyle (Gr . mikros small

,py le gate)— at one

end of the scar (2 and 5 m) . Wipe Off the water and

repeat the experiment . As we shall see later , this holerepresents the micropyle of the ovule,

through which thepollen -tube entered when fertilization took place .

Remove the skin (6 t) from the seed . Note its thick

ness ; examine the inner surface of the coat covering theconcave edge find the little pocket and determine i ts use

(6 and 7 r .p) . The structure enclosed by the skin consistsof

‘

two large fleshy lobes— the seed - leaves or cotyledonsand 9 c) , and between these is a bluntly-pointed struc

turc e radicle (8 m) , the tip being directed towardsthe micropyle . The pocket in which i t rested is calledthe radicle pocket.Separate the two cotyledons and look for the young ,curved shoot , bearing tiny leaves at i ts tip . This is the

plumule (8 pl) . Between the plumule and the radiclethick stalks are gi ven off to the cotyledons . These struc

tures— the two cotyledons,radicle ,

and plumule— forma young, dormant plantlet called the embryo .

Compare the pod and seeds of the Garden P ea or the


Sweet-Pea with those of the Bean . What are the mostimportant points of agreement or differenceF ood stored in the coty ledons

— Seeds like the Garden Peaand the Bean are common articles of food . In whatdoes the nutriment consist , and where is i t contained ?An instructive ,

though only partial , answer is easy to find .

P lace a little powdered laundry starch in a test tube ,

add water, and boil for a few minutes . Allow‘

i t to cool ,add a drop Of iodine solution ,

1and note the dark violet

FIG . 8 . FRUI T OF SUNFLOWER .—I

, side V iew ; 2,fruit Opened

and one cotyledon removed e, cotyledon fu ,funicle ; pe, peri

carp pl , plumu le ra , rad icle ; so, scar ; t, testa .

colour produced . Repeat the experiment with flour , anda S lice of potato ; the same violet coloration is seen .

This coloration indicates the presence of starch ; in otherwords , the addition Of a solution of iodine to a starchcontaining substance produces a violet coloration . Now

take a cotyledon of the Bean and place a drop of iodinesolution on i ts uninjured surface . Scratch the surface of

another cotyledon,add iodine solution to the scratched

1 A so lution Of iodine and potassium iod ide in water.

STRUCTURE AND GERMINATION OF SEEDS 23

portion , and compare the two . Repeat this experiment

with the Pea . We thus see that the cotyledons of theBean and Pea contain much starch

, and it is chiefly thiswhich gives them thei r value as food .

The seeds of the Bean and Pea agree Closely in thei r

general structure , e . g . they consist merely of a skin and

an embryo . Many seeds , however, are more complex ,

while some so- called seeds are really fru its , e . g . thoseof the Sunflower (Fig . 8

, I ) . Here we find a triangularfrui t with a narrower end , which was attached to th ereceptacle , and al so a broader end on which is a scar (so) ,left when the corolla and style dropped off . The outerribbed fruit- coat (2 pe) is hard and brittle,

and on removing

it a single seed will be found covered by a thin testa (2 t) .Such a dry , hard , one

—seeded fruit is called an achene or

nutlet. Look for the short stalk (fu) which attaches theseed to the pointed end of the fruit . Remove the seed

coat and exam ine the embryo , noting the radicle (rd ) atthe pointed end and the two flat co tyledons between

which is the small plumule (pl) . Test the cotyledonswith iodine solution : do they contain starch ? If a thin

section,treated with iodine solut ion

,is examined under the

microscope , the cells will be seen to contain a number of

small yellowish granules . These are protein or nitrogenous bodies called a leurone gra ins (simi lar granules may

also be found in the Bean ,Pea, and Potato) ; there will

also be seen many bright globules which do not stain with

the iodine solution . If,however

,a sect ion is placed for

a whi le in ether the globules dissolve also , if a drop of

I per cent . solution of osmic acid i s placed on another

section,the globules stain a blackish brown . These tests

prove that the cotyledons contain protein or aleurone

grains and much fatty oi l . Oil is a common storage

material in seeds , and often replaces starch .

Endosperm. F ood stored outside the embryo— The Ash


fru it (Fig . 9, I ) is a differen t type . Examine its curious ,slightly- twisted

,and winged fru it - case which is swollen

at one end and contains a single seed . Cut Open the fruitcoat (2 pe) and notice the mode of attachment of the

seed (2 fu) then remove the seed—coat and examinethe contents . Spl it open the seed ,

and between the twoflat lobes you wi ll find the embryo

,cons ist ing of a radicle

(2 ra) , above which are the two cotyledons (2 c) , hav mg

FIG . 9 . FRUIT OF ASH .

— I, S ide V iew 2

,fruit opened and seed

d issected c , cotyledon e, endosperm fu ,funicle pe, pericarp

ra ,rad icle t, testa .

between them a very small plumule . This seed contains

not only an embryo,but , in addition

,two large lobes (e)

stored with food -materials . Such food—reserve stored out

side the embryo is called endosperm ,and the seed is said

to be endospermous (Gr . endon within,sperma seed)

P lants s imilar to the above,which contain two cotyle

dons in the embryo ,are placed together in a large class

called Dicotyledons .

Germination . Growth of root and shoot— Let us now


and Cress on damp blott ing-paper or flannel , covering themwith a jar to keep the air around them moist , and note themode of emergence of radicle and plumule ; Observe also

FIG . I O . SEEDLING OF K IDNEY -BEAN .

g , ground level e, cotyledon .

how the cotyledons are folded,and that they come above

ground, turn green , and ,while simple in the Mustard ,

(Fig . I I,1 they are three- lobed in the Cress, a rather


unusual occurrence As the roots of these seedlings

grow they become covered with a rich crop of root -hairs

Notice carefully how they are dist ributed ,and from

what part of the root they are absent .

Seeds of the Edible Pea ,Sweet—Pea

,Vegetable Marrow

,

FIG . I I . SEEDLINGS OF MUS TARD AND CREss .— I

, section o f

Mustard -seed showing the folded cotyledons 2, 3 , 4 , and 5 , different

stages in germination Of Mustard -seed 6 , Cress seed ling ; 7 , roothair, magnified ; e, cotyledon ; a w, cell—wall e, epidermal cell ;

hy , hypocotyl n ,nucleus P , protoplasm pl, plumu le r , section

o f rad icle ra , rad icle r .h , root o hair 5 , seed s .r , secondary roott, testa .

fruits of the Sunflower , Common Ash ,Sycamore

,and Oak,

shou ld be germinated in the same way and their modes of

growth compared . In the case of the Sunflower (seeFig . note that when the radicle emerges , the fruit - coatSplit s into two halves along the edge and ,

unlike the Bean ,


the stalk below the cotyledon (hypocoty l , Fig . I I,hy )

grows in such a way as to bend in the form of a crook and ,

continu ing to elongate,carries the cotyledons and the split

fru it - coat above ground . The cotyledons now separate ,throw off

,

the fru it and seed- coats , and turn green .

Seeds of the Vegetable Marrow should be sown withtheir flat faces horizontal in a few cases cut away a thirdOf one side of the seed- coat at the micropylar end and sow

these with the cut a surface downwards, and determine themode of emergence of the plumule in each case, and note

how it separates from the seed- coat . AS the radicleemerges and turns downwards from the uninjured seeds ,a peg is formed on the under S ide

,at the base Of the hypo

cotyl, which fixes the lower edge Of the Split seed—coat -

and

holds it down . The hypocotyl above el‘ongates, the upperhalf of the seed- coat Splits off

,and the cotyledons are with

drawn and carried above ground , where they expand as

two flat,oval

, green leaves . In those cases where part ofthe seed- coat has been removed , the peg is unable to act

as holder , and the cotyledons , unable to extricate themselves , carry the seed- coat upwards

,and it is only thrown

off when the cotyledons expand . The use of the peg,

therefore , is to enable the cotyledons and plumule to freethemselves more readily from the seed- coat . The pos itionof the peg is always on the under side

,and ,

like the down

growth of the radicle,i s determined by gravity .

Two modes of germinat ion are seen in these types . Inthe Bean , Edible Pea, and Sweet—Pea ,

the seed remains

below ground and only the plumule grows into the air thismode of germination is known as hypogeal (Gr . hypobeneath , gé= earth ) . In the K idney—Bean ,

Mustard , Cress ,Sunflower, Vegetable Marrow

,Common Ash

, and Syca

more , the part of the stalk below the cotyledon (the hypocotyl) grows and carries the cotyledons and plumu letogether into the air . In these cases the cotyledons turn


green and act as the first green leaves . This mode of

germination is called epigeal (Gr . epi upon ) .Allow the seedlings to cont inue their growth ,

comparethe successive leaves as they appear

,and note that the first

formed fol iage—leaves are often S impler than the later ones .In this respect the Sweet -Pea i s an interest ing exampleto study .

Development of the Sweet-P ea .

— Sow a few seeds in soil

and allow them to grow for several weeks , supporting thetender stems with thin sticks . Note carefully each leaf

as it appears unti l the fully-matured ones are formed .

Compare the first or j uvenile foliageleaves with the later

adult leaves and try to determine the structure and uses

of the parts .As the arched shoot comes above ground (Fig . 1 3 1 , 5 ,

p . very small leaves appear the first is seen to consist

of two pieces or lobes , with a narrow pointed lobe betweenthem (Fig . 1 3 1 , 6 ,

t) the second leaf i s a little larger, andthe lobes are better developed and toothed (Fig . 1 3 1 , 7) the

third leaf st ill Shows the two lobes close to the stem and

above these is a short leafstalk, then a pair of oval lobes , between which is a slender green thread (Fig . 1 3 1 , The two

lower lobes , or stipules (st) , are outgrowths of the leaf-basethey cover and protect the rest of the leaf in the bud . The

leafstalk and blade are represented at first only by thenarrow terminal lobe in the later leaves the blade develops

two large opposite lobes , and the terminal thread becomeslonger . Finally, the terminal part of the blade divides

to form paired structures agreeing in position with thelobes of the blade,

of which they are special modifica

t ions . Note their behaviour on coming into contact with

a stick,and you will see at once the use of this curious

modificat ion as a clinging organ . In the Older plant (Fig .

1 3 1 ,1 ) these organs are well developed , and by twining

round a support enable the stems to grow up above


overshadowing plants . These clinging organs are known

as tendrils , and are of great use to plants with stems'

too

long and too slender to support themselves in an erectposition . In some plants , however , tendri ls are formed

from organs other than leaflets .

FIG . 1 2 . GRAINS OF WHEAT MAI Z E .— I , grooved surface ;

2 , convex surface of Wheat grain 3 , 4 , and 5 , stages in germi nation Of Wheat grains ; 6 , germinating grain Of Maize ; a .r , adven

ti tious roots ; em, embryo ; l , fo liage- leaves ; P l , plumu le ra ,

rad icle ; r .e, root-collar ; r .h , root-hair sh , colourless sheath .

(b) Monocotyledons

The Wheat grain . Embryo wi th one coty ledon the endo

sperm — Soak a few grains of W heat in water for a day ;

then place some of them in a jar lined with wet blotting~


paper , and others in coco -nut fibre . Compare dry and

soaked grains as to size and shape . A grain of wheat

(Fig . 1 2 ) is the product of the pistil , and is a fruit , not

a seed . The fruit - coat and the seed-coat , however , adhere

firmly, and cannot be easi ly distinguished . The outerfruit - coat , or per icarp ,

is smooth , grooved on one side

(Fig . 1 2 ,I ) and convex on the other Note the tuft of

FIG . 1 3 . VE RTICAL SECTION OF WHEAT EMBRYO .— a .r , adven

t itious root ; e, endosperm ; ep, epith elium of the scutellum ; l,

ligu le P l , plumu le ra , rad icle ; r .o, root-collar so, scutellum .

hairs at one end , and at the other an oval area in which

is a small wrinkled body (em) . Cut the grain in two alongthe groove and apply a drop of iodine solution to the cutsurface . Do all parts stain equally ? The little struc

ture at the end is unstained . This is the embryo . The

parts of which it is composed can be well made out on

examining soaked grains with the aid Of a pocket lens .


A sect ion of the embryo is shown in Fig . 1 3 . Below is the shortradicle (ra) above i s the straight p lumule (pl) . On oneside is a shield- Shaped structure

, the cotyledon or scutellum (so) , with its convex face applied to the starchy foodreserve and opposite the point of attachment of the shieldis a t iny scale, the l igule (l) .

The Wheat grain thus consists Of a fruit -coat and seed

coat fused together , an embryo consist ing of a radicle ,

a plumule,a S ingle cotyledon (the scutellum) , and a

ligule ; and , occupying the larger part of the grain , is thefood- reserve , which is outside the embryo and thereforecalled endosperm (e) . (Compare this with the fruit of the

Ash , Fig .

P lants which contain only one cotyledon in the embryo

are placed in a large class called Monocoty ledons .

Germination of Wheat and M ai ze.

—Examine germinating

grains in different stages of growth , and note the behaviour

of the parts of the embryo (Fig . 1 2 , 3 , 4 , and As the

radicle (ra) elongates,it bursts through the thick tissue

which surrounds it , and now encircles its base as a root

collar Continu ing to grow,it becomes clothed with deli

cate root-hairs (r .h) everywhere except at the tip . Lookfor the root -branches (a .r) and determine their point of

origin . Note that some Spring from the base of the stem.

Roots aris ing from the stem are called adventitious roots

(Fig . 1 2, 3 and 4 a .r) . These also bear root-hairs . Note

how the particles of fibre adhere to them and are not easily

washed Off . In Wheat the radicle does not become themainroot : the fibrous roots of the mature plant all arise fromthe nodes of the stem .

Compare the mode of emergence of the plumule (pl) withthat of the Bean and other seedlings examined , and notethe differences . In the Wheat the leaves are rolled up and

enclosed in a smooth , colourless , tui lar leaf , the wholeforming a compact structure well adapted for boring its


compared . In the Maize, note the smooth pericarp , and

the remains of the stigma as a little point above the embryo

(Fig . 1 4 ,st) , also the hard endosperm (e) . A germinating

grain is shown in Fig . 1 2 , 6 . The Oat differs from the

Wheat and Maiz e in that the grain is covered with chaffyscales . Other interest ing examples belongi ng to the sameclass are the Onion and the Wi ld Hyacinth . In these thet ip of the cotyledon remains in the endosperm and acts asa sucking or absorbing organ (see Fig . 87 , A, C ,

D) .After seeds have ripened in the fruit they commonly

require to pass through a dormant period , which varies inlength in different species , before they are able to recom

mence growth . So long as a seed is kept dry,or at a very

low temperature , growth does not take place , and some

seeds may lie dormant while retaining their vitality for verymany years but under the conditions we have provided—viz . moisture ,

air, and warmth— germination begins .

CHAPTER I I I

STRUCTURE OF ROOTS

Ti ssues of a mature di coty ledonous root.— We have seenhow roots arise,

also their form and mode of growth let us

next consider how roots are constructed . Fig . 1 5 , r i sa photo-micrograph of a cross-section of an Old root of a

Dicotyledon showing the different tissues of which it

i s composed . The outer surface i s composed of a layerof cells cal led the epidermis (e) (Gr. epi upon , dermaskin) . In the young root some of these cells grow out to

form root -hairs (see Fig . 1 1,

Beneath the epidermis is

a wide ring of cellular tissue— the cortex (Fig . I 5 , co) with

small air-spaces between the cells . The innermost layer of

STRUCTURE OF ROOTS 35

the cortex consists of closely-fitting cells with thickenings ontheir radial and outer walls . This layer is the endodermis

(Gr . endon within) . The inner tissues form the cen

tra l cy l inder or stele,and consist of a layer of delicate

cells next to the endodermis , called the peri cyc le (Gr .peri around , kyklos circle) within this are the veinsor vascular bundles , each being composed of three kinds oftissue— an outer tissue, the bast or phloem (Fig . 1 5 , b) (Gr.

phloios bark) an inner tissue, the w ood or xy lem (w)

(Gr . xy lon wood) and between the two a very del icate,

actively growing tissue, the cambium (o) .The water, which has been absorbed by the root -hairs ,

is transmitted through the cortex to the wood , and through

this conducted upwards to the stem, to which the veins go

in the form of a complicated network . Excellent skeletons

consisting of the veins of a Radish can often be Obtained

from a garden rubbish-heap .

Tissues of a y oung root. -The structure of a very young

root,however , is different (Fig . 1 5 , The bast is not

placed on the outside of the wood , i . e . collaterally, but thetwo tissues are arranged in alternating groups , i . e . radially .

The groups of first - formed or primary wood (Fig . 1 5 ,2,w

,

and Fig . 1 6 , I , 2 , 3 , p1 0 ) develop from outside inwards (theends of the rays being the oldest parts) , and by further

growth they form a solid mass of wood in the centre . In

such a root there is no pith . I t is not until a cambium ring

is formed , winding to the outside of the wood and to theinside of the bast , that the arrangement found in an old

root i s developed . Fig . 1 6 , I , 2 , 3 , makes this point clear .

S econdary growth— From the cambium and by the divi

sion of its cells to form new tissues , arises new wood to the

inside Of it (Fig . 1 6 , 2 , 3 , s .w) , and new bast to the outside

(Fig . 1 6, 2 , 3 , Sb ) ; and in this way a ring of vascular bundles

i s formed , each bundle consisting of the three tissues

bast , cambium , and wood . At first the cambium is a wavy

c 2


line (Fig . 1 6, 3 , but as growth proceeds i t becomes a

uniform ring (Fi g . 1 5 , I , o) , to the inside of which is the wood

and to the outside the bast . The root has now lost i tsradial structure and grows in thickness by additions from

the cambium in the same manner as in the stem . Final ly,a layer Of cork is formed from a ring Of cambium, the corkcambium (Fi g . 1 5 , I , c .c) , which arises in the tissues imme

diately to the outside of the bast . The cork layer thus

produced cuts Off communication between the vascular

FIG . 1 6 . D IAGRAMS ILLUS TRATING THE DEVELOPMENT OF A ROOT .

— I, very young root , sh owing alternating groups of primary wood

(P .w) and primary bas t (P .b) 2 , Older root, showing cambium (o) ,arising on th e outside of the wood and on the inside Of th e bast3 , Old root, showing a complete cambium (o) ; oo, cortex ; e, epidermis ;s .w, secondary wood , formed on th e inside of the cambium s .b,

secondary bast, formed on th e outside Of the cambium .

bundles and the cortex , and the latter dies and crumbles

away, as shown in Fig . 1 5 , 1 , co.

The l oss Of the cortex greatly reduces , for a time, the

diameter of the root , but growth goes on steadily and the

root continues to increase in thickness throughout l ife .

S tructure of amonocoty ledonous root. -The root of a Monocotyledon differs from the above in an important respect

no cambium is formed between the wood and the bast ,and when these tissues are once developed

,no further

increase in thickness can take place . The bundles of alter

nating wood and bast are also more numerous (often ten

STRUCTURE OF ROOTS 37

or more of each) the smallest and first- formed tissues of

thewood are to the outside, the later ones arewell developed ,

large, and in some species they meet and fill the centre of

the root with wood in others themiddl e is occupied bya pith .

The tissues of the root are of several kinds and modifiedto serve Special purposes the root -hairs absorb from th e

soil water which is passed through the cortex to the wood ,and the latter conducts i t upwards to the Shoots . The

organic food, which, as we shal l see later , is formed in theleaves , i s conducted by the bast and neighbouring delicate

tissues to the growing organs and storage -tissues .

CHAPTER IV

WORK OF THE ROOT

IN our Study Of germinat ing seeds we found that theroot was the first organ to be formed , and that i ts appearance was followed by the emergence of the young Shoot .What is the future of such a root How does i t grow ?Of what special use is i t to the plant How does i t do i ts

work ? A few experiments and Observations wil l help us

to answer these questions .Di rection of growth of root and shoot.— In a pot of fibre

Or soil , sow three soaked Bean seeds , one with the radiclepointing downwards , another horizontally , and a thirdupwards . After a few days examine them . In what

directions have - the radicle and plumule grown in each ?

(Fig . 1 7 , I , 2, We observe that the radicle endeavours

to grow downwards into the dark , moist soil,independently

of the position in which the seed was placed in the ground,


and that the plumule just as persistently grows upwards

into the air and sunlight .

The stimulus of gravi ty . Geotrop ism.

—What force is atwork which determines these directions of growth ? I f agrowing seedling is placed on its side and attached to a rod

which is caused to revolve horizontally by means of clockwork (Fig . the radicle and plumule will continue to growin that direct ion . An instrument constructed for the pur

pose of rotating plants in various positions is called a

FIG . 1 7 . SEEDS OF BROAD BEAN S OWN IN D IFFERENT P OS I TIONS .

In each case th e rad icle grows downwards .

klinostat . 1 Further, if seedlings of the Pea are pinned ona vertical disk with their roots pointing towards the centre,and the disk is then revolved rapidly for four or five hours ,the growing roots turn outwards away from the centre ofrotation , and the plumules turn inwards towards the centre.

In this experiment the seedlings have grown under theinfluence of a force stronger than the attraction of gravity .

The influence of centri fugal force affects the radicle and

1 A simple form of klinostat may be made from a small c lockby removing th e hands and fix ing a sh ort tube to th e axle of the

minu te-hand . Fit up a ligh t bottle as a moist chamber and borea hole in th e cork, into whi ch th e tubemay be firmly fitted . Seed

li ngs pinned to the cork may be rotated as in th e experimentdescribed .


adjust itsel f to the changing conditions . The power ofresponse and adjustment is the most characteristic feature

of l ife , and i t i s important that we should pursue the

subj ect a li ttle further .Contact stimulus — In an ordinary soil

,it will commonly

happen that roots will meet with obstructions , such as

stones . Under these circumstances , how will they behave

Take a wide-mouthed bottle, half-fil led with stones or frag

ments Of broken plant pots , moistened with a l ittle water .Then attach two or three seedlings to the cork ,

and suspendthem with the radicles directed downwards into the bottle .

Notice what happens as they come into contact with thehard fragments . The roots turn away

, escaping the injurywhi ch would result i f the tip were forced against a sol id

Obj ect .

The sensory region of the root — This shows that some part

of the root must be sensitive,and the following experiments

determi ne the sensory region of the root .Take four seedl ings Of the Broad Bean (a to d) with

radicles about I 3 inches long , and treat them as follows1 . P lace seedling a horizontally on moist coco-nut fibre.

2 . Take a razor and cut Off one-sixteenth Of an inch fromthe tip of the radicle of seedling b and place it alongside a .

3 . P lace seedl ing o, uninjured , on i ts S ide for an hour,

then cut Off the tip as inb and lay it horizontally on the

moist fibre .

4 . P lace seedl ing d on i ts side for a day until i ts tip hascurved downwards , then cut off the tip as with b and 0

,

but place the seedling with the root pointing downwards .Allow the seedlings to grow and carefully compare theresults .

a turns downwards ; b grows , but does not bend c bendsas i n a d does not turn downwards, but continues to growhorizontally .

If the seedlings are allowed to grow under favourable

WORK OF THE ROOT 4:

conditions a new tip is formed and grows downwards asin an uninj ured root . We thus see that , though able togrow in length , seedlings b, c , and d had lost their sensitive

ness, and that the last one- sixteenth of an inch includes

the region which is able to receive and respond to a

stimulus . This is known as the sensory reg ion Of the root .

The stimulus of water. Hydrotropi sm.

—TO pursue the

subj ect of root sensitiveness further , perform the following

experiment . Obtain a shal low box,remove the bottom ,

and replace i t by wire gauze (Fig . Fill the box with

wet coco—nut fibre and sow in it a number of peas . Tilt

FIG . 1 9 . EXPE RIMENT TO SHOW THAT ROOTS ARE S ENS ITIVETO THE S TIMULUS OF WATER .

the box at an angle of 45°and protect the bottom from

strong light . As the seeds germinate , the roots , owing tothe shallowness of the box , soon grow through the gauze

into the air . Note the behaviour of these roots . We see

that they cling to the surface and may even bend backand grow upwards into the wet fibre . From previousexperiments we should expect the roots to grow vertically

downwards in response to the stimulus of gravity . What

other force i s now Operating to draw the roots away from

the vertical direction We see that the attraction of wateris , under these circumstances , more powerfu l than that of

gravity . This tendency of roots to turn towards or be


attracted by water is called hydrotropism (Gr . hydorwater) . Roots are att racted to , and grow best in , the

moist layers of the so il and the roots of trees and shrubsmay be drawn cons iderable distances in the direction o f

a suitable water- supply . A dry soil retards root growth .

In this connexion i t is interesting to note how the

distribution of roots below ground is related to the shoot

system above ground . The leaves of some plants are SO

placed on the stem that drops of rain falling on them are

directed towards the stem the drainage from the leaves,therefore, i s concentrated on that part of the groundimmediately round the stem . Such plants have commonlya long tap- root but no widespreading root-branches . Ino ther cases the leaves are so arranged as to throw the waterfrom thei r tips and the water falls over a larger circle tothe outside of the plant . The watershed of such a plantis therefore a large one

, and on examining i ts root—systemwe find that the young absorbing branches spread extensively , and collect water from a corresponding area .

The stimulus of“

light. H eli otropi sm.

— If we observe the

roots of the Ivy we shall find that they very generallyturn towards the surface along which the plant is growing .

This will commonly be the moister surface,and hence we

have a case of hydrotropism . But i t i s equally true thatthey are growing towards the shady S ide and away fromthe light . That roots can be tempted to grow from the

usually exposed surface of the Ivy stem can be shown bythe S imple experiment of keeping a portion covered witha wet cloth ; the roots wi ll soon be seen to grow underthe cloth .

Suppose, however , that seedlings are grown on gauzeover a jar of water so that the roots hang downwardsinto the water . If we now exclude l ight from the jar at

every point except a narrow sl i t on one side, throughwhich a strong light can be admitted , the growing roots

WORK OF THE ROOT 43

will turn away from the light towards the shadedside . Thus Ivy roots are probably not merely growing

towards the moist surface ,but also away from the sunv

light . The sensitiveness of growing organs to sunlight

i s termed heliotropism (Gr . heli os sun) , but as rootsusually turn away from, and not towards

, the lightthey are said to be negativelyheliotropic .

Our experiments have shown

that roots are sensitive to a

number of different stimuli ,namely

,gravity , contact , water ,

and light , and tha t in responseto these stimu li roots grow ina definite manner . We wi ll nowdetermine the important fact

that root s are sensitive only inthe presence of oxygen .

Necessi ty for. oxygen— Take

a wide-mouthed bottle fittedwi th a good cork or stopper ,and fill half of it wi th water that FI G . 2 0 . EXPE RIMENT Tohas been boiled so as to expel snow THAT THE ROOT I S

the dissolved ai r . Select two NOT SENS ITIVE.

IN THE AB

seedlings of the P ea wi th radi clesSENCF °

,

F O’fYGEN '

f a ’

seedhng In bo i led water ;about an Inch long . Take a board b, seed ling in air .

(which has been previouslyboiledto destroy mould- Spores) and pin the seedlings to i t in

such a way that the radicles are directed horizontallyas i n Fig . 2 0 . P lace them in the bottle, submergingone in the water (a) , and placing the other well abovethe water in the air (b) ; then close the bottle witha stopper . Ensure that both seedlings have thei r radiclesdirected downwards and place them hori zontally onlywhen putting them into the . bottle . Leave them for


a few days and note what happens . The one in the

air has turned downwards , as we Should expect from

our previous experiment , but the one in airless water

has continued to grow in the direction in which i t

was placed‘

in the water . . In other words , the root

only possesses this power of turning when supplied with

air containing oxygen . This suggests a further question .

Do plants utilize the oxygen of the air in the ordinary

process o f growth ?Respiration .

— A S Imple experiment will enable us to

understand the important rOle played by plants in changing

the composition of the air . Soak a number of peas inwater for a day , and then place them in two j ars (A and B)lined with wet blott ing-paper . Put on the stoppers and

keep them on for a day or two . A similar jar may be

prepared,but without peas

,for comparison . Then test the

air in the j ars as follows : (a) insert a lighted taper,and note whether the air in the jar containing the peaswill now support combustion ; (b) pour in a little lime

water and note the result . From these tests we see thatthe germinating peas have

'

removed from the air the gas

which supports combustion,viz . oxygen , and have given up

to the air a gas which turns lime-water milky, viz . carbon

dioxide. I f we breathe on to lime-water we observe a

S imilar effect . In other words,P eas , during thei r growth ,

are using up oxygen and giving off carbon di oxide, j ust as

we arewhen breathing . This process , which is called respiration , i s necessary to the existence of plants theywould soondie if kept wet in a closed bottle and withou t air .

The oxygen taken into the tissues of the plant duringrespiration acts chemically upon the complex o rganic substances which consti tute the plant , with the result

‘

that

they are converted into simpler compounds such as carbondioxide and water . During these changes energy is setfree, and thus the work necessary to the li fe of the plant

WORK OF THE ROOT 45

is performed . Some of this energy appears as heat which

helps to maintain a suitable temperature within the livingtissues Of the plant .

In describing the Stock we spoke of the growing-points

of root and stem. The root in pushing its way through thesoil meets With much resistance, but is protected at the

tip by a root -cap , the end Of which is constantly dyingand wearing

‘

away , to be re

placed by new tissue . On th e

o ther hand the stem- tip has no

cap , but Is protected by’

the

Overlapping leaves which form

the end bud .

Growing-regi on of theroot— It

will be interesting to compare

the manner of growth of rootand stem and to determine

experimentally the mode of

e longation in each case .

Select a germinating Bean FIG . 2 1 . BEAN SEEDLINGwith a radicle about an inch MARKED TO DE TERM INE THE

long, W ipe Off adhering parREGION OF ELONGATION IN

ticles taking care not to injureTHE Ra m— L at th e com

.

”

mencement Of the expen

the Bean in any Way” and ment ; 2,at th e end of 30 -3

mark about a dozen lines across hours .

i t in Indian ink . This can bedone as follows : Take a piece of cotton thread and

hold it by both ends bend i t , and dip the middle Of

the thread into the Ink . Then lay i t across the root

so as to make a Clear transverse mark . Begin quite

at the tip and make a series of marks about Tl

ginch

apart backwards from the tip . Obtain a large , wide

mouthed bottle or jar fitted with a cork (Fig.

Line i t with blotting paper so that the lower edge dips

into about half an inch of water ; this provides a mois t


chamber in which to grow the seedling. Push a large pinthrough the cork and fix the Bean seed firmly to the pointthen replace the cork in such a way that the markedradicle hangs downwards Within the bottle SO as to avoidtouching the sides . Make a sketch of the radicle at the

commencement of the experiment , showing the exactnumber of lines and their distance apart , and at the end

Of two or three days make another Sketch and note whathas happened (Fig. 2 1 , Has the root grown ? Count thelines and compare them with the original Sketch . Whatis their position now ? Which lines are most widely

separated ? What changes have occurred in some of thelines ? Has elongation occurred at the extreme tip , or isthe position of the first line still unchanged We Observethat the extreme tip (the end of the root- cap) has notgrown , but that elongation has been most active in theregion immediately behind this and included within thenext two or three l ines , which , as the root has elongated ,

have been drawn out and now appear as a number o f

dots .Region of curvature — Mark the radicle of another Bean

seedling and place i t in a moist chamber as before, butfix i t with the radicle horizontal . Allow i t to grow , and

note where curvature takes place . Observe that the regi onsof curvature and elongation coincide and are includedwithin the last quarter of an inch , but the sensory region

(p . 40 ) is confined to the last sixteenth Of an inch of the

root- tip .

If the experiments have been carried out successfully,

the seedlings may be used for observing the manner in

which the branch roots emerge. Replace the seedlings and

al low them to grow a few days longer. Note that they

come out in four, sometimes five, vertical rows that they

are not in any way related to leaves , and grow out obliquely

from the radicle . In cases where the radicle has been


Absorption by Roots

Root-hairs the organs of absorption — If young roots ,bearing root-hairs , are exammed by means of a pock et lensor under a microscope , i t wi ll be seen that each root -hairconsists of a long, tubular outgrowth of an epidermal cell

(see Fig . I I , 7 , e) . The wall (o.w) consists of a thin mem

brane of cellulose, the substance of which the fibres ofcotton are composed . The outer exposed surface is somewhat slimy , and to this the soil—particles adhere firmly .

Within the tube is the living substance known as protoplasm (p) , together with a little rounded body— the nucleus

(n) . The protoplasm forms a thin living lining to the tubeand from the lining

,strands of protoplasm stretch across

the cavity . The centre of the tube is occupied by sap .

Farther back ,in the older parts of the root

, the surfaceti ssues are corky and no root -hairs are found . Root -hai rs

are also absent from the region protected by the root—cap .

That part of the young root which bears root-hairs is called

the root -hair region .

The different regions of a root are strikingly Shown ina plant which a gardener would describe as pot—bound

i . e . a plant which has grown so long in a pot that its rootshave spread themselves out in a tangled mat between thesoil and the pot . On turning out such a plant numerous

tender, white roots , crowded with root-hairs , are found

covering the surface while the roots buried in the soi l

are tough , wiry, and covered with a firm brown layer ofcork .

What are the uses of these different parts ? The root

cap doubtless serves to protect the young growing root asi t pushes i ts way through the soil . The older parts , surrounded and protected by cork , are no longer able to

absorb water , but they fix the -plant in the soil and bear

at the ends of their branches the tender roots clothed with

WORK OF THE ROOT 49

root -hairs . We will determine the important function of

the root -hair region with the help Of a few experiments .

Acids excreted by roots — Obtain a piece of polishedmarble ,place i t in the bottom of a shallow box ,

and cover i t two

to three inches deep with fine wet sand . In this,place

a few seeds of Sunflower, allow them to germinate , and

in ten to twelve days examine the seedlings , noting how

the roots , unable to descend vertically , have spread over

the marble slab . Now examine the surface of the slab and

see the change that has taken place wherever the roots of

the seedlings have touched i t . The tracks of the roots areClearly marked by the corrosion of the polished surface .

NOW take a l i ttle dilute hydrochloric acid , dip into it

a small camel-hai r brush,and write the date of the experi

ment on the polished surface. When this is dry it wi ll be

seen that the course taken by the brush is etched on the

surface,just as was the course taken by the roots . A small

piece Of cotton thread dipped in the acid and laid on the

slab will S imilarly leave i ts trail . Can i t be that the youngroots and thei r root -hairs during thei r active growth excrete

a substance capable of etching marble They do ,for we

have already seen (p . 44) that germinating seeds give off

much carbon dioxide , and this gas in the presence Of water

is able to dissolve marble . It is probable that young roots

are able to excrete other acids capable of dissolving mineralsubstances in the soil . Thus they may bring into solutionsubstances otherwise difficult to dissolve ,

and these may

be absorbed as food by the plant .

Wi lting .

— Allow a plant growing in a flower-pot t o

remain unwatered for a few days , and note what happens .

Now water the soil and notice what changes take place .

Obtain a young, leafy shoot Of Laburnum and notice howsoon the leaves droop . P lace the cut end in water , cut

Off a small piece (under water) , and note how quickly theshoot revives . We see that , as the soi l loses water, the

1 996 D


shoots above ground droop or wilt but on renewing the

water- supply they become turgid , i . e . the tissues absorbwater . The leaves expand and once more become firm .

Water is essential to enable a plant to maintain i ts firmness .

FIG . 2 3 . OSMOS I S EXPE R IMENT .

a , th istle funnel containing sugar solution ; b, jar Of water .

Osmosis

Osmosis is a natural process which has an importantbearing on the work Of roots . We shall best understandi t by means Of the following experiment . Obtain a thistlefunnel and wi th a piece of moistened parchment paperclose the mou th Of i t as in Fig . 23 . Tie the paper firmlyround the rim and seal the junction carefully with vaseline

,

paraffin,or plasticine . Fill the bulb of the funnel with

a strong sugar solution and suspend it in a jar of water .

WORK OF THE ROOT 5 1

At definite periods of time mark the height of the risingcolumn by means of narrow strips of gummed paper . If

the solution is sufficiently strong ,the liquid wi ll rise con

si derably ,and it will be interesting to increase the length

of the tube and determine how high a column can be raised .

This can easily be done by connect ing a long piece of glasstubing to the funnel by means of a piece of rubber tub ing .

Consider the conditions of the experiment . In the bulb

of the funnel is a dense solution separated from a weak

solut ion by a permeable membrane . Under these con

ditions an exchange takes place ,but , as we see from the

experiment , a very unequal one . On the one hand, the

water passes quickly through the membrane,diluting the

sugar solut ion ,whi lst

,on the other

,the sugar solution

passes slowly into the water . If this exchange goes on ,

the two solutions will in time become equal in density .

The passage of l iqu ids of different densit ies through a per

meable membrane which origi nally separated them is called

osmosis .

Let us now compare the condit ions of the roots in thesoi l with those of their counterpart in this experiment .The root -hairs may be regarded as corresponding to theclosed funnels , thei r contents a dense solution , and their

walls permeable membranes . The soi l—water will now be

the weak solution separated from the dense solution withinthe roothair by (1 ) the outer slimy or muci lagi nou s layer

which readi ly absorbs the soi l-water, (2 ) the permeable

cellu lose wall,and (3) a very thin lining layer Of the living

protoplasm known as the plasmatic membrane,which

,

unlike the parchment membrane, can determine what substances shall enter or leave the cell . From such a com

parison we are able to Obtain some idea as to how water

is t aken up by the root -hairs and passed on to the innert issues of the plant . The process

,however

,i s extremely

complicated , partly owing to the complex nature of the

D 2


cell- contents and the selective power of the plasmaticmembranes .Each of the fine par ticles of which the soi l is composedis coated with a thin film of water containing mineral saltsin solution . The root -hairs press against and become

moulded to the particles , and water (together with a selection of the d issolved mineral salt s) i s drawn into the roothair . This continues as long as the osmot ic attract ion of

the cell- contents can overcome the surface tension of the

film of water surrounding the soil-particle . If water i srenewed from adjacent particles absorption will continue :i f not , the plant will be unable to obtain a sufficient supply

,

and the effect on the plant will be seen by the drooping

of the leaves .

Turgidi ty .

— When a plant is dug up and transplanted it

Wilts , but after a time recovers . Why does it wilt What

changes take place that enable it to recover ? We haveseen how very small and tender the root -hairs are and how

easi lv injured , and we have noticed also their great importance as absorbing organs . The movement of the soi l ind igging up and transplanting will obviously break off a largenumber of these hairs and so reduce the absorbing power

of the root , hence wilt ing will occur . New root -hairs,

however , are gradually formed , which absorb water and

soon bring the plant back again to it s fresh condit ion .

The condition of l iving cells , whereby their elast ic walls

are stretched by the pressure of internal fluids , is called

turgi di ty . The freshness Of a shoot depends upon its

turgidity loss of turgidity is the cause of wi lting .

P otato osmometer .

—Another experiment will enable usto real ize how the water taken up by the root -hairs may

travel through the outer to the inner t issues of the root .Obtain two long and similar potatoes with uninjured skins .Boil one of these for fifteen minutes and allow i t to cool .Then prepare both the boiled and the unboiled potatoes

WORK OF THE ROOT 53

as follows (Fig . 24) Cut a slice from one end so that eachpotato will stand upright , and pare from this end a ring of

skin to the height of three-quarters of an inch . Cut a slice

from the other end of each potato , and bore a hole an inch

in diameter through the middle nearly to the lower end .

Fill half of this hole with sugar and add a little water to

moisten it . Now stand each potato upright in a dish con ‘

taining sufficient water to cover the peeled surface . P lace

the two dishes side by side and allow them to stand for

two or three hours ; then compare them . In the living

(unboiled) potato the liquid rises

steadily in the cavity and eventually

runs over the margin . The dense

sugar solution has withdrawn water

from the cells lining the cavity, thesap of these cells thereby becomingconcentrated . These cells now with

draw water from those farther

outwards and this is repeatedFIG 24 P OTATO

until the cells of the pared surfaceOSMOME TER.

— a , cavityoutside

,which draw water from the in potato containing

dish,are reached . Very different i s sugar ; b. d ish o f water .

the behaviour of the cells of the

other potato , which have been killed by boiling . Compare

the amount of water absorbed in the two cases and the

difference in leve l of the liquid in the two cavities . In theliving potato the liqu id rises in the tube and eventually

overflows, in the other exchange is very slow indeed . This

will help us to realize the act ivity of living tissues in

taking up and transmitting water, as compared with theaction of a dead tissue .

We are now in a position to understand the importanceof root -hairs to a plant . The root—hair region , togetherwi th the younger part of the root which has not yet formed

root -hairs , is the special organ for the absorption of water .

4


The root -hairs are often of considerable length, and theirform and number very greatly affect the absorbing powerof a plant , e . g . the root-hairs of Maize increase the surfaceof the root five and a half times ; wh ile those of Barleyincrease the surface twelve times . In some plants withvery small leaves (e . g . Heaths) few or no root -hairs are

formed ; and in many water- plants they are absent or

nearly so ,for these plants are able to absorb water through

the general surface of the epidermis, not only Of the root

but often of the shoot as well ; but most plants dependfor their supply of water and mineral food on the absorb ingactivity of the root—hair region .

The Food absorbed by a Root

S oi l- organi sms and their work — Ordinarily the soi l inwhich the roots o f plants grow is a very complex mixtureof substances— sol id , l iqu id , and gaseous ; inorganic and

organic living and dead animal and vegetable . Myriadsof tiny organ isms find a home there, and also bigger onessuch as earthworms and the larvae of many insects . Thesefeed upon the l iving and dead materials in the soil , reducingthem into simpler compounds

,breaking the soil itself into

a finely divided state,so that eventually a number of sub

stances are brought into solution which are essential to thefood of a green plant . The organisms , however , differmuch in their usefulness in this respect earthworms aregreat ploughers and pulverizers of the soil

,and mi nute

organisms , like bacteria,are valuable or even indispensable

but others prey upon them and ,by reducing their numbers

and therefore their usefulness , retard the format ion of

soluble food-materials , thus rendering more and moredifficult the sustenance of plants . But these foes in turnare checked by others

,and so this complex society of inter

dependent and ever- changing members is act ively at workreduc ing the complex materials and preparing from them


FIG . 2 5 . WATE R - CU LTURE S OF BUCKWHEAT (P fe ffer) .a with ou t potassium ; b, normal solution o

,with out iron ; d , co

verSp lit to receive th e plant stem g , jar containing cu lture so lution .

WORK OF THE ROOT 5 7

In order to show the importance of the variou s con

stituents, plants Should be grown in the following incom

plete culture solutions and the results compared : ( 1 ) Cul

ture solution without potassium n itrate (Fig . 25 , a) , (2)without magnesium su lphate , (3) without calcium phos

phate, and (4) without ferric chloride (Fig 25 , o) .

It wi ll be interesting to carry out such experiments , but

as the resu lt s are Often very variable and contradictory , it

is well to try several of each and express the average resultsby means of curves . The j ars containing the food solut ions should be covered with opaque paper in order to

exclude light , and the solut ions should be renewed at least

once a fortnight and the vessels thoroughly cleaned and

sterilized with boiling water , as Algae and other organisms

are liable to develop in them . The plant may be sup

ported by a split cork (d) , as Shown in the figure . Keep the

cork and the part of the stern passing through it dry ,

otherwise it may be attacked by Fungi and decay .

Analyses of plants show that a number of substances

are commonly present which water- cu lture experimentsprove to be non - essent ial . S il ica

,which is present in large

quantities in Grasses , Horseta i ls , &c .,i s one of these .

Chlorine also is necessary to only a very few species . On

the other hand ,i f potassium compounds or n itrates are

omi tted , the plant su ffers . If iron is omitted , chlorophyll

i s not developed , and the leaves are sickly yellow in colour

(Fig . 25 , o) . By means of water- cu lture experiments we

learn that the food of a green plant must contain the

following elements oxygen , hydrogen , n itrogen , calcium ,

magnesium, potassium ,phosphorus , sulphur , and iron ; all

of which a plant obtains in solution from the soi l . One

important element , carbon ,forms about half the dry weight

of a plant , yet is not present in a cu lture solution ,nor is the

plant able to obtain it from the soil . The question therefore arises— How does a plant obtain the carbon which


forms so large a proport ion of its substance ? But thisi s a question we cannot answer unti l we come to the workof leaves .

From the above observations we learn that in manyplants roots arise from the radicle which grows downwards

as the tap- root

,e . g . Bean ,

Pea , Oak . In others,e . g . Wheat

and most Grasses, the radicle soon dies and i s replaced by

advent itious roots from the stem . Roots fix the plant inthe soi l and absorb weak solutions of mineral salts ; theabsorbing area being increased by branching and to a

greater extent by root—hairs . Usually ,roots contain no

chlorophyll and bear no leaves , therefore the branches arenot axillary . In a young root , the groups of wood and

bast alternate with each other,and the first - formed wood

develops towards the centre (i . e . centripetally) . From cellso f the pericycle and oppos ite the groups of primary wood ,

branch roots arise in vert ical rows . The t ip of each rootis protected by a root - cap and possesses a sensory regionwhich is able to perceive a st imu lu s and transmit an impulseto the neighbou ring t issue ,

where growth occurs . The root

is sensit ive only in the presence of oxygen . The directionof growth is determined by the nature of the st imu lus ,i . e . towards the soil

,water, and food ; and away from

obstacles and light . Some roots , swollen with a largecellu lar t issue

,store much starch ,

sugar , inulin , and other

reserves of food . Some of these we will now consider .

CHAPTER V

FORMS OF ROOTS

WE have seen that in D icotyledons (e . g . Bean , Pea , and

Stock) the radic le of the embryo grows downwards and

becomes the primary root of the plant . From the tap—root ,

branches or secondary roots arise which in turn give off

FORMS OF ROOTS 59

numerous branching fibres . In Wheat , Oat , Maize, rootsare developed not as branches of the radicle, but from the

stem . The rad icle is usually short - lived , and the roots areall similar and slender

,and known asfibrous roots (Fig . 26 ,

As they are developed from some part of the plant

FIG . 2 6 . ABNORMAL FORMS OF ROOTS — I, conical

root o f Carrot ; 2, spindle-shaped root Of R ad ish ; 3 ,

globular root of Turnip ; 4 , fibrous roots of Grass ;5 , plant of Duckweed ; P

, flattened leaf- like stem ;

r , root ; r .p, root-pocket .

other than the radicle and i ts branches , they are known as

adventi tious roots,and in Monocotyledons they are the most

common kind .

S torage, climbing ,and aquati c roots — In exceptional

cases (Fig . 26,1 — 3 ) roots thicken considerably . The tap

root becomes conical in the Carrot and Beet , and sp indleshaped and sometimes globular in the Radish . The Lesser


Celandine (Fig . 28) and Dahlia have swollen or tuberous

roots . Such Swollen roots serve as important food-storesfor the plant

,and some of them , if tested with iodine solu

t ion,will be found to contain much starch . Others , like

Beet,contain cane sugar, and the Dahlia contains an allied

substance called inulin . Frequent ly plants produce root s of

more than one kind and serving different funct ions , ( 1 ) some

being fibrous, absorbing roots (2 ) others swollen and stored

with food (e . g . Lesser Celandine and Dahlia) . Some have

roots which after greatly elongating, contract and pull the

stem down deeper into the ground , e . g . Dandelion , Crocus

(Fig . Bluebell (Fig . The adventitious roots of theIvy

,which arise in clusters on the aerial stems, serve rather

as holdfast s and climbing organs than for the purpose of

absorpt ion . The roots of some water-plants like the Duckweed (Lemna) (Fig . 26, 5) and Frog-bit (Hydrochari s) danglein the water, from which they absorb nutriment

,and do not

enter the soil . They are truly aquatic . Those of some

tropical aquatic plants contain large air-spaces and serveas floats .Aerial roots .

—Roots,though rarely green , do sometimes

develop the green colour characteris tic of leaves,as in the

roots of a few water -plants such as the Duckweed,and in

the aerial roots of Orchids . Many tropical Orchids, growing

perched on the trunks of trees,produce roots of three kinds

(I ) holdfasts , which fix the plant like a bracket to the tree

(2 ) long aerial roots which hang down in , and absorb mois

ture from,the air ; and (3) nutritive roots , which grow

among,and absorb substances from

, the humus that collectson the bracket of leaves .

Adventi tious shoots : suckers - One of the most constant

characterist ics of roots is that they give rise to members

s imilar to themselves , viz . root-branches . Thus they di ffer°

from stems,which produce members unl ike themselves

,

viz . leaves , which are usually green . It often happens ,

FORMS OF ROOTS 6 1

however,that roots give rise to leafy shoots . Familiar

examples are Dock and Dandelion . If,i n at tempting to

erad icate these from a lawn we cut the plants so as to leave

FIG . 2 7 . P LANT OF RAS P BERRY,bearing a sucker (s )

on i ts root (r ) .

part of the tap- root in the ground,leafy shoots eventually

spring from the buried portion of the root . In the caseof the Dandelion

,often five or S ix shoots

,each bearing a

rosette of leaves,will appear in the place of the part we


have removed . Such shoots are called adventi tious shoots .

Some shrubs and trees often produce adventitious shootsfrom horizontal root-branches ,

e . g . Raspberry (Fig .

Rose,Bramble

,Hawthorn , P oplar, and Hazel . Shoot s

aris ing in this manner from roots are called suckers .

Roots vary greatly in thei r duration they may be

annual, a fresh crop being produced each season biennial ,

l iving two years only or perennial,living for many years .

Even among perennials , some roots , such as those of bulbsand corms , often live only one season ; the bulb of one

season dying away and leaving an offshoot or bud to continue growth whi ch forms roots of i ts own .

Tuberous roots of Lesser Celandine.

— The Lesser Celan

dine has roots which Show some specially interest ingfeatures . The plant flowers in the early spring . Some

times i t grows in open,sunny places and receives frequent

visi ts from insects,but often in wet , shady hollows in woods ,

where insects are scarce and fewer seeds are set . The

plants growing under such conditions should be carefully

stud ied . We have already seen (p . 60 ) that this plantproduces two kinds of roots (Fig . From what part ofthe plant do the tubers spring How do they grow How

is the compact cluster of tubers formed Of what uses arethe tubers to the plant

Take a few seedlings (Fig . 28 ,2 , 3 , 4) and note the coloured

scale (so) at the base and the small green foliage- leaf . Inthe axi l of the scale a tuber (t) is formed , wh ich bursts

through i t and grows parallel to the root (r) . Later,a

young shoot elongates , uses up the food- reserves in thetuber , and forms one or more leaves (Z) . In the axils of theseleaves new tubers develop

,and may Often be found to elon~

gate and turn sharply over the edge of the Sheathing-baseon thei r way to the soil ( 1 , t) . Examine them closely

, and

note that they are clothed with root-hairs,especially when

growing in damp air . If a transverse section is examined,


Such axillary tubers occur commonly on the older plantsand , as the other parts decay, the tubers fall to the ground ,and in t ime produce new plants from the buds which ariseat their base . Two or three tubers may arise at a node

,

and when several leaves are produced c lose together a largecluster of tubers results .

Fig . 28 , I , shows tubers springing from three successivenodes . By the elongation of the tubers they may enterthe soil and become independently rooted . The decay ofthe internodes at the end of the season will result in several

independent plants . This mode of origin of roots at the

nodes ,and the formation of new plants by vegetat ive

means , is of common occurrence .

CHAPTER V I

STRUCTURE OF THE SHOOT

Environment of the root and shoot. -The envi ronment ofthe Shoot is totally different from that of the root . In thesoil the root is surrounded by a moist medium

,and is in

the dark . It is less exposed than the shoot to dryi ng winds

or heavy rain , t o biting cold or the bright rays of th e sun,

to the heat of the day or the chills of the night . The con

ditions of life below ground are,on the whole,

more uniform ,

and the parts are not exposed to such sudden and oftenextreme changes as are those parts growing above ground .

For healthy existence,thei r form and structure must be

adapted,not only to withstand

,but to make the best use

of,these condi tions . We have ,

therefore ,to regard the

Shoot of a plant from these di fferent points of view .

As we have seen in the Stock ,the stem is directly con

tinuous with the root , and is the means by which leaves are

STRUCTURE OF THE SHOOT 65

spread out to the best advantage as regards light and ai r .

It is obvious,too

, that the stem is the means of communication between root and leaf . In order to bear the weight of

leaves and branches , and to withstand the strain Of heavywinds

,i t needs to be strong and to resist the attacks of

numerous enemies , i ts outer surface must be tough or

otherwise res istant . To prevent the escape of sap ,which

passes along the stem ,i t mus t be impervious . S tructures

thus exposed to many and varied cond itions,and having

to serve so many purposes,are likely to Show a wide range

in duration and modificat ion of form and structure .

Though the leaf and stem di ffer in many details from the

root,they are bui lt up of the same general tissues— an

epidermis on the outside enclosing a cortex , and,within

,

a ring of vascular bundles surrounding the central pi th .

In a leaf,however

,the blade of which is usually in the form

of a thin plate ,the veins spread out in the form of a flat

meshwork .

S tructure of the Box leaf.

— A s imple dissection wi ll Show

the relationship of these di fferent tissues of which the lea fis composed . Boi l a few Box leaves in a solut ion Of causticpotash for fifteen to twenty minutes , then wash gently inwater

,and place them on a glass slip . Dissect off carefully

first the lower skin , then the upper skin,and mount them

on separate slips (Fig . 29 ,I and There now remains the

skeleton,the meshes of which are covered by and filled in

with a soft green tissue . Wi th a camel—hai r brush carefully

remove this tissue, and SO prepare a clean skeleton (Fig .

Examine all these parts carefully with a pocket lens . How

do these skins di ffer Is one more readily removed than th e

other ? and if S o ,which What structures do you find on the.

under skin which are absent from the upper one Examine.

thesewith a microscope and als o the green t issue youhaveremoved from the meshes of the ve ins . Each of the dots

seen with a lens on the under skin cons ists of two sausage1 296. E


shaped cells j oined end to end , leaving a pore or mouthbetween them (Fig . 29,

I and 4 s) . These openings are

called stomata (S ing ,s toma , Gr . stoma the mouth) , and

thei r function is to communicate between the interior of

the leaf and the air outside . On the upper skin (F ig . 29,

however,these are almost or enti rely absent .

FIG . 2 9 . S TRUCTURE OF A B ox LE AR — 1, part of lower epidermis

2,part Of upper epidermis 3 ,

cross—section o f B ox leaf ; 4 , partOf 3 at th e point u , I, h igh ly magnified 5 , a cell o f th e mesophyll ;a ,

a ir -ch amber ; b, bast ; o,cu ticle Of epid ermis ; oh ,

ch loroplastg , guard cells ; 1 , lower surface t.e, lower epidermis n , nuc leus ;

P protoplasm ; P . t, palisade tissue ; s , stoma sp , spongy tissueu

, upper surface ; v,vein ; w,

wood .

A thin transverse section of the leaf should be examined

with a lens or microscope and the details shown in Fig . 29,

3 and 4 , identified . The green tissue between the two skinsis seen to be arranged in two distinct layers the upperone

, called the palisade tissue ,consists of perpendicular

elongated cells , closely packed together and attached aboveto th e upper skin (Fig . 29, 4pt ) . The cells below,

knownas the spongy tissue,

'

a_

re loosely arranged , leaving large


spaces between them filled with air (Fig. 29, 4 sp) . Thesecells contain the small rounded green bodies to which the

colour of the leaf is due . The bodies are known as chloro

phyll corpuscles or chloroplasts ,and the green colouring

matter as chlorophyll (Gr . ohloros=green , phyllon=a leaf) .It will be noticed that each stoma on the under surface

always Opens into one of these air- chambers (Fig . 29, a ) .

Between the two layers runs themeshwork of veins (Fig .

We can understand from such a section why the lower skinshould be more easily removed than the upper .

S tructure of the stem — Tu rning now to the tissues of a

stem like the Buttercup (Fig . Dead

nettle (Fig . or Bean ,we find these

s imilar to and continuous in structure with

those of the root/

and leaf ; and they are

also s imilar in function . A layer of cellsthe epidermis (F ig . 3 1 ,

e) — covers the oute r

surface,the exposed walls of which are

thickened with a protective layer the

cuticle. Stomata occur here and there as

in the epidermis of a leaf . Beneath thePM 30 .

epidermis is the cortex (co) , followed by a S KELE TON OF

ring of veins , or vascular bundles In BOX LEAF .

the centre is the pith (p) , which in older

plants breaks down,making the stem hollow . Broad rays

of tissue pass between the bundles from pith to cortex .

These are the medullary rays . These tissues— epidermis,

cortex , vascular bundles , rays , and pi th— occur general lyin plant stems

,but become greatly modified according

to the requi rements of the plant .The epidermis may develop a very thick cuticle in evergreens , and is usually waxy and more or less impervious .

In water-plants the cuticle is Often very thin or absent .

In some plants , hai rs are so abundant as to produce a woolly

covering . Not uncommonly some hai rs pour out a sticky

E 2


secretion , e . g . Campion and Catchfly while in otherplants they secrete a poisonous acid and the hai rs become

formidable stings , e . g . Nettle .

The cortex and mechani cal supporting tissues — Beneaththe epidermis is the cortex ,

and th e cells of the outer part,

especially in herbaceous stems , may be strongly thickened

SO as to form a firm supporting tube (Fig . 36 sol) . In the

Deadnettle ,the cortical cells of the angles of the stem are

strongly thickened at thei r corners (Fig . and these,

together wi th the wood of the large bundles , are effective in

protecting the stem against the s tresses of tension and compression in fact the whole s tem is built on the principleof a box girder . A tissue consisting of cells which retainthei r living contents , and whose walls are thickened at thecorners

,is cal led collenchyma (Gr . collen gelatinousmatter

,

chyma an infusion) . A ring of collenchyma occurs in

the outer cortex of the Sunflower stem (Fig . and i t

is frequently found in leaf- stalks . Bands of cells in thecortex of theBracken and B irthwort are uniformly thickened

and devoid of living contents . Those of the B irthwort

(Fig . 36) form a s trengthening ring immediately beneath

the epidermis (sol) , and a second one (so

?) as a strengthen

ing cylinder midway between the epidermis and the bast .

Such amechanical supporting tissue is cal led sclerenchyma

(Gr . skleros hard) .

The ring of wood in the Elder (Fig . 38 , w) forms a supporting mechanism on the principle of a hollow pillar

,while

in Older woody stems the arrangement is that of a solidpi llar . Woody tissues thus perform a double function—conduction of crude sap and mechanical support . Many

ingenious devices for mechanical support may be found in

the stems of plants,and several common species should be

compared in this respect .

S tructure and arrangement of vascular bundles — A com

parison of Figs . 3 1 to 34 and 36 to 39 ,wh ich are transverse


sections through the internodes of several dicotyledonous

s tems , shows that the vascular bundles are arranged in theform of a ring. Fig . 32 shows one of the vascular bundlesof the Buttercup ,

highly magnified . Note the three distinct groups of tissue of which it is composed . On theoutside is a group of delicate cells , the bas t or phloem (b)the larger elements— sieve tubes (3 )— are accompanied byvery smal l ones , called compan ion cells (o) both are fil ledwith organic material s . On the inner s ide of the bast is

a band of narrow,flattened cells— the cambium (ca) . In

that portion adj oining the pith is the wood or xylem (w) ,composed of wide, tubular, thick

-wal led vessels , among

which are narrower, thick-walled woody fibres . The veins ,as in the root

, are arranged in the form of a network and do

not continue the paral lel course which a section through

the internode might suggest . Numerous examples of thismay be obtained from waste heaps where shoots such as

old cabbage- stalks are undergoing decay .

With a li ttle trouble,the above details may be made out

by carefully dissecting the stem of a Deadnettle which has

previously been boiled in water for about twenty minutes .

Tougher s tems may be boiled in water to which a little

caustic potash has been added . This softens the cortical

t issues so that they may be brushed away from the veins ,as was done in preparing the skeleton of the Box leaf . I fa piece of stem including two or three pai rs of leaves be

selected , it will be seen that the veins , passing from the

leaves down the leaf-stalks , enter the stem,branch at the

nodes,and j oin on to neighbouring veins . This will be clear

from a study of Fig . 33 . By means of these veins directcommunicat ion is set up between roots , s tem,

and leaves .

Fig . 34 Shows the arrangement of these tissues in a t rans

verse section of the Deadnettle s tem . At the corners are

the large fused bundles from the leaves while at the

sides are the small bundles . In this stem the innermost


layer of the cortex stands out clearly as a layer of largercells— the endodermis (en) . Examine the mature stem of

the Bean and compare i t with that of the Deadnettle .

Al though these s tems are square , the general arrangement

of the tissues is th e same as that which is found in the

Bu ttercup .

S cattered bundles of M onocotyledons .

— The stems of

Monocotyledons differ in severalimportant respects from those j ust

described the vascular bundles ar escattered in the ground tissue (Fig .

and there is no cambium be

tween the wood and bast , so thatwhen once these bundles are formed ,no further increase in thi ckness is

possible in them. They are thereforecalled closed ’ bundles to di stin

guish them from the open ’ bundlesof Dicotyledons which possess a

cambium .

Woody stems . S eoondary growth .

The cambium of D icotyledons,

though a small and inconspicuous

tissue, is a very important one , in

asmuch as i ts cells are able to divideF I G ‘ 33 ' D IAGRAM

repeatedly and form new tissue.

S HOWING THE ARRANGEMENT OF V E INS IN That formed on its outer side beA DEADNETTLE S TEM comes part Of the bast , While that(after Farmerl formed on its inner S ide adds to

, and

increases the thi ckness of , the wood .

In a woody stem which lives for a number of years,cambium

is formed across each medullary ray , so as to form a cambium ring (Fig . 36, i .f. c) . Thi s later- formed cambium

,called

interfascicular cambium, p roduces small new bundlesbetween the original large ones , as shown in Fig . 37 . Growth

STRUCTURE OF THE SHOOT 7 1

continues , bundles are introduced ,an d ultimately a compact

ring of Wood is formed with thin medullary rays between

the bundles (Fig .

The formation of new tissue and especially of woodytissue goes on actively in the spring and summer ; less is

formed in the autumn and lit tle or none in the winter .On the return Of Spring, the process is repeated and as the

wood formed in spring consists of elements with much

larger cavities than those formed in the late summer and

autumn , the successive zones stand in strong contrast wi theach other, and may be clearly seen in a transverse section .

These annua l r ings (Fig . 39, a) are often irregular, and some~

times more than one ring may be formed in a season , buttheir number enables us to obtain a fairly accurate idea of

the age of a tree . By such increase some stems may grow

to a great age and size,and

,unl ike animals , they may add

to their body-substance year by year .These di fferent tissues may be determined by dissecting

a piece of Elder stem . Outs ide is the thi n dyi ng epidermiswith a layer of cork below next the green cortex , followed

by the slimy tissues of bast and cambium . The firm woodis easily discovered surrounding the central pi th . In some

stems , e . g . the Laburnum,the wood in the centre becomes

dense and dark- coloured and is known as heart -wood ’

while the newer,outer wood is soft and light in colour, and

is known as sap-wood The heart-wood usually serves

chiefly for the storage of water, the main ascending current

passing along the sap-wood

,whence i ts name .

Cork

Cork and lenticels .—During the early stages in the de

velopment of the woody tissue Of Dicotyledons , the outercells of the cortex and epidermis keep pace with it , buteventually they lose thei r power of increasing and tend togive way under the internal strain . Meanwhile, provision


is being made for a new protective covering . There arises

in the cortex another kind of cambium , known as the corkcambium , because i ts cells by repeated division form , notwood and bast , but cork . Fig. 38 shows this corkcambium

(c . c) arising just below the epidermis (e) in the stem of the

Elder, and i ts cells have divided in such a way as to formsomewhat regular rows of cells . These enlarge, lose thei r

l iving contents , and thei r walls become transformed intocork (ck) . The epidermis gives way under this extra strain ,producing the cracks which may be easily seen on the

surface of a twig . Thus the stem becomes covered by

a layer of cork , which is a dead impervious layer,well

adapted as a protective coat . As the stem thickens fromyear to year, the outer cork layers Split

, new layers are

formed beneath and the bark thickens , and in time takes

on the ruggedness characteristic of the species . Often an

i rregular group of cork cells is formed beneath a stoma , the

cells being so arranged as to permit ai r to enter or leave thestem . These structures

,which take the place of stomata,

are called lenticels (Fig . 42 ,l) and are formed on most

trees , their Shape being peculiar to the Species .

Other stems shoul d be examined and compared . In theLaburnum the corkcambium is formed in themiddl e of thecortex , while in the Black Currant it arises deeper still ,near the ring of vascular bundles (Fig . 40 cc .) AS the corkdevelops, the cortex to the outside of it dies and is eventuallythrown Off .

Callus and separation- layer .—The formation o f cork is

useful to plants in many ways , and especially as a means of

healing wounds . Examine the trees in a wood,look for

examples of pruning, and note the change taking placearound the cut surface of a branch . You will be able tofind all stages of cork- formation from a narrow ring justoutside the wood to others broader and broader, gradually

encroach ing and growing over the surface of the wound


is i t performed Do changes in any of the conditions af fect

the behaviour and growth of the Shoot Are the differences

we find in the form and structure of plants growing indifferent habitats correlated in any way wi th the differences

in thei r environment ? These are problems we must now

endeavour to solve .

CHAPTER VII

WORK OF THE SHOOT

WE have seen in the experiments with germinating seedsthat the main Shoot grows upwards towards the light , in

the direction opposite to that of th e mai n root , the stimuliproducing thi s resul t being gravity and centrifugal force.

We must now extend our knowledge by making one or two

further observations with older plants .P erception of and response to stimuli — Lay on its S ide

a plant of Geranium (P elargonium) or Bal sam in a horiz ontal position , as in Fig . 43 . Note at intervals the behaviour of both stem and leaves (a—e) the stem- tip turnsupwards and continues to grow vertically. Take anotheractively growing plant , lay i t on i ts side for an hour, then

place i t in a normal upright position and observe i ts modeOf growth . Does the tip show signs of turning while lyinghorizontal ly ? Does any subsequent bending take placeWe see that the stem . did not bend during the short time itlay in a horizontal posit ion , but bending does occur later,even after the plant is placed upright . This experiment

shows that a stimulus was received , though response wasnot immediate and i t is c lear that the stimulus persistsfor a time

,as bendi ng occurs even in the al tered position of

the plant .

WORK OF THE SHOOT 75

FIG . 43 . SHOOT OF BALSAM P LACED H oRI z ONTALLY ,S HOW ING

S UCCE S S IV E P HASE S OF CURV ATURE (a to e) (P feffer ) .

FIG . 44 . P LANT P LACED IN A H ORI Z ONTAL P OS I TION AND REVOLV EDS LOWLY BY MEANS OF A KLINOS TAT (Jost ) .


A few trials will enable you to determine the time requiredfor the stem to perceive the stimulus , and also that requiredfor curving . If a plant is fixed in a klinostat (Fig . and

caused to revolve in a horizontal posi tion ,the stem,

'

likethe root , does not curve,since i t receives the stimulusequally on all sides .F orce exerted by a growing

stem.~— Just as roots exert

much force in their down

ward growth in response tothe stimuli of gravity and

centrifugal force, so in the

reverse direction do shoots ,and thei r lifting power is

considerable . Obtain a

spring-bal ance, attach a

weight, and arrange i t as i nFig . 45 , over the stem of a

Bean seedl ing so that theweight is raised as the stemelongates . Fix the weightfirmly to the hook so thati t is not readily tilted

,and

FIG . 4 5 . EXPE RIMENT 1 0 DE

TE RM INE THE L IFTING P OWER OFdeterm me the ll ftlng power

A SHOOT . of the shoot . In the experiment illustrated , the shoot

in three days supported a weight of seven ounces .S timulus of light. Heliotropism.

—Consider next the

heliotropism Of the shoot .P lace a plant in a window so that light fal ls on i t on one

side only, and no te the behaviour of both stem and leaves

(Fig . In what direction has the stem turned Which

is the longer side of the stem , the one facing the light or theone which has grown in the shade ? Has the light hastened

FIG . 46 . SEEDLINGS TURNING TOWARDSTHE L I GHT .

FIG . 47 . BEAN SEEDLINGS .

- I, grown in th e ligh t ;

2, grown in th e dark .


or retarded growth These experiments Show that shoots

are sensitive to light , and that their growth is retardedby i t . Thus shoots turn to the light because they grow

more qu ickly on th e shaded than on the i lluminated side .

Such movements of plants due to the stimulus of light arecalled heliotropic movements . And since shoots turn

towards the light they are positively heliotropic . Notetha t the leaves also turn their blades towards the light .The leaves of some plants , however, grow erect and exposethei r tips and edges to the light , e .g . the Iris , Daffodil , andHyacinth ; this habit is common in plants growing in very

sunny situations .Rates of growth in light and in darkness — Take two pots

of seedling Beans , allow one to grow for two or three weeks

under ordinary conditions of light , and the other for a similar

time in th e dark (Fig . 47 , I add Compare them as to

colour,length of internodes

,and S ize of leaf . Measure them

day by day ,compare thei r behavi our and plot the results

in curves on squared paper as in Fig . 48 .

Etiolation . Conditions necessary f or the formati on ofchlorophy ll . —From these observations we learn that shoots

which develop in the dark are yellowish-white in colour,

greatly elongated and tender , and that the leaves are much

smaller than normal . These changes brought about by

growth in darkness are known as etio lati on (Fr . e’

tioler= to

blanch) . Shoots grown under ordinary conditions of light

develop the green pigm ent chlorophyll, and have tougher

tissues and larger leaves . Normally,chlorophyll is not

developed in plants from which light is excluded , but cases

of the contrary are not rare,e . g . P ine seedlings develop

chlorophyll in the dark ,and the embryo Of the Sycamore

is green while still enclosed within the thick and opaque

fruit- coat .Not only is light usually necessary for the formation of

chlorophyll,but we learned from water- cu lture experiments


that i ron is essential . The shoots grown in solutions fromwhich iron is excluded are a sickly yellow colour (Fig . 25 ,

o) .

Further, a supply of oxygen and a suitable temperature are

also requisite . If you examine the young shoots of plants asthey emerge from the soil in the cold early spring, you willfind they are often very pale

,and contain little chlorophyll .

2

Day

l

g

FIG . 48 . GROWTH CURV E OF BEAN SEEDLINGS .

a ,in th e ligh t ; b, in th e dark .

The conditions necessary for the formation of chlorophyll

are light , warmth ,and a supply of oxygen and iron .

We are now in a posi tion to realize some of the mostgeneral points of difference between roots and shoots .

These are,that roots grow downwards into the soil , avoid

light,are not green ,

and do not produce leaves , while shoots

grow upwards , bear thin flat leaves , and expose a large

green surface to air and sunlight . We will now endeavou r

to find out the importance of these peculiarities of a shoot .


and gi ve off oxygen ,whereas non—green ,

living parts or

green leaves kept in darkness are unable to bring aboutthese changes . This absorption of carbon diox ide by green

plants under the influence of sunlight is called photosynthes i s (Gr . phos , photos light , synthesi s a puttingtogether) , or carbon-assim i lation .

That plants do give off oxygen under such conditionsas above described may be shown by an experimentarranged as in Fig . 5 0 . Take a jar or beaker filled withtap

—water and saturate the water with carbon dioxide .

P lace in the water a branch or two of Canadian W aterweed

(Elodea canadensi s) , with the cut ends uppermost , and overthese a funnel with a shortened stem . Completely filla test tube wi th water and invert i t over the stem of the

funnel then expose to sunlight . Set up a S imilar experiment

,but instead of charging the water wi th carbon

dioxide,drive off all the dissolved air by first boiling the

water , and then allowing it to cool, or

— simpler still— add

lime-water to i t so as to remove all the free carbon dioxide .

P lace the bottles side by s ide and compare .

In the second case it will be found that few or no bubblesare given off , but in the former, bubbles are given off freelyand displace the water in the inverted test tube . Whensufficient gas has accumulated , test it with alkaline pyro

gallic acid and note how suddenly the brown colou r is

produced,or insert a glowing match which at once bursts

into flame these are proofs that the gas given Off is oxygen .

We thu s see that such a plant when growing in watercontaining carbon dioxide

,and exposed to sunlight , gives

Off oxygen .

F ormati on of starch in green leaves . S tarch prints — We

have seen in a former chapter that starch is commonly

present in the tissues of roots and stems . We have now

to consider how this starch makes i ts appearance and underwhat condi tions i t i s formed . For this purpose ,

plan ts of

WORK OF THE SHOOT 8 1

the cultivated Geranium serve very well . Keep a plant

in the dark for a day , then partially cover two or threeof the leaves while still on the plant with black paper ,tin—foil

,cardboard

,or pieces of cork

,as shown in Fig . 5 1 ,

I,

in such a way that light is excluded from one part of theleaf while the other may be illuminated . P lace the plantso prepared in sunlight for several hours or , if more con

venient , on two or three successive days . At the end

F IG . 5 1 . EXP ERIMENT To SHOW THAT S TARCH I S FORMED IN

GREEN LEAV ES WHEN EXPOSED TO L IGHT .— 1

,leaf covered with

Opaque paper, from wh ich a cross has been cu t ; below i s a corkpinned to th e leaf to exclud e th e light ; 2

,th e same leaf wh en

tested later wi th iod ine solution ; th e Sh ad ed areas contain starch .

of a period of several hours’

illum ination make the

following test . Have ready some boiling water ; remove

the covered leaves , noting that they are still green ,and

plunge them at once into the water to kill them . Next

place the leaves in alcohol , by wh ich means the greencolouring matter is gradually extracted . (This may be

hastened by boiling in alcohol , but i t must be done very

carefully to prevent ign it ion of the alcohol vapour . ) The

resulting colourless leaves Should be washed in water, then

laid out in a shallow dish and covered w ith iod ine solution .

1 296 F


Watch the effect of the iodine,and note that the parts

which have been kept in the dark remain colourless or

are merely stained yellowish brown , while those whichwere exposed to light take on a blue-black colour (Fig . 5 1 ,

indicating the presence of starch,which appears only

in those parts to which light had access .

1

Condi ti ons necessary for the formation of starch .

— A

similar test should be made with leaves of a variegatedGeranium, one with white patches on its leaves beingselected . The leaves need not be covered

,but after exposing

the plant to sunlight as in the previous experiment , testfor starch by the same methods . It wi ll be seen thatstarch is formed only in the parts that are green .

With a Geranium plant that has been kept for a day

in the dark arrange an experiment as shown in Fig 52 .

P lace a l i ttle caustic potash solution in the bottom of

a bottle , til t i t as in the figure and turn into it a leaf of

the plant , taking care that the leaf does not touch theliquid . Close the bottle with a split cork perforated to

admi t the pet iole without injuring it , carefully seal thecork with vaseline, and then expose the whole to sunlight

as before .

Now consider the following points : What effect will

the caustic potash have on the air in the bottle ? What

changes take place in the composi tion of the air by theaction of a green leaf Test the leaf as above and deter

mine whether starch has been formed under the cond i tions

of this experiment ? We have seen that plants absorb

oxygen from the air and give off carbon dioxide ; thisis the process known as respiration or breathing ; alsothat a green leaf exposed to air containing carbon dioxide

1 I f it i s necessary to carry ou t th ese experiments during verydu ll weath er, satisfactory resu lts can be Obtained by exposing th ep lants to artific ial ligh t, care being taken not to in jure th e p lantby h eat .


is able,under the influence of sunlight , to absorb carbon

dioxide and give off oxygen , and further , that the light

rays absorbed are converted into forms of energy capable

FIG . 52 . EXP ERIMENT To SHOW THAT A LE AF OF P ELARGONIUMEXP OSED To L I GHT IN AI R DEVO ID OF CARBON D IOXIDE DOES NOT

FORM S TARCH .

of bringing about chemical changes result ing in the forma

tion of starch . But starch is found only in those partso f leaves which contain the green pigment chlorophyll ,and the experiment just performed proves to us another

F 2


important fact,namely , that a green leaf , working under

normal condi tions,but in air devoid of carbon dioxide ,

is unable to form starch . In addition to the above condit ions i t is found that the work of a leaf can only proceed

a t a suitable temperature and when the plant is ableto Obtain a sufficient supply of water . Thus moisture

,

warmth ,sunlight , carbon dioxide, and chlorophyll are

all necessary for the formation of starch in a leaf .If we think over the previous experiments we meet

with an apparent contradiction . We have just learnt thatstarch is formed in green leaves only under th e influence

of sunlight , and not in parts that do not contain chlorophyll , yet we found an abundance of starch in the

cotyledons Of the Bean and in the endosperm of theWheat

and other grains and it also occurs , as we shall see, in thenon - green parts of stems and roots . It is Obvious , therefore,that starch arises In more ways than one within the tissuesof a plant .Now the starch grains formed in green leaves are

formed entirely from inorganic substances the exactmethod is not known , but a possible explanation is thefollowing

C0,

H,o

(carbon d iox ide) (water)

6 HCOH

( formaldehyde)

” (CGHWOB)(sugar)

In words , the carbon dioxide and water within the living

chlorophyll- containing cells of the leaf , and under thecondi tions already enumerated

,may be spli t up and thei r

constituent atoms rearranged to form a compound called

formaldehyde and also the element oxygen . This will

HCOH

(formaldehyde )

CeHmOc

(sugar)

(starch )


account for the carbon dioxide taken in and the oxygen

given out during photosynthesis . Sixmole cules of formalde

hyde are now supposed to combine to form sugar . By

further action the sugar is deprived of a molecule of waterand is converted into starch . Another possible explanation

is that during sunlight Chlorophyll is continually breaking

down and re- forming,and formaldehyde may be one of the

products formed as a result Of the decomposition of the

chlorophyll . This building up of starch grains is intimately

associated with the chlorophyll corpuscles , but when formed ,

they become detached and lie in the cavity of the cell .

These grains , however , are solid , and ,as we have learnt

from our experiments in osmosis , are qu i te incapable of

being transferred from cell to cell in this form . Obviously ,if the grains are not removed , the cell will soon reach i tslimi t of activity in this direction .

S tarch digesti on— The following experiments will help us

to understand how the transference of food-materials is

brought about . P lace a little potato starch in a beaker , add

water,and note that the starch grains are not dissolved . On

boiling the liqu id for a fewminutes , a muci lage is produced ,

but the starch does not completely disso lve . D ilute this

with cold water . P lace a little of the cooled l iquid in a test

tube , add saliva from the mouth,mix thoroughly, and keep

it at the temperature of the body for fifteen or twenty

minutes . This may be conveniently done by enclosing thetube firmly in the left hand whi le the following experimentsare carried out . To another portion of the weak mucilage

add a l i ttle ' diastase or malt - extract (which containsdiastase) , and allow i t to stand at the temperature of the

room for twenty minutes or more . In the meantime take

another test tube and place in it a l ittle grapesugar , add

water to it , and note how readily the sugar dissolves . Take

a small portion of this , test i t with iodine solution ,and

note that no Vi olet colorat ion results . To the remaining


portion add Fehling’

s solut ion ‘and boil . Note the deep

orange colour produced . This react ion is characteristic of

grape-sugar . Test by the same means (I ) the juice of theGrape and (2 ) a few small pieces Of Onion and compare the

results . Grape- sugar occurs abundantly in each case ; it isof common occurrence in plant tissues , and is a valuableand easily transported food . Now examine the starchmucilage which has been acted upon by the saliva . Notethat the mucilage has dissolved . Test a small portion with

iodine solution . Is starch present As no violet colorationresults , wemay conclude that the starch has been convertedinto some other substance . To the remainder add Fehling

’

s

solution and boi l . What is the new compound formed ?

From this experiment we learn that saliva contains a

substance which has the property of converting starch intosugar . Such a body is called a ferment or enzyme , and i t

is by means of such ferments that we are able to digestthe starch present in our food . The starch- digest ing fermentin saliva is called ptyalin . Apply these tests to the solutionacted upon by diastase and compare the results . In thiscase also the starch has disappeared . Diastase is a ferment

commonly present in plant cells , and it is by means of

such ferments that the insoluble starch grains are corrodedand disorganized , and finally converted into sugar .We have seen above that sugar is formed in green leavesduring sunlight . Part of this is converted into starchgrains within the cells of the leaf the rest is drained awayto the stem or other parts . In these organs it may either

(I ) be converted into starch and stored , or (2 ) serve for thenutrition of tissues that are growing . At n ight , when the

Feh ling’

s solution may be prepared and kept in two stock solu tionsas fo llows : ( I ) d issolve 35 grammes Of cupric su lph ate in 2 0 0 c c .

o f water ; ( 2 ) d issolve 7 0 grammes Of roch elle salt in 2 0 0 c c . Of

a 1 0 per cent . solu tion of cau stic soda . When requ ired ,make a

solu tion Of equal volumes Of I , 2 , and water .


Chl orophyll , the green colouring matter of plants , is

a very complex nitrogenous substance . AS we have seen

(p . 8 1 ) i t may be extrac ted by means of alcohol , and ifsections of leaves so decolorized are examined u nderthe microscope the corpuscles wi ll still be found in the

cells (Fig . 29, 5 ch) . In the living plant the pigment is

probably dissolved in some Oil,and this solution is enclosed

in the meshwork of th e corpuscles . Each chlorophyll

corpuscle or chloroplast , therefore, consists Of (a) a protoplasmic body or plastid and (b) a pigment , chlorophyll .Light rays absorbed by chlorophy ll .— An alcoholic solution

of chlorophyll is fluorescent if it is held up to the light

and examined it is green ,but if examined against a dark

background it is blood- red . Examine a beam of l ight

by means of a spectroscope and note the band of coloursred , orange ,

yellow , green , blue , indigo ,and violet . Th is

band is called the spectrum of whi te light . P lace an

alcoholic solution of chl orophyll in the path of a beam

of light before i t reaches the sli t of the spectroscopenote the Spectrum which results , and compare i t wi ththat of white light . Observe the dark bands producedand note carefully thei r position in the spectrum . Sevenvertical bands are produced ,

but some of them are di fficul tto see . The darkest is at the red end of the spectrum ;

three fainter , but broader , bands occur at the blue end

the remaining three bands are much paler and occur i nthe yellow and green . We thus see that the rays of lightfall ing on a green leaf do not al l pass through i t . Chlorophyll has the power of absorbing most of the red rays

,

many of the blue and violet ones,and

,to a much less extent ,

some of the yellow and green . It is the energy thusabsorbed from the sun

’

s rays that enables the chloroplaststo carry on the constructive work of photosynthesis . We

are now able to understand why starch is not formed in thewhi te parts of leaves or in green leaves kept in darkness .


Currents in the stem.

-Let us now perform a few experi

ments which will enable us to determine the channels

along which travel thematerials used by the shoot .

P lace in a bottle red ink or a solution of eosin ,and Obtain

shoots of Rhododendron ,Ivy

,or similar evergreen . P lace

the freshly- cut ends of th e shoots in the coloured solution .

From one of these , and above the level of the solution ,

cut a broad ring of tissue into the wood . P lace a similarshoot in another bottle,

but instead of eosin ,use water to

which a li ttle finely- powdered carmine has been added .

The particles are exceedingly minute and of such a nature

that they remain in suspension a long time and producea coloured liquid . Leave these for a day or two and then

compare them . Are they equally fresh ? Is there any

difference in colour in the shoots Cut short pieces fromthe lower end of each and compare the cut surfaces . How

do they differ Cut off a piece two inches long and split

i t longi tudinally down the middle . IS the stem uniformly

coloured Are the Shoots coloured similarly ? Scrape off

some of the bark and determine which tissue is coloured .

Trace this coloured tissue upwards and determine whetheri t extends into the leaves . Cut the leafstalk and leavesacross and note whether they are coloured ; and ,

if so,how ?

What do we learn from these experiments ? We findthat the shoots in eosin have taken up th e coloured solu

tion , and it has ascended only through the woody portions

of the stem and leaves , and not through the bast , cambium ,

cortex , or epidermis , for in the shoot from which thesetissues have been removed the eosin has ascended , not

withstanding thei r removal . The shoot in carmine ,

however, remains uncoloured . Why ? Here the fine

part icles of carmine are in suspension ,not in solution ,

and al though a coloured solu tion like eosin may be

absorbed , the particles , even so fine as those of the

carmine, are unable to pass through the woody tissues .


Water, however, is absorbed and serves to keep the shootfresh , while that in eosin becomes discoloured and dies .Judging from these experiments we may conclude thatthe wood of such a shoot is the path along which waterascends through the stem to the leaves . But what of theo ther tissues of the bundl e, for example the bast

If we examine the plants in a garden or park, especiallyshrubs or trees which have been tied for some time to

a support , it will be interesting to notethe mode of growth in the neighbourhoodof the l igature . Fig . 54 is a sketch Of

a rose stern which has been t ied in thisway and allowed to grow for some time

wi thout further attention . Careful examination of such a Shoot shows that , asthe stern has grown in thickness , thel igature has gripped it with increas ingpressure

,and the delicate tissues of the

inner cortex and bast have been SO com

pressed that substances could not passalong them , but the rigid walls of the

F I G 54 woody tissues have wi thstood the pressure,L I

SFTI

H’

EE

RoiEEM

and sap can still ascend as usual . The

chief changes no ted , however, affect theportion of the stem above the l igature .

Here nutrient materials have accumulated , obviouslycarried from a higher level , and have become stored inan abnormal t issue which forms a swelling .

Flu ids are able to travel not only upwards through the

wood and downwards through the bast , but there are manycross - currents as well , especially through the thin plates

of t issue ,the medullary rays , pass ing from pi th to cortex .

In some stems these tissues become loaded wi th foodmaterial s carried to them from leaves and other parts .

This is seen very clearly in the Clematis . Obtain a piece


contents of the vessel . Weigh again ,and note the difference .

To what is this increase due and whence has the watercome This giving Off of water by living shoots is cal led

transpiration . A vessel with the dry calcium chlorideweighing together 1 6 grammes has been found by experi

ment to have gained I gramme in weight in twenty- fourhours i . e . the leaves have given off

during twenty- four hours 1 gramme

or 1 cubic centimetre of water .

If this water has come from the

leaves , has i t come equally fromthe two surfaces , and are leavess imilar in thi s respect ? To determine these points

,prepare a few

sheets of cobalt paper by dippingpieces of fil ter-paper in cobaltchloride solution and allowing themto dry . Test a small piece of this

paper and note the Changes in

colour that occur (I ) when the

paper is warm , and (2) when ex

F IG . 5 5 . EXPE RIMENT posed to ordinary air or whenTo DETERMW E THE breathed upon . Obtain a dry duster ,AMOUNT OF WATER

fold i t several times so as to makeGIVEN OFF BY A P LANT .

vessel containing a pad , and lay on i t a few leaves ,calcium ch loride . some with th e lower , others with

the upper surface to the duster .

P lace over these a sheet of dry (blue) cobalt paper, and

cover immediately wi th a sheet of thick glass to exclude

the air from the cobalt paper . Try this with several kinds

of leaves,including some evergreens , and note the changes .

Which surface gives off the more water ? Are there any

differences in this respect in the different leaves you have

examined From what we have seen in the structure of

a Box leaf , is i t likely that the differences noted can be

WORK OF THE SHOOT 3

accounted for by differences in the distribution of

stomata ?Take two evergreen leaves , as nearly alike as you can

find, and coat the upper surface of one leaf and the under

surface of the o ther with vaseline . Carefu lly weigh eachthen expose both to air for half an hour or more, and weigh

again . What difference do you find ? HOW does th is

result compare with your previous experiments ? As

previously seen , a cut shoot placed in water absorbs a con

siderable amount of liquid , and we now see that water ,in the form of vapour , is given off from the leaves through

the stomata.

Let us now try to determine the rate at which this

water travels , and the amount absorbed in a gi ven time .

To do this , arrange an experiment as shown in Fig . 56 .

Take a wi de-mouthed bottle provided with a tight- fittingrubber stopper with three holes . Through one is passed

the tube of a funnel provided with a tap . Through thesecond is passed a bent , thick-walled capillary tube ,

passing only to the lower level of the stopper . Behind

the tube is a scalemarked in inches or centimetres . Through

the third hole is passed a shoot which has previously

s tood in water (Rhododendron or Laurel wi ll answer very

well) . Fill the bottle completely with water and press

the stopper, together with shoot and tubes , firmly into thebottle . If the tap of the funnel is open ,

water rises in thetubes . Now close the tap and fill up the reservoi r . By

opening the tap , water flows along the bent tube and drops

from the open end . Now close i t,and the water stops

immediately . As the shoot absorbs,water is drawn back

along the tube and readings may now be made . Careshoul d be taken that the temperature is fairly constant .

Obtain the capaci ty of the tube and determine the amoun tof water absorbed in a given time .

By turning the tap , the tube may be refilled and the


experiment repeated or varied in several ways ; e . g . bycoating some Of the leaves wi th vaseline (I ) on thei r

FIG . 56 . P OTOMETER , To MEASURE THE RATE OF

TRANS P IRATION IN A SHOOT (Farmer) .

upper and (2 ) on thei r under surface ; (3) by removing

some of the leaves ; (4) by exposing the apparatus to

sunlight or (5 ) to diffused light ; or (6) to dry air or (7)to moist air .


(and many fruits) provide S imilar examples , and in eachcase we find that the waxy coating very effectually preventsthe surface from becoming wetted . Further modi ficat ionswill be noted in connexion with the habitats of plants .

$

In the familiar process of wilting we have another goodillustration of transpi ration . Take two shoots and placethe freshly-cut end of one in water, but al low the other

to lie on the table . Compare them in an hour . The one

in water is fresh and rigid , while that on the table hasbecome limp , i . e . the shoot cut off from its water—supply

FIG . 5 7 . EXP E RIMENT To ILLUS TRATE TURGIDITY .

— I, piece o f

Daffod il sta lk ; 2, cut into two strips ; 3 ,

cut into four strips ;4 , th e same in water .

has wilted . Similarly ,if a plant rooted in the soil be

insufficiently watered it wilts , i . e . i ts Shoots and leaves

become l imp and droop ; but such a plant soon regains

i ts freshness and turgidi ty on being watered .

Turgidi ty .

— A simple experiment will help us to under

stand this . Take a piece of the flower- stalk of the Dandelion

or Daffodil,abou t three inches long ,

and cut i t down the

middle, as in F ig . 57 ,2 . Does any Change in shape take place

Which is now the longer side ? the inner or the outer ?

The inner side being the convex and therefore the longerside

,in what condi tion were the tissues of this surface

before th e stalk was cut Clearly they were compressed ,

FIG . 58 . EXCRE TION OF WATER BY WHEATSEEDLINGS .

FIG . 59 ._

LEAF—ROSE TTE OF A SAXIFRAGE .

—Th e margins o f th e leavesare encru sted with lime from Ch alk gland s at th e ends o f th e teeth .


when the water evaporates this occurs in Wheat seedlings ,and especially in some Saxifrages , where the salts formchalky incrustat ions on the ends of the teeth (see Fig .

Water is usually gi ven off, however , in the form of vapour,

especially during the day ,when the stomata are open ;

loss of water may be so great in warm sunny weather

that the plants droop . At n ight the stomata close,but

absorption of water by the root goes on ; the plantsbecome turgid , and as the amount absorbed exceeds theamount of water-vapour transpired ,

water in a liquidstate i s forced out of the leaves . Some leaves

, e . g . the

Garden Nasturtium,have special stomata whi ch are

permanently open for this purpose and are called water

stomata .

Obtain an act ively growing plant of Sunflower , Fuchsia ,

or Dahl ia ,cut off the shoot abou t three inches above the

soi l,dry the cut end and examine the surface with a pocket

lens . Soon water exudes from the cut surface . Arrangean experiment as shown in F ig . 60 . By means of rubber

tubing (c) , attach to the stump (s) a bent tube (g) . Water

(W) now collects in this tube ,and if mercury (Q) is

placed in the bend of the tube , the column wi ll be forced

upwards . By this means the pressure of exudat ion may

be measured . The pressure which exists in the t issues of

the root and aids the upward flow of sap in the stem is

called root-pressure .

The amount Of sap which ascends in the stems of plantsin spring i s Often very great . If

,for example , the stem

of the Vine is cut as the leaves are unfolding , so greati s the flow of sap ,

that it can only with d ifficulty be

stopped . This exudat ion of sap i s known to gardeners

as bleedingF orce of transp irati on — It is obviou s that considerable

force must be exerted in drawing water up a stem to the

leaves to replace that gi ven off as water-vapour through


the stomata . Some idea of this force may be obtained

from the following experiment (Fig . Take a long ,thick-walled glass tube fitted at ' one end with a rubber

FIG . 60 . EXP E R IMENT FIG . 6 1 . EXPE RIMENT 1 0TO S HOW THE P RE S SURE DEMONS TRATE THE SUCTIONOF EXUDAT-ION (Jost ) . ACTION OF TRANS P IRATION

(Jo st) .

stopper . Through a hole in the centre push the end of a

Laurel Shoot,selecting one thick enough to fit t ightly .

Then fill the tube completely with water and ,placing the

thumb over the open end to prevent escape of water , put

this end into a trough of mercury . Remove the thumb and

G 2

1 0 0 THE VEGETATIVE ORGANS

secure the tube with the shoot to a retort- stand or othersu itable support . Fix a scale to the tube and take readings

at intervals . When the mercury has reached its maximumheight , ascertain the weight of the column of mercuryraised by the force of transpirat ion .

After a t ime, air will collect in the upper part Of the tube .

Where can this air have come from ? Is it possible that

the tension of the l iqu ids has resulted in air being drawnthrough the stem,

and that this has accumu lated on the

top of the column ? Or did the water contain air whichmay have risen to the surface ? The value of the latter

suggestion may be tested by using water which has been

previ ously boiled and allowed to cool . If air then accumulates it must have come from some other source . The

former suggestion may then be considered . DO air- channels

exist in shoots and ,if so , is it possible to draw air through

them ? The following experiment will help us to answer

this question .

Suction of air through a shoot — Fix a suction-pumpfirmly to the water-tap and connect it to a bottle by means

of thick-walled rubber tubing . Fill the bottle with waterand insert a rubber stopper , th rough

'

the -hole of which

is passed the stem of a Lau rel or the stalk of a S Ingle leaf ,as Shown in Fig . 62 . Turn the tap gently,thens teadily

increase the flow . Note what happens at the end of the

shoot . Where is the air coming from ? Is a stream of

air passing through the ShootThis experiment may be reversed . P lace the leaves

in the water and the cut end of the shoot in the air ;

observe the air-bubbles coming out from the numeroust iny points on the under su rfaces of th e leaves and more

vigorously at any broken or injured places . Suddenly turn

off the water and note the change of colour in the lowersu rface of the leaf . Why is this Turn on the water again

and the leaf regains its colour . Repeat the experiment


of the sun’s rays in bringi ng about and carrying on manyimportant changes in the substances entering the cells ,also of rearranging thei r component atoms and buildingup new compounds from them . During these chemical

changes much heat is evolved , as we have already seen inthe experiment with germinating peas but the leafy Shootsof plants are always cool , and commonly cooler than thesurroundi ng air . How is this ? Wi th all the chemical

changes going on in plant- t issues , why does the temperatureof the plant not rise much above that of the air , as i t doesin our own bodies Some heat may be lost by radiation ,but for a fuller answer we must go back to our experimentson transpirat ion and try to realize the enormous amount

of heat required to convert the water of the cell-sapinto vapour, and the large amount of vapour given Off

by an average leafy Shoot . It is estimated that over

90 per cent . of the heat absorbed by a plant is dissipatedin th is way . No wonder

,then , that the foliage of a plant

feels cool to the touch .

But our experiments with water- cultures suggest another

interesting point in this connexion . Is the soil-water

(or i ts artificial representative ,a water- culture solution)

a dense ,or a weak , food-solution Is i t necessary for the

solution to be a weak one ? and ,i f so, why ? If a plant needs

to take up an enormous amount of water in order to obtain

a sufficiency of solid food, what is the consequence The

necessities of osmosis , of conduction and transmission ,require a weak food—solut ion . This involves the absorption

of an excess of water above that needed for the bu ilding

up of tissue-materials . Hence we see the value o f a th in ,

flat leaf whose exposed surface is very large compared

w ith the amount of i ts tissue . Again,the spongy tissue

of a leaf, wi th all i ts cells hung out, as i t were,

in dryingchambers

,has an interesting meaning. These chambers ,

communicating by way of the s tomata with the air outside ,

WORK OF THE SHOOT 1 9 3

render the whole an admi rable arrangement for getting rid

of the excess of water . It seems from this that a large

leaf-surface might co incide wi th great absorption ,involving

a large food- supply and consequent rapid growth . At anyrate this is worth keeping in mind

,and i t might be considered

with reference to the very different conditions under which

plants grow . What differences,for example

,do you find in

the rate of growth and the forms of plants growing in a

di tch,a hedge

,on amoor

,a rock

,a sandy shore ? Meanwhi le

,

we see how important i t is that the functions of the s tomata

shoul d not be interfered with,and some of the mos t

interesting modifications of leaves are those which concern

the protection of the stomata and the economy of a plant’s

water-supply .

CHAPTER IX

BUDS AND BRANCHES

AT the growing end of a branch the leaves are very small

and immature , and ari se close together on the shoot- axis,

as shown in Fig . 67 . Such an undeveloped shoot is called

a bud . In winter the leaves of the buds are often so tightlypacked , and the parts are so small

,that they are difficu lt

to dissect . The essential features,however

,may easily be

made out from an examination of a Brussels Sprout

(Fig . Each sprout arises in the axil of a leaf, l ikethe bud of any typical plant . Remove the tightly-packed

leaves one by one, noticing that they are folded , wrinkled ,and arranged spirally on the axis . In the axil of each leafa small bud will be found . How many leaves are there

How many axillary buds can you find When you haveremoved all you can , cut the remainder of the bud (the


heart longitudinally into halves and make out bymeans of a pocket lens the end of the axis or growing-point ,covered over by many tender , undeveloped , or rudimentaryleaves . Such a bud is Clearly a condensed , immature

branch- system,consisting of a central axis , which bears

FIG . 63 . BRUS SELS S P ROUT IN V E RTICAL SECTION .

leaves , in the axils of which buds are formed,each Of these

being the beginning of a new lateral branch .

If we now examine a Cabbage and Cos Lettuce we see that

in such cases the axis elongates SO li ttle that , when theplants are full grown and ready for market

,they still bear

all the characteristics of huge buds . They are not protectedon the outside

,however

,by tough scales , and are hence

called naked buds . It will be interesting to compare with


in the Ribwort . Note the differences in the length of theleaf- stalk and the s ize of the blade from the lower and outerto the upper and inner part of the rosette

, and observe howthis prevents much overshadowing in spite of the crowding .

Leaves springing from the stem near the ground in this

manner are called radical leaves to distinguish them fromleaves ri sing

,like those of a S tock , on a taller stem above

ground and known as cauline leaves . The habi t of formingrosettes is very common in plants growing on mountains ,and on rocks where the soil is liable to dry up at certain

seasons . But rosette- formers are not uncommon in otherhabitats , especially in grassy swards . AS the buds whi charise in the leaf—axils of such plants also tend to form rosettesclose to the parent , a large cushion is in time produced .

Short lateral shoots of this kind are cal led offsets , and theyserve as an important means of vegetative reproduction

(Figs . 64 and

If opportuni ty offers,i t will be interesting to study the

vari ous rosettes of the plants growing on a rockery You

will find many forms,some compact , o thers lax . There

wi ll be varying lengths of offsets , and varying forms and

sizes of cushions . Fleshy leaves in all grades may be found ,some

,like those of the Houseleek , very thi ck indeed and

able to store much water for use in times of drought .

Observations on opening buds .

— If you p lace winter shoots

of trees in water for a few weeks you will be able to watch

the opening Of the buds , and i t is easy to study the more

important details of their structure. In such opening buds

Observe : (I ) the number and arrangement of bud- scales ;

(2 ) their origin from leaves , leaf-bases , or stipules ; (3) thetransi tion from bud - scales to foliageleaves (4) the

arrangement and manner of folding of the foliageleaves

(5 ) whether the leafstalk or blade is first developed

(6) the behaviour of the leaves as they expand ; (7 ) the

differences between leaf-buds and those containing flowers .

BUDS AND BRANCHES 1 0 7

Try to realize the great amount of work which is going on

as the buds open , and to determine where the materialcomes from and how it is utilized . If opening buds are usedinstead of germinating peas in the experimen t we have

performed previously (p . you will find that they

absorb a large amount of oxygen and give off much carbondioxide. It has been found that during this period of

active respiration many of our common trees lose from

2 0 to 45 per cent . of their total dry weight . This helps usto appreciate the fact that respiration is a wasting or

breaking-down process .Li lac — Quite different from the rosette type are the budsof the Lilac . If we watch them expanding in the spri ng

we shall see that the leaves are not folded and wrinkled ,

but lie flat and edge to edge . As the shoot grows and the

axis elongates,the leaves are seen to be in crossed pairs

which have separated by distinct internodes (see Fig .

The arrangement Of the leaves on the stem , and the relative

positions of leaves of different sizes , stand in strong contrastwith what we find in a typical rosette. Compare the leaves

from below upwards , and notice the transition from small

scal es below,followed by larger ones

,to the mature leaves

with longer, grooved stalks and large, heart- shaped (cordate)

blades . The bud - scales of the Lilac are thus reduced leaves ,of which the lower

,smaller ones fall off as the season

advan ces, not when the bud opens, as in many trees .

P rivet. — Now compare the Lilac shoot with a Shoot of

the Pr ivet (Fig . Note the smal l,brown scales below

their arrangement and the varying s izes and shapes, notonly of the scale- leaves , but of the green foliageleaves ;also the varying positions of the blades in shoots taken

from the side and from the top of the hedge . How are

these differences related to the direction in which l ightfalls on the shoot What part of the leaf is concerned inbringing the blade into such a position The movement


occurs at the leaf-base . This is of common occurrence in

plants ; and the Yew,Ivy

,and V i rgi nia Creeper provide

further interest ing exa mples . By means of a pocket lenscarefully examine the mode of attachment of the leaf to

the stem . The three parts of a typical leaf are easilydetermined : (1 ) the swollen base,

each

S ide r unn ing as a ridge down the stem ;

(2 ) the short stal k marked off from the

base by a dark transverse line, and (3)the ovate

,entire, acute blade .

Bend the leaf back and press thebent stalk agai nst the stem until i tsnaps . Where does the break occu r ?Repeat this and notice that the dark

line is a line of separation (Fig . 65 , s ) .Examine Older Shoots for leaf - scars , andnoti ce that when the leaves fal l it is the

blade an d stalk that are thrown off, and

that the base remains on the ax is as a

more or less promi nent scar . Compareother Shrubs and trees in this respect ,e . g . the Common Ash .

Horse-Chestnut.— If a twig of HorseChestnu t (Fig . 66) be examined we may

learn much of its hi story . At the end i sF1 0 ° 6 5 ° SHOOT a large terminal bud , and below th is are

OF P RIVE T . l .s ,

leaB ear ; 8 , separa_

two large leaf- scars each show mg seven

dots , Wt h are the broken ends of veins ,whi le above each scar is a small bud .

Lower down ,at intervals , are other crossed pairs of scar s and

buds , the lowest of the series being frequently smaller tha nthe rest , and below these again we find a number of smallscars crowded together . Even these are in crossed pairs,the scars being the scale- scars of last year

’s terminal bud ,

and in their axils are t iny buds which , in ordinary circum


upwards, their tips, for a time,being fastened together by

hairs, which soon fall Off as the leaf grows . One by one

the leavesmove outwards the leaflets expand and , growingmore on the upper than the under side

,bend backwards

unti l only the upper surfaces can be seen . Growth on theunder side now qu ickens

,and the reverse process occurs,

the leaflets being raised unti l they reach a horizontalposit ion .

When all have unfo lded , examine the Shoot from aboveand notice that they form a closely-fitting pattern , ormosaic . The leaf-blades are mostly at the same level ,though they arise at different heights on the stem. The

lowest leaves have the longest stalks and the largest blades

the highest leaves have the Shortest stalks and the smal lestblades those between being intermediate in these respects .

Meanwhile the scales fall off,the lowest first , leaving

narrow,light -brown scars which darken with age . We can

thus watch,day by day ,

the formation of ring or scalescars which indicate the begi nning of a year

’

s Shoot . The

uppermost scales have larger bases,are thinner, and turn

green , and often remain for some time on the branch afterthe rest have fallen off . Then they frequently developlittle blades (Fig . 69, s ) , which are di fferent from the lower

ones and are in some respects intermediate between them

and the foliageleaves . The fact that they may bear blades

suggests that the true scales are really leaf-bases , the blades

being u sually suppressed . When the intermediate scales

do fall off they leave larger and lighter scars than the

others . The broken ends of their veins are well seen,and

i t i s easy to detect their scars , even on old twigs .Usually seven leaflets are formed

,which arise from the

top of the leafstalk , but often there are only five,and

occasionally six occu r,in which case the leaflets are not

arranged three on each side,but there is a median one with

two on one side and three on the other . When the veins

FIG . 6 7 . VE RTICAL SECTION OF BUD OF P INE .

Note that th e growing point i s protected by overlappingleaves l , leaves wh ich bear bu d s in th eir axils .

2

7 8

FIG . 68 . OP ENING BUDS OF HORS E -CHES TNUT .— Th e shoot 5 )


FIG . 70 . S YCAMORE BUDS .— I

,winter shoot Of Sycamore with

a large terminal flow er—bud 2— 1 0 , th e parts of th e bud d issectedout 2— 7 , one o f each pair of bud - scales 8—9 , one of each of th e

two pairs Of foliage - leaves ; I O,inflorescence ; 1 1

,large scale o f

opening bud with rud iment o f blade at th e tip 1 2 ,I 3 ,

I 4 , stagesin th e opening of a leaf-bud d .b, dormant bud ; f .b,

flow er -bud ;

l,lenticel ; l .b, leaf-bud ; l .s ,

leaf-scar ; r .b, rud imentary blad e ; s .s .

I —3 ,scale -scars .


These Observat ions help us to understand the true nature ofthe bud- scales . The upper , large, green ones are

,like those

of the Horse-Chestnut , leaf-bases bearing rudimentaryblades , while the lower , exposed ones are leaf- bases only .

Some of the earliest buds to open,however

, are larger thanthese and conta in flowers as well as leaves (Fig . 7 0 , 1

, f .b) .When fully expanded the blades are seen to be in one

piece (simple) , the five lobes not being divided into separateleaflets as they are in the Horse-Chestnut . Note also that

FIG . 73 . LEAF-MOSAIC OF SYCAMORE .

the leaves from one bud form an excellent leaf-mosaic

(Fig . By this means overshadowing and overcrowding

are reduced to a minimum, and the leaves secure fuller

advantages from exposure to air and sunshine .

Contrast the Sycamore Shoot with that of the Willow

(see Fig . and note that in the case of the latter , S imi lar

advantages are secured in another way , viz . by longinternodes and narrow blades .Beech — The bud of the Beech (Fig 74) presents several

interest ing differences from those we have examined .

Observe it s long,tapering form and the light -brown

membranous scales which are arranged in pairs . Remove


the outer scales and examine the inner ones carefully . You

will find between each pair a t iny green blade the outer

ones have no leaf- rudiment between them . Farther inwards are the foliage—leaves, folded fan-wise (Fig . and

the veins and margins are fringed with white hairs . Grow

ing out from the base of each leaf is a pair of light-brown

membraneous scales . Outgrowths of the leaf-base are called

stipules , and a carefu l comparison shows that the scales

of a Beech bud are such outgrowths , i . e . they are stipules .As the bud opens and the leaves mature , the scales, havingserved their purpose as protective structures

,commonly

fall off, and hence they are said to be deciduous . Thus

the leaves , when mature ,appear to be without stipules .

The bud - scales of many of our forest trees are stipules ,e . g . Poplar, Oak ,

Hazel, and Elm . In these cases,the

spring fall is one of st ipules , and not , as in the Sycamoreand Horse-Chestnut , of leaf-bases . In the case of a few

plants,e . g . the Laburnum ,

the scales do not fall when thebud opens, but wither on the branch . In many plants thestipules grow with the growth of the leaf, are green and

leaf- like, and last as long and serve the same generalpurposes as the leaf such stipules are persistent , e . g . Haw

thorn, Rose, Pea,

Violet , &c . Some plants do not produce

stipules, i . e . they are exstipulate .

The buds of some trees andmany herbs are not protected

by scal es at all, but are naked , e . g . Wayfaring Tree,Juniper

,

Barberry, Mistletoe ,Ivy, Bittersweet , &c . In the Way

faring Tree , however, the young leaves are protected bya mealy covering of star- shaped hairs , hence it is sometimescalled the Meal Tree .

Watch the buds of the Beech as they open in the spring

(Fig . 75 ) and compare the behavi our of the leaves wi ththat of the Horse-Chestnut leaves . Note the elongationof the bud , the separation of the scales

,the bright yellow

green leaves peeping above them, folded fan—wise and

FIG . 7 5 . OP ENING BUDS OF BEECH .

FIG . 76 . LATE R S TAGE OF OP ENING BUDS OF BEECH ‘

leaves pressed downwards by greater growth Of th e uppersurface .


of dwarf shoots with crowded leaves,while the buds at the

ends of the dwarf shoots of previous years have each developed several leaves , also crowded together, owing to theslow growth of their internodes . If you examine several twigsof the Beech , you will find that , while the end bud may growa foot or more in a season , a dwarf shoot may have grownonly three inches in ten or more years .S cots P ine — An excellent example of the development

of dwarf shoots is seen in the Scots P ine (see Fig .

Examine a small branch ,and you will find that i t is

terminated by a large bud , round the base of which are

three or four smaller lateral buds standing at nearly thesame level . Farther back the axis appears to be covered

by tough evergreen needle- leaves . Carefu lly examine theshoot to see where and how the needles arise . DO theyspring, likemany leaves we have seen, singly from the axisRemove a few of them . Do they come away singly, or inpairs ? Can you find any other structure on the axis stillremaining when the needles have been removed Examine

and compare with this , part of a branch from wh ich

the needles have fallen off naturally . What are the

structures producing the roughness of the shoot Are the

pairs of needles related in any way to S imi lar structures ?

If any doubt as to the last -ment ioned point remains , the

examination of an elongat ing bud in the spring will make

their relat ionship clear . The axis produces only scale ~

leaves . In their axils , buds arise which form very short

shoots (dwarf Shoots) . At the base of each are several

scale- leaves,and near the tip are two long, green needles .

Such short shoots are called bifoliar Spurs (see Fig .

They remain three or fou r years on the t ree, and are thenthrown Off . Each year new ones form

,so that the tree is

always green . Examine the ground under a pIne tree

and pick up a few of the old needles . Does the pine Shed

merely its leaves or its sh ort branches also We see that

BUDS AND BRANCHES 1 1 9

the short branches are shed as well as the needle- leaves,

and the scars left on the axis are not leaf- scars,but the

scars of dwarf shoots .Vernation or praefoliation.

— In the above examples wehave seen how neatly the leaves

are packed in the bud with theleast loss of space . Themanner

in which leaves are thus folded

and arranged is known as ver

nation or praefol iation , and

their relationship may be seenby the examination of a trans

verse section , or more easi ly by

a study of buds as they open in

the spring . Determine the ar

rangement ,manner of unfolding,

and direction Of greatest growth

as the blades expand , in the

following plants : the Dock and

Rhododendron , where the leaves

are back—rolled (revolute) the

Violet , Elder, Apple, Pear, andPoplar, where they are up—rolled

(involute) the P lum and Black

thorn where they are rolled from

one side to the other (convolute) ,and in the Ferns , where the

blade is rolled from apex to base

(ci rcinate) When revolute leavesexpand

, growth is greater on

the under surface in involute,

convolute,and circinate leaves

FIG . 77 . WINTE R SHOOTOF ELM .

— f .b, flower-bud ;l .b, leaf-bud l .s , leaf -scar ;

to scale -scars o f

th ree su ccessive years ; t . 1 to

t .4 , dead terminal buds of

four successive years .

growth during expansion is greater on the upper surfac e .

M onopodial and sympodial branching — Trace the d evelopment of shoots from the opening buds to the formation of


leafy branches and notice the variations in different plants .

In some trees, like the Sycamore , Horse-Chestnut,and P ine ,

the terminal bud cont inues the growth of the main axis

from year to year . single and continuous axis i s Called

FIG . 78 . BRANCH OF W ILLow .— d

, dead terminal bud .

a monopodium . In most trees,however , growth is not

so uniform ; usually the end bud dies and the lateralbud arising in the axi l of the next leaf below enlarges ,pushes thewitheredbud aside, and appears to be the terminalone . A careful study of the Ehn twig (Fig . 77) will makethese points clear . In the following spring this lateral


to twenty (see Figs . 70 ,1 89, If the growth of

the axis above such dormant buds is arrested by injuryor removal

,the dormant buds begin to grow into leafy

shoots . Thus old branches , and even trunks of trees , may

become covered with fresh Shoots .Shoots arising on the trunks of trees , usually from buds

which have long been dormant,are known as stool shoots

and are common on trees with a thin bark, e . g . the Lime .

They are a characteristic feature of the Elm, and occurfrequently on Sycamores , Oaks , and many other trees .New buds are occasional ly formed in the outer t issues

of branches and other members,e . g . on roots and leaves ,

and not in leaf-axils such buds are termed adventitious

buds . True dormant buds have a pi th continuous withthat of the branch , while the pith of adventit ious buds is

not continuous . Adventi tious shoots are common on the

roots of shrubs and trees , e . g . Raspberry (Fig . Rose ,

and P oplar, also on the roots of Dandelion ; while some

Ferns produce adventitious buds on their leaves .S hedding of leaves and branches — Having now described

the structure and behaviour Of buds , we may conclude thischapter with a reference to the shedding of leaves and

branches . The shedding of scale-leaves is a noteworthyfeature in the Spring , when , under Sycamores and Beeches ,the ground is covered with them . In the au tumn the

foliage-leaves are thrown Off and again the ground i scovered . Thus we have at least two leaf- fal ls in a year

(I ) A spring fall of scale-leaves and (2 ) an autumn fall

of foliage—leaves . From the P ine and often the P oplarwhole branches are thrown off . In addition there is the fall

of flowers , fru i ts , and their axes , so that each year a tree

sheds many of i ts organs .

HIBERNATION 1 23

CHAPTER X

HIBERNATION ; THE STRUCTURE OF MODIFIED

SHOOTS

HAVING gained the foregoing knowledge as to the struc

ture ,functions

,forms , and modes of growth of the vegeta

tive organs of a few common plants , we will now pay

attention to some that are peculiarly modified . In the

preceding chapter we have been studying the formation

of dwarf Shoots , rosettes , and scales— all of which are

cases of reduction . Occasional ly, however , the reverseoccurs , the roots , stems , or leaves becoming abnormal ly

enlarged ,in which case they usually act as storage organs

,

either of water, or organic food , or both . It is extremelydifficult , i f not impossible, to say how these modifications

were brought about , but we can often suggest some usefulpurpose they serve when once they are formed .

Adverse conditions and their efieot on growth — With thechanging seasons , plants are exposed to a great range of

conditions as to temperature, moisture, and l ight , which

greatly influence the power for work of the di fferent

plant -organs . The parts most exposed to these changes

are the Shoots above ground , the leaves being especially

sensitive . In temperate regions the winter conditions areunfavourable for active root -absorption

,and therefore for

active growth,as are the dry periods of many tropical and

sub-tropical countries . At the beginning of the adverseperiod the first changes we notice are the withering and

Shedding of the leaves of many shrubs and trees , and thedying down of herbaceous shoots . The strong trunks andbranches of the former persist , enveloped in their coats ofcork , whilst their buds are protected by tough

,brown

scales . But how do the more tender herbaceous plants


fare ? By what means do they tide over the winter ?

We know that many animals burrow in the ground beyond

the reach of frost and cold , and lie dormant until morefavourable conditions return . But do plants hibernate ?

and i f so , how ? Let us consider a few common species ,e . g . Shepherd’s Purse, Turnip, Daisy, Lily

,Bluebell ,

Crocus , and Iris , and note how they pass the wi nter .Annuals and ephemerals .

— The Shepherd’s Purse pro

duces a number of seeds in the summer, but when these are

shed the whole plant , roots and shoots , dies , and nothing

remains but the seeds . In the following spring the seedsgerminate, new plants are formed, which produce flowers ,frui ts , and seeds the same year and the plants , as before ,

die completely in the winter .

Species which thus complete their life-cycle in one

season are called annuals . They hibernate ei ther as seedsor

,less frequently, as fruits, and this is a very effective

method . Many of our common weeds of roadsides and

cornfields behave in this way , e . g . Groundsel , Chickweed ,Field Pansy

,Charlock ,

and Hemp Nettles . Some of these,l ike the Shepherd’s Purse,

may pass through their l ifecycle in a few weeks if conditions are favourable, so thatseveral generations may be produced in a season ; such

Short -l ived annuals are known as ephemerals, and

examples may often be found among the plants of

a waste-heap .

B iennials .

— The Carrot behaves differently . After theseed has germinated , the plant grows vigorously its root

enlarges considerably and becomes stored with a reserveof food-material s (see Fig . 26, In this condition itpasses the winter . On renewal of growth in the followingspring i t produces an abundance of flowers , fru i ts, and seeds ,at the expense of the food stored in the root

,which is

exhausted the seeds are shed and then the whole plantdies after two seasons’ growth To such plants the name


the roots l ike,and where do they originate ? Do these

agree with the roots we found on seedl ing plants of the

Wheat and Maize (p .

An examination of the underground parts of‘

theseplants convinces us that , ( 1 ) stems bearing lea

‘

ves (scal e

FIG . 79 . RH I z OME OF LILY OF THE VALLEY .— ( I ) b, end bud

emerging from th e soil ; 1 , withered leaf-bases ; so, scale -lea f .(2 ) section Of bud a , leaf-bases b, axillary bud which continuesgrowth .

leaves) with buds in their axils occur underground ; (2 )such plants may have not only underground stems butaerial stems also ; (3 ) the latter are in real i ty branchesof the former ; and (4) the fibrous roots spring from the

stem (often from the nodes) and are therefore adventitious .

STRUCTURE OF MODIFIED SHOOTS 27

Such -underground stems are known as rhiz omes that of

the Lily of the Valley (Fig . 79) is a very instructive

one to study . Observe the nodes with their scal e- leaves

and al so the branched fibrous roots springing from each

node in a circle . Such an arrangement of members istermed a whorl . Carefully dissect a bud and compare i t

step by step wi th the parts found in other buds you have

examined . Notice the di fferent kinds of scale- leaves :

the tough outer ones , forming a protective coat furtherinwards some which are rather fleshy ; then the fol iage

leaves . If the bud is a large one, l ook for the inflorescencein the centre. Which of these structures come above

ground ? How is the further growth of the axis continued

underground ? Compare this mode Of growth with that of

the Beech , Hazel , Elm ,or Willow . Is the axis monopodial

or sympodial The following examples of rhi zomes should

be studied and their parts compared : Garden Mint , Coltsfoot

,Dog’s Mercury, and Wood Sorrel . In all these cases

the end bud emerges from the soil,and growth is continued

underground by means of a lateral bud .

Rhi zomes as land-winners .

— The rhizomes of some plants ,such as the Marram- grass , Sand-sedge, and Horsetails

,

grow to a great length , often many yards, and thi s habitmakes them useful for reclaiming our sandy shores . Fig . 80

shows how the Marram-grass is planted on the sands .

Round the tufts wind-blown sand accumulates , and the

shoots by elongating keep their leaves above the surface .

Below the ground long rhizomes are formed , from the

nodes of which very long, slender roots arise and grow

deeply in search of water , the two producing a tangle,and serving effectually to hold the sand together . Atthe same time the old and decaying shoots , by adding

humus to the sand , begin the formation of a soil upon

which other plan ts can grow . S imilar uses are made of

rhizome-bearing plants to hold together the banks of


canals and railways -1 In these ways the undergroundparts of plants become valuable sand and soil -binders andplay an important part as land—winners

Thickened rhi z omes — Examine the rhizome of the'

3 0 1 0

mon’s Seal or the Iris . The axis is greatly thickened and

bears many branched adventitious roots ; the internodesare very short

,and the scale- leaves and buds are large .

Cut a slice across the rhizome and examine th e tissues .

Outside is a layer of cork , then a thick cortex,and

near the centre a number o f scattered vascular bundles .P lace on the cut surface a drop of iodine solution and notethe large amount of starch stored in the cells . As the plant

grows , the rhizome tends to rise to the surface of the

ground, and i f you examine Irises in a garden you willOften find that the soil is washed away from the rhizomes .

On plants whi ch have thus approached the surface, i t is

common to find thick unbranched roots which penetrate

the soil deeply , then contract and pull the rhizome downwards . Sometimes the growing end is directed downwards ,and as the rhizome elongates i t descends until a suitabledepth is reached . Fig . 82 shows such a descending rhizome

of the F lowering Rush as i t ploughs i ts way through themud in which i t grows .S tem- tubers .

—The P otato is another strangely modi fied

hibernating organ . On the surface, which is covered with

a layer of brown cork, are smal l depressions , the eyes

P lant a potato , or even a thick sl ice of potato, in a pot

of soil , and as it grows you wil l find that shoots spring from

the eyes a fact suggesting that they are buds . Fig. 83

shows a plant grown in this manner . From the eyes (e)leafy shoots have grown and the base of the stem has

produced numerous branched , fibrous roots . The buds

1 On railway banks these p lants Often ex tend th eir bounds,grow between th e rails , and produce a weedy track very difficu ltto keep clean .

FIG . 8 0 . MARRAM—GRAS S P LANTED AS A SAND - B INDER

FIG . 8 1 . RHI Z OME S OF S AND -SEDGE EXP OS ED BY THE WIND .

STRUCTURE OF MODIF IED SHOOTS 1 29

formed in the axils of the lower leaves have produced

branches (rh) which creep on the surface of the soil , and

you will Observe that they are swollen at the ends to formsmal l potatoes (t) , bearing eyes like the parent , one ofwhich is producing a shoot During the growth of

FIG . 82 . RH I z OME OF FLOWERING RUSH DESCENDINGINTO THE SOIL .

the shoots , the potato becomes soft and wrinkled as the

store of food is used up . Examine a potato and determine

the arrangement of the eyes note that at one end is a scar ,left when the potato breaks from the stem . Usually the

eyes are few or absent near the scar , become more numeroustowards the opposite or growing end ,

and are arrangedin a 3 spiral . In cul tivation ,

banking up with earth1 296 I


induces increased formation of rhizomes and tubers , but

i f left exposed to light , the tubers are small , green , and soondevelop leafy shoots . A potato plant , therefore ,

has three

FIG . 8 3 . P LANT GROWN FROM A SLICE OF P OTATO . .

— e eyeso.s , sh oot growing from an ey e of th e large tuber ; P

, slice o f

potato ; rh , rh izome ; t,tubers .

kinds of stems : (1 ) aerial stems , bearing green foliageleaves and flowers ; (2 ) rhizomes , bearing small scaleleaves ; and (3 ) from the rhizomes spring greatly swollenand i rregular stems on wh ich are reduced buds , the


FIG . 84 . THE CROCUS .

- I, Crocus corm 2

, corm wi th scales

removed ; 3 , vert ical section Of corm ; 4 , foliage -leaf d issectedfrom bud ; 5 , transverse section of foliage - leaf ; 6 ,

flower -bud

with sh eath removed ; 7 , corm bearing two flowering sh oots,

a young corm forming at the base of each ; 8 , flowering corm in

vertical section 9 ,base of corm 1 0 ,

young corm with contractileroot a , anth er ; a .r , adventitiou s roots ; b, axillary bud o . r , o .2 ,

o . 3 , corms o f successive years ; o .r , contractile root ; o .s , cormscar f , foliage - leaf P

,perianth s , spath e so, scale—leaf s .b,

sh eath ing base of foliage—leaf ; s .s , circu lar scale- scars st, stigma ;

ov, ovary v, veins .

STRUCTURE OF MODIFIED SHOOTS 1 33

leaves . Examine these carefully with a pocket lens .

Dissect off one or two leaves very carefully and note that

each is attached to the axis by a sheathing ring (Fig . 84,

Cut a leaf across the middle and examine the cut surface ,

and note the back- rolled margins and thick midrib

(Fig . 84 ,The cells covering the midrib are crowded

with starch grains which are used up as the leaf growsthese cells enlarge ,

lose thei r contents and become filled

with air they then reflect light from thei r walls and giverise to the familiar whi te streak of the adult leaf . In the

centre are three or more flower-buds each surrounded

by a thin,membraneous Sheath . Select one ,

remove the

Sheath ,and dissect the flower Outside is a short , six

lobed perianth (P ) , then come three stamens with short

filaments and large spear-Shaped anthers (a) . The ovary isinferior and three- lobed

,and above this is the long style

surmounted by three large,frilled stigma- lobes (3 st) . All

the parts of the flower are present and are easily made out

in the bud .

If flowering specimens (Fig . 84 , 7 and are examined ,

considerable changes will be noticed in the corm . At thebas e of the flowering shoots we see the beginning of a new

corm (8 formed by the thickening of the internodes

between the lower leaves . These leaves have becomewithered and dead , and thei r ring- like bases form mem

braneous scales around the young corm. The old corm

beneath (8 M ) , has given up much of its foodreserve of

starch , and eventually will collapse into a dead, shrivelledmass . Thus new corms arise as thickenings of the stem ofan axi llary bud of the old corm. In Fig . 84 , 8 this relationship is shown , but i n this case we can detect the collapsed

remains of the still older corm at the base Whenthe old corm is cast off , a scar is left (Fig . 84, 9 ) at the baseof the new one . This is a branch- scar , but , unlike theshoots previously examined , the new branch in the Crocus


lives on as the plant, while the old one dies away . Roundthis scar and at the lower nodes numerous fibrous roots are

given off in whorls (Fig . 84, 9 a .r) . S imilarly modified

stems or corms are met with in the Gladiolus .Ascent and descent in the soi l . Contracti le roots — Imagine

the Crocus repeat ing this process season after season , new

corms being continually formed on the top of those of theprevious year , and the mode of growth being a sympodium .

What wou ld be the posit ion of the corm in the soil at the

end of five or six years As each year’s corm is developedat a higher level than its parent , successive corms graduallyapproach the surface . Now it is found that many under

ground parts o f plants have what seems to be a sense of

depth and if circumstances result in their being broughthigher or lower than their normal depth in the soi l

,their

behaviour is such as to raise , or lower , the young growing

shoots as required .

The method adopted by the Crocus is one of whichnumerous examplesmay be found . Fig . 84 ,

1 0 shows a young

corm which was developed quite near the surface of the

ground ; from one sidefl

a long , very thick root (c.r) grew,

and pushed its way deeply into the firmer ground below .

Its upper part then shortened and thickened , producing

the wrinkles seen on the surface , with the result that the

corm was pu lled deeper into the soil . This process is

repeated by new root s in successive seasons until the requisite depth is reached . Such roots from their behaviourare called contracti le roots , and are by no means uncommon they may be found in the Li ly, Bluebell, Arum,

Dandelion,and other plants .

Bulbs and droppers .

—Compare the bulb of the Tulipwith the corm of the Crocus . Cut a specimen longitudinally , as in Fig . 85 , 1 , and note the parts of which it iscomposed . On the outside are the smooth ,

membraneous

scale- leaves and about four thick , fleshy leaves (s.2


two kinds of leaves ( 1 ) fleshy scale—leaves , and (2) foliageleaves . Unlike the corm, a bu lb consists mainly of leaves .A bulb of the Squ i ll , the Snowdrop , or the Hyacinth

should be compared with the Tu lip . In these also we‘

have

FIG . 86 ( I , 2, 3 , SUCCE S S IVE TRANS VERSE SECTIONS OF

TULIP BULB .— a , anth er ; f . I , 2 , and 3 , foliage -leaves ; g,

pisti l ;p, perianth s . l —5 , scale

- leaves st, stem .

two kinds of leaves , but the bases of the foliage- leavespersist , and become swollen with food- reserves , while the

green upper parts die away at the end of the season , leaving

a separat ion scar at the top of the swollen base . In the

Snowdrop, the Short stem produces two narrow , green

STRUCTURE OF MODIFIED SHOOTS 1 37

leaves and a flowering shoot , and the bases Of the leaves

thicken and store food,after wh ich the green portions die

away .

When diggi ng up Tu lip bulbs look out for curious forms

like the one shown in Fig . 85 , 3 . In this case an axi llary

bud has pushed its way through the old outer scale and

grown downwards in the form of a long , tubular , stalk- likebulb . A sect ion through this shows a small bud at the

lower end If such a bulb is carefully potted and

its behaviour studied , you wi ll find that adventit ious roots

are gi ven Off from the small bulb , foliageleaves grow out

into the air, and the tubu lar attachment to the parent bulbdies

,leaving a young bulb at a lower level in the soi l than

the parent .

Why should some buds remain Short and grow alongside

the parent bulb while others elongate and push their waydeeper into the soil Seeing that the buds are axillary

,

and therefore produced successively at higher nodes , whatwould be the position of the young bulbs in the soil after

several seasons’ growthIn consequence of this tendencv to ascend in the soil

,

bulbs would eventually come too near the surface for

successful development . We have seen various devices by

means of which plants maintain a suitable depth in the

soil,and the method adopted by the Tu lip is to produce

down-growing buds cal led droppers some of which ,especially in seedling plants , may be from three to nineinches long .

The means by which seedl ings of bulbous plants descend

in the soil and eventually reach the depth requisite for

successful growth may be well s tudied in the B luebell orW ild Hyacinth . In winter and in early spring many

s tages in the process can be found among the humus of the

woods , and a number are shown in Fig . 87 . You will find

that the blue-black seeds germinate freely among the dead

FIG . 8 7 . H IS TORY OF THE BLUE BELL BULB .—A

,B

,C,D

, germination Of th e seed and seed lings ; E ,

young bu lb ; F , G , H , I , L , d ifferentstages of elongation Of th e bu lbs and development Of contractileroots ; J , K , bu lbs again beginning to elongate ; o .r , contractileroo t ; cr .so, contract I le root -scar s , sli t in tubu lar cotyledon ;M , mature flowering bu lb l .so, leaf -scar .


stage the bu lb increases in s ize, and by the end of five or sixyears it has become a mature flowering bulb (m) . Afterwards the Bluebell reproduces itself in two ways : (1 ) bymeans of seeds

,and (2) vegetatively, by axillary buds

which form new bulbs close to the parent .

In bulbs the food i s stored mainly in the fleshy scaleleaves or leaf-bases . This food is used up in the Spring as

new leaves and flowers are formed the old scales collapseand die

,and form the d irty, shrivelled outer coverings so

familiar in bulbs .Geophy tes .

-The large food- store in bulbs, corms , and

rhizomes provides a ready supply upon which the plant

draws on the return of a favourable season for growth .

It enables the plants to bu ild up qu ickly new tissues and

complete the growth of the young organs packed in the bud .

Being situated deep down in the soi l ;‘

out of reach of the

frost , they are well protected , and many of these plants

are among our early spring flowers . In many cases they

d ie down early,having completed their work above ground ,

and after a short period of rest continue the format ion of

new organs in readiness for another year . Thus , much

activity goes on beneath the surface and unseen throughout

the greater part of the year, the actual period of rest beingmuch less than we might suppose from a study only Of theparts above ground .

P lants which pass so much of their time hidden in

the soi l are called geophytes (Gr . ge'

the earth , phy tona plant) . In temperate regions

,. the cold season is the

period Of hibernation . In tropical and sub-tropical regions,

hibernat ion occurs during the hot dry season .

Vegetative reproduction .

— Underground stems of thesevarious kinds provide very effective means of reproducing

the plan t and extending its range vegetatively . Those

with long rhizomes are well adapted to push along and

colonize new ground, like Quicks on a waste-heap or in

STRUCTURE OF MODIFIED SHOOTS 1 4 1

a neglected garden ,like Marram-

grass on the sandy coast ,or Bracken in the woods , each tending to occupy much of

the ground to the exclusion of other less- favoured plants .

Vegetat ive increase goes on not only by means of under

ground shoots , but to a very great extent by aerial shoots

as well . For example : a plant of S i lverweed (P otenti lla

Anserina) appeared in a garden and was allowed to grow.

It soon produced axillary runners l ike those of the Strawberry (Fig . and by the end of the season twelve runners

FIG . 88 . VEGETATIVE RE P RODUCTION IN THE S TRAWBERRY .

— New

p lantlets arising as ax illary sh oots on th e runners .

were produced with an aggregate length of seventeen yards ,and containing no fewer than 1 29 rooted plantlets .

Vivipary — In the case of several Alpine plants,especially

in wet autumns,a curious suppression of seed- formation

occurs . The embryo , instead of passing through a period

of rest in the seed , continues its growth uninterruptedly,

and on the inflorescence is borne a number of small plant letsinstead of fruits . These eventually drop off and reproducethe plant . Such plants are said to be viviparous (L. vivus

alive,paro I bring forth) .

Vivi pary occurs also in species of Leek and Garlic,and

the young bulb - like plantlet s on the inflorescence are called


bulbils Axillary buds somet imes drop off and form new

plants good examples are found in cu lt ivated species ofLilium and sometimes in the Lady

’

s Smock (Cardaminepratensis) . Reproduct ion by means of axillary tubers in

the Lesser Celandine has already been noticed (p .

A similar mode of vegetative propagat ion occurs in theWood Sorrel

,and examples may often be seen in the Oxalis

so common in greenhouses . In some Ferns, numerous small

plantlets are produced on the fronds by vegetative budding.

Social plants — Offsets and short axillary shoots form a

very effective means of spreading and give rise to densely

packed masses of plants which elbow out their weakerrivals . P lants of the same Species which grow in company

and cover a large patch of ground are termed soc ial species .It is by such means that the beautiful flowery cushions

of rock-plants are formed on the mountains,

and the

tussocks of sedges and grasses which produce the mono

tonous Cotton-gras s moors , and the gras sy swards of thehi lls and pastures

,and thus giy e rise to some of the

most striking features in the vegetation of a country .

The extensive tracts of Bracken in the woods and on thehill- slopes , the blue carpets of Wi ld Hyacinth ,

and lakesand canals choked by water-weeds , are a few examples ofthe spreading of plants over large areas

,not by seeds

,but

by vegetative means .

CHAPTER XI

MOVEMENTS AND ATTITUDES OF PLANTS

MOVEMENT is one of the common phenomena of li fe . We

usually look upon plants as stationary,and the power of

movement as characteristic of animals,but this is far from

a correct view of the case . Although a typical floweringplant is fixed to the soi l

,all its growing parts , roots as well


untvvine . Observe the di rect ion of twining in each case . The

stem of the Convolvulus,looked at from above

,twines from

right to left (contra- clockwise) . Most twining plants twinei n the same direction that of the Black Bryony

,however

,

twines from left to right (clockwise) . By this means suchplants are able to climb many feet above ground ,

and to

reach the air and sunlight without the expenditure ofenergy required in building up strong erect stems .

Climbing organs sens itive to contact. Tendri ls .

— In the

W hi te Bryony (B ryonia dioica) (Fig . Clematis (Fig .

Bush Vetch (Fig . and Sweet-Pea (Fig . slenderclimbing organs called tendr ils are developed ,

which differfrom Climbing stems in being sens itive to contact .The Passion F lower has very sensitive branch- tendrils

whose movements are eas ily observed . Fig . 93 shows theresult of an experiment with one such tendril . At p m .

the concave s ide of the tendril was gently stroked witha slender stick and records of i ts movements were taken

,

with the result shown in the diagram . If,in describing

such a spiral , the tendril meets with a support , it twines

round this support and clings firmly. Spiral growth

continues , but being now fixed at both ends,the tendril

soon develops a reversed spiral . That this form of spiralShould be produced can be easily understood if you fixa piece of string at both ends and turn the middle port ion

the part on the right turns in the Oppos ite direction to

that on the left . Tendrils showing the reversed spiral are

also seen in the Whi te Bryony (Fig . The tendrils of

the Vi rginia Creeper (Fig . which are also modified

branches,are peculiar in that they move away from the

light (negatively heliotropic) . At the free ends disks

are formed ,which

,when stimulated by contact wi th

a rough surface ,become coated with mucilage and are

thus cemented to the support .Tendrils are sensitive thread- like plant organs by which


FIG . 9 5 . SHOOTS OF GOOSEBERRY .— 1 ,

position of leaves in th eshad e 2

, in th e sunligh t P leaf-base prickles ,

MOVEMENTS AND ATTITUDES OF PLANTS 1 47

a plant fixes itself to a support . They may be modifica

tions of ( 1 ) branches , e . g . Passion Flower, Vine , Virginia

Creeper, and Whi te Bryony ; (2 ) leaves , e . g . the Chick-Pea

(3) petioles , e . g .Clematis ; (4) leaflets , e . g . Sweet -Pea,Vetch

,

and Garden Pea ; or (5 ) stipules , e . g . some species of Smilax .

Sun and shade posi tions — If you note the differences of

position of leaves in sunny places and compare these leaves

with others of the same kind growi ng in the shade , you will

see that they take up a favourable position with reference

to light . Fig . 95 shows two shoots of Gooseberry takenfrom different sides of

'

the same plant . One (I ) was overshadowed by branches of an apple-tree

,and exposed its

leaves fully to the available li ght . The other (2 ) was notovershadowed , and its leaves moved in such a way as to

expose the edges of thei r blades to the direction of the sun’s

rays . As ct I Ophyll is decomposed by strong sunlight ,it is an advantage to a plant organ to assume a position

whereby the smallest surface is exposed to the direct raysof the sun .

F ixed light posi tion — Some Acacias (Fig . 96, 1 ) growingin sunny regions have curiously modified leaves , whichpersistently turn thei r edges to the sky and give a characteristic appearance to the plants . The blades are not

developed , but the leaf—stalks are flattened out and become

leaf- like, and are called phyllodes . The atti tude assumed

by the foliage of a plant with reference t o light is calledthe fixed light position In some plants the leaves arereduced to scales

,the stems flatten out

,resemble leaves ,

and,as in the Acacias

,turn thei r thin edges to the sky .

Such leaf—like stems are known as phylloclades,and occur

in the Butcher’s Broom . Other examples are the Smilax

(Myrsiphy llum) (Fig. 96, 2 ) and species of Asparagus .

Extraordi nary examples occur in Cacti (Fig . 96, 3) and

other desert-plants . The huge fleshy stems are green,

store a large supply of water,and do the work of foliage

x 2


leaves . The leaves are often reduced to stiff, radiating

spines (l .s) forming a gauze- like covering to the surface,

which acts as a most effective light-screen and protects

the chlorophyll of the stem from the too powerful rays of

the sun . Thus,sunlight is an important factor in deter

mining the position of stems and leaves,and there a

FIG . 96 . S TEMS WHICH PERFORM THE FUNCTIONS OF LEAVE S .

1,Acac ia ; 2

, Smilax ; 3 , Cactus ; l .s , leaf-spines P,leaf-like

petioles (phyllodes) P o, leaf-like stem (phylloclade) ; s .l , scale

leaf .

tendency for plants growing in dry and very sunny placesto take on strange shapes and exhibit curious devices whichhelp the plant to survive under trying conditions .

P rotectivemovements againstradiation and transp irati on .

Movements which have for thei r object reduced radiationand transpiration are also very common . Note how young

leaves emerge from the buds in spring in, e . g . , the Elm

(see Fig . 1 98, Beech (see Figs . 75 and Lime,and

H orse-Chestnut (see Fig . At first they are erect,then

as they unfold and grow they bend over and hang downwards with thei r under surfaces applied one to another so


middle leaflet now bends over them,folding the two sides

of the blade downwards and exposing the back of its midribto the sky. The amount of leaf- surface exposed to radiation is thereby greatly reduced

,and in keeping with this

,

the l ower and more exposed leaf- surfaces contain fewerstomata than the upper and more protected ones . Duringthe day Clover leaves form an excellent mosaic

,but at night

,

when the leaflets are tucked in, the smallness of the space

they occupy is very striking.

Compare with the Clover leaves those of W ood Sorrel

FIG . 98 . WHITE CLOV E R .

— I,trifoliate leaf , day -position 2 ,

nigh t -position m, motile organs ; 3 , 4 , and 5 , inflorescences of

Clover the flowers turn downwards after pollination .

(Fig . 99) or a common garden Oxali s . In these plants thethree leaflets droop at night , hang vertically , apply theirmidribs to each other, and so expose their upper and

protect their under surfaces , to which the s tomata are

restricted . They thus secure protection against cold, butby a different method from that , of the Clover . If these

plants are placed in the dark at midday they do not close

their leaves until the proper time their habi t of going to

sleep at definite times has become fixed,and it takes some

days for them to become accustomed to changed hours .Such movements are known as s leep -movements .The False Acacia (Robinia) furnishes another example

of motion in plants,and i ts leaf-movements should be

M OVEMENTS AND ATTITUDES OF PLANTS 1 5 1

studied . Each leaf is pinnate,i . e . with leaflets arranged

on each side of the midrib like the pinnae of a feather .

FIG . 99 . WOOD SORREL .—a ,young leaves as they first Open ;

b, day -position o f leaflets ; c , n igh t -position ; d, bases of leaflets

enlarged ; e , f , g ,movements o f growing flower- stalk ; h , bu lbils

in th e ax ils Of leaves ; i , vertica l section of a bu lbil m,motile

organs r , rhi zome .

A leaf of the False Acacia ,l ike most pinnate leaves , ends

in a single leaflet . At the base of the leaf are two stipules

transformed into spines . During the day the leaflets are

horizontal,but in intense sunlight they move upwards ,


apply their upper surfaces each to the opposite one ,and

point thei r tips to the sky . At night they droop and applytheir under surfaces together . Thus they obtain the

advantages of favourable light , escape the injurious effectof intense light , and , on assuming the night-position , reducethe loss of heat from radi ation .

Rap idmovements inS ensitiveP lants — Some plants exhi bitthe power of movement to such a degree as to have earnedthe name of Sensitive P lants . The most familiar exampleis M imosa pudi ca, the Sensitive P lant . Its leaves are

bipinnate, i . e . each leaflet or pinna is again pinnately

divided into similar segments or pinnules . The end of eachleaflet has a pair of pinnules . At the base of each leafletand pinnul e, and also at the base of the leafstalk

,there is

an organ of movement , and the leaves exhibit sleep—movements such as are seen in the Clover and Wood Sorrel .

So sensitive are the leaves,that a very S light stimulus

causes the leaflets to droop in the daytime . If a lightedmatch be held under the end of a leaf , the heat- stimulusproduces a series of remarkable changes . Not only do the

heated pinnules droop , but the stimulus is transmi t tedfrom one to another, pinnul es and leaflets drooping in

succession,until

, eventually,the stimulus

,reaching the

cushion on the leaf-bas e, the whole leaf hangs down lan~

guidly . There i t remains until the shock has passed off,

when it gradually regains its former pos i tion . The leavesof the Venus ’Flyt rap close up in a similar manner, but veryrapidly

,in response to a contact—stimulus (see p .

These movements are due to rapid changes in the tur

gidi ty of the cells of the cushions the effect of a stimulus

is to cause water to escape from the turgid cells of the

cushion into the neighbouring ai r—spaces . Later, as the

cells oncemore become turgid,the leaves and leaflets resume

their awake position .

M ovements of flowers and fruits . Flower-movements


flowers of the Evening P rimrose as they open on a warmsummer’s evening . Fig . 1 0 0 shows the stages observed

in two flowers . The calyx slips down on one s ide and the

four free tips curve back and reveal the rolled-up petal s .

The corolla unscrews at the base , causes the calyx to splitmore and more

,and as the petal s unroll

,the mouth of the

corolla Opens and the stigmas appear . The calyx now

Splits at the bottom,the sepal s suddenly turn backward ,

or inside out , wi th a distinctly audible click,and the

crinkled petals unroll,slide over one another, and soon ful ly

expand . The sound produced resembles that of two sheets

of paper, one glidi ng over the other . If we look at the

stamens we find that the stringy pollen is already hangi ng

out of the anthers , while the stigmas,not yet ripe, spread

out thei r four lobes well above them . As many as a dozen

flowers may be seen to open in this way on one plant inhalf an hour.The various attitudes that flowers assume should be

carefully observed under the following conditions (1 ) inbud

, (2 ) in flower , (3) in sunshine , (4) in cloudy and wet

weather, (5 ) during the day , (6) at night , (7 ) as the frui tripens , and (8) when the frui t is ripe. Figs . 1 0 1 and 1 0 2

Show the movements of the flowers and fruits of theW i ldHyacinth . Not ice that the flowers are erect in bud laterthey turn away from the axis

,expand and hang downwards ,

the lowest and Oldest opening first . After pollination theybecome erect again , whi le the fruit- stalk lengthens and

becomes rigid . In the W hite Clover (see F ig . the

flowers are erect in bud ,horizontal in flower

,and after

fertilization hang downwards . The W ood Sorrel (see Fig .

99) droops both at night and in dull , damp weather ; it is

erect in fine,sunny weather

,droops as the seeds ripen , and

is again erect in fruit .Fig . 1 0 3 shows the movements of the parts in an Opening

inflorescence-bud of the Horse-Chestnut .

FIG . I OI . FLOWER -MOV EMENTS OF WILD H YAC INTH .

FIG . 1 0 2 . FRUIT-MOV EMENTS OF WILD H YAC INTH .

F IG . 1 0 3. THREE S TAGES IN THE OP EN ING OF THE TERM INALINFLORES CENCE -BUD OF H ORSE - CHE S TNUT .

FIG . 1 0 4 . DANDELION .

— Th e stalks Of th e Open flow er—h ead s

are erect after po llination th e h eads close up and th e sta lk bendsover to th e ground .

PART II

THE REPRODUCTIVE ORGANS

CHAPTER XII

BIOLOGY OF THE FLOWER . DICOTYLEDONS

I . P ollination of S imple F lowers by W ind and Insects

IN the study of buds , corms , and bulbs , we have become

familiar with the facts that Shoots are frequently condensed

that the internodes , instead of elongat ing,remai n um

developed ; and that , in consequence , a number of leaves

spring close together from the Short axis . Some of theleaves arise singly and are arranged in a close spiral

,whi le

others stand two at a level,in crossed pai rs .

Theflower a condensed and modified shoot — In our examination of the Stock flower we found something very S imi lar ,viz . a condensed or dwarf Shoot

,with a tendency for the

flower- leaves to arise close together in crossed pai rs . This

condensation is characteristic of flowers,and i t is interesting

to note how frequently flowers arise on dwarf,leafy Shoots ,

or spurs,as in many frui t- trees . This shortening of the

axis,together wi th the great modification that has taken

place in the s ize, shape,colour

,and function of its parts ,

distinguishes a typical flower f rom any other part of theplant .

Flowers , however, have not arisen in this simple wayf rom a leafy shoot . It is more probable that stamens and

BIOLOGY OF THE FLOWER 1 57

carpels , or thei r equivalents , came into existence first , and

that petals , and perhaps sepals , were derived from them

by modification of thei r parts , as,

may be seen in double

flowers like roses , and in the W hite W ater-Li ly (Fig .

Very ancient flowers hadmany stamens and carpels arranged

spirally on the axis, but in modern flowers the parts are

fewer in number and usually arranged in cycles or whorls .

General ly the flowers appear towards the end of a season’s

activities . In an annual they herald the closing scenes o f

its life- cycle and provide for the formation of fru its and

seeds , which will soon be all that remain to perpetuate the

race . In some cases flowers appear early in the season and

FIG . 1 0 5 . STAMENS OF WATE R -L ILY,S HOW ING TRANS I TION

FROM S TAMENS To P E TALS .

before the leaves , as in many trees, and i n the Coltsfoot ,

Wood Anemone ,and many other herbs . In the Autumn

Crocus , or Meadow Saffron (Colchicum autumnale) , on theother hand ,

the leaves complete thei r work and die down

before the flowers appear . Whether early or late, however ,the chief object of the flower is to produce frui ts containing

seeds , which ,on falling to the ground , may produce a new

generation and all the parts of a flower di rectly or indirectlys erve this end .

S tructure and functions of the parts of a flower — The fourparts of a typical flower are usual ly arranged in successivewhorls on the short axis

,which is known as the receptacle .

The lowest and outermost is composed of small green sepals

1 58 THE REPRODUCTIVE ORGANS

which form the calyx,and which in the bud completely cover

and protect the other parts . The second whorl— the corolla— consists of brightly- coloured petals

,which are often

scented,and sometimes bear honeysecreting glands . In

consequence of thei r colour,scent , and honey

,they are

attractive to insects . The two inner whorls di ffer from

the outer ones in an important respect . They bear repro

ductive bodies called spores such spore-bearing organs

are known as sporophylls . The whorl of sporophyllslyi ng immediately wi thin the corolla is the androecium

,

and consists of small-stalked bodies,the stamens . Each

FIG . 1 0 6 . TRANS VERSE SECTIONS OF ANTHERS .

1, before ; 2

, after dehi scence P o, pollen-

grains .

stamen has a slender stalk or filament,bearing on i ts free

end the anther this consists of four parallel pollen- sacs

(Fig . or m icrosporang ia (Gr . mi kros small , sporaa seed ,

angeion a case) , wi thin which are a large numberof pollen-

grains or spores (P o) , whose production is thespecial funct ion of the stamen . These minu te spores arecalled m icrospores , and the organ which bears them (thestamen) is the m i crosporophyll (Gr . phy llon a leaf) .In some flowers the stamens are attract ive in colour

,and

the pollen is an important food for bees and other insects .

The uppermost part of the axis gives rise to sporophylls

of a different kind , the carpels , which together const itutethe gynoecium ,

or p isti l . Usually three parts of the


Many of our forest trees produce S imilarly reduced flowers .

This arrangement , in which the stamens and the pist ils arein di fferent flowers but on the same tree, i s cal led monoe

clous (Gr . monos one,oikos a house) . Such fl0wers

are inconspicuous and unscented , and the staminateflowers produce a large quanti ty of pollen which is loose ,

dry,and light , and easily carried by the wind to the large

stigmas of the pistillate flowers . In theW i llow s (Fig . 1 85 )and P oplars (Fig . 1 86) the two kinds of catkins are borneon different trees , and this arrangement is called dioecious

(Gr . di two) . In all such cases the pollen carried to thestigma comes from another flower,and when this occurs the floweris said to be cross-pollinated . InWillows the stamens are brightyellow and numerous , and each

flower contains a honey-gland or

nectary at the base. Insects oftenvisi t these catkins and collect from

FIG . 1 0 7 ‘ R IPE S TIGMAS them both honey and pollen,with

OF MALLOW CURLING which their bodIes may become

AMONG THE ANTHERS dusted . Thus the pollen may be

carried to a pistil -bearing catkin

and some of i t deposited on the stigmas .

From the abundance of fruits produced by such treesit i s obvious that simple and unattractive as the flowers

are ,they yet contain all that is essential for frui t-produc

t ion . Hence stamens and pistil are spoken of as the

essential organs of the flower . In the flower of the S tock

other parts are present , viz . the sepals , which are protective,and the petals , which are attractive . Both parts are use

ful , but , as we have seen ,not essential , for the production

of seeds .

S elf-pollinated flowers — In the flower of the Round

leaved Mallow (Fig . 1 0 7) there are five free sepals and

BIOLOGY OF THE FLOWER 1 6 1

five free petals ; the stamens are numerous , but thei rfilaments are al l joined to form a tube round the pistil ,hence cal led monadelphous (Gr . adelphos brother) . Thepistil is superior

,the carpels numerous and syncarpous .

There are many long stigmas which , i f not cross-pollinated ,

grow ,curl over among the anthers

,and thus receive pollen

FIG . 1 0 8 . MODIFICATIONS IN THE MOUTH -PARTS AND LEGS OF

INS ECTS WHICH COLLECT H ONEY AND P OLLEN FROM FLOWERS .

P o , pollen grains (after Sharp and M ii ller) .

from the same flower . By this means sel f-pollinati on takes

place .

F lowers attractive to,and pollinated by , insects — Flowers

whi ch develop bright colours , scent , or honey ,attract large

numbers of insects , which feed on the honey and pollen1 296 L


and many of the modifications found in flowers are paralleled by modifications of the mouth-parts of insects

(Fig . The mouth-parts of the S impler insects, e . g .

beetles and flies , are so short that they are unable to -reach

the honey unless i t is exposed in an open,shallow flower .

Honey in a deep tube is inaccessible to them, and onlyinsects with mouth-parts elongated to form a proboscis areable to reach it . Some flowers have tubes several incheslong (8 to 1 0 inches) , and there are insects with probosceslong enough to obtain honey from the bottom of them .

I nsect pollinators ‘

and their mouth-parts .

— Fig . 1 0 8 shows

the mouth-parts of various insects which visi t flowers .1 is the head of a beetle (S trangalia attenuata) which can

l ick honey from Shallow flowers 2 , the head of the DroneFly (Eri stalis arbustorum) with an extensible proboscis ;

3 , the head of a fly (Rhingia rostrata) , in side view ; 4 ,the proboscis fully extended ; 5 , the mouth-parts of the

Long-tongued Bee (Anthophora pi lipes) 6 , the end of theproboscis enlarged to show the honey- spoon 7 , the

Honey Bee (Ap i s mellifica) with masses of pollen (P o) onthe hind legs 8

,the hind leg of a bee with mass of pollen

9 , collecting-hairs on the leg of a Honey Bee ; 1 0 , a hai rmagnified, with pollen-

grains attached ; 1 1 , proboscis of

a moth,which is very long and coiled up l ike a watch

spring .

Such insects perform unconsciously a valuable service in

carrying,on their bodies , pollen from the anther to the

stigma, and their habit of visiting flowers for food hasprobably been an important factor in the evolution of manyflowers . On the other hand , the insects have themselves

become modified, especially in the organs surrounding the

mouth .

I nsects , useful and i njuri ous — In the mature stage , insects are

Often very usefu l to flowers , and in many cases seeds can onlybe developed wh en insects act as pollinators . I t i s during thi s


Of flowers to determine the chief devices for securing pollination and the part played by insects in bringing i t about .P ollen—flowers s impleforms visited by insects f or pollen .

—The Clematis or Traveller ’s Joy (Fig . 1 0 9) has a calyxconsisting of four greenish-white sepals which resemblepetals , hence said to be petaloid . There i s no corolla ;the stamens are numerous and arranged below the pistil

,

not in whorls , but spirally . The pistil consists of manycarpels which are free from one another

, and are hencesaid to be apocarpous (Gr . apo from) . The flowerssecrete no honey, though they provide much pollen fortheir insect visitors .

In the W ood Anemone (Fig . 1 1 0 ) the flowers appear

before the leaves but below the flower is a whorl of threelarge green , leafy bracts . The calyx consists of five petaloid sepal s which are pinkish-white and conspicuous

, and

act as petals , the corolla being absent . The stamens

are numerous (indefinite) , and arranged spirally below thepistil

,which consists of many small , spirally arranged

carpels , free from one another . Examine flowers of di fferent

ages , and—

notice the order of ripening of the stamens andcarpels . The outer stamens open first , the stigmas being

covered by the inner ones . There is no honey in the flower ,but i t i s visi ted for pollen by insects which alight in thecentre, carry pollen from the anthers on to the ripe stigmas

of an older flower, and so bring about cross—pollination .

Later , the younger stamens and the stigmas are ripe together,and self-pollination may occur .The Marsh Marigold (Fig . 1 1 1 ) is a S imilar flower with

a large attractive calyx of five or more yellow sepal s . The

stamens are numerous and open outwards ; the carpels arefree, and each contains several ovules . On the sides of eachcarpel and near the base are two shallow depressions where

honey is secreted . This is an additional attraction forinsects . Notice the curious stipule (st) , which is quite

FIG . 1 0 9 . FLOWERING SHOOT OF TRAV ELLER ’

S JOY .


entire in the bud and encloses the young leaf . As the leaf

grows it bursts through the stipule, which remains as a thin

membrane surrounding the stem .

The Buttercup (Fig . 1 1 2 ) has five free sepals (polysepalous) , and alternating with them are five free petals

FIG . I I I . MARSH MARIGOLD .—cd , calyx ; st, stipu le .

(polypetal ous) . Examine the bases of these and note thehoney-glands . The stamens are numerous (indefinite) ,and arranged spirally below the pistil they ripen beforethe carpels, and in succession from without inwards .The l ower stamens first turn outwards and conceal the


FIG . 1 1 2 . I , TUBE ROUS BUTTERCUP ; 2 , petal removed ; 3 ,

vertical section of flow er ; a , stamen ; br , bract ; c , carpel ; ca ,

reflexed sepal ; n, nectary ; P, petal r, receptacle ; t, tuber.


nectari‘

es and shed their pollen on the petals , not on the

stigmas , which are not yet ripe . The pistil is in the centre,and consists of many spirally-arranged, free carpels , eachcontai ning one ovule . As in the Clematis , Anemone , and

Marsh Marigold, the pistil is apocarpous and superior .Such flowers , in which the sepals , petals , or stamens

are fixed bel ow the pistil , are said to be hypogynous .

The Buttercup provides both pollen and honey, but inorder to obtain the latter , insects must first push aside the

C B C.‘

Ga . 9 '

FIG . 1 1 3 . FLOWE R OF STRAWBERRY .—I

, back of flower, showingth e five sepals (ca ) and five smaller stipu les (st) alternating withth e sepals ; 2 , flower in vertical section ; a , stamen ; o, carpel ;ca , sepal g , upgrowth from centre Of receptacle bearing the carpelsP , petal r , expanded and hollowed receptacle ; s t, stipu le .

stamens,and in doing so their bodies become dusted with

pollen . If they now vi sit older flowers where the stigmasare ripe, they may deposit on them some of this pollen .

The different kinds of buttercups should be examined and

their differences observed .

P erigynous and ep igynousflowers the S impleflower-tube.

— The Strawberry (Fig . 1 1 3) has five sepals and five

sepal - like s tipules , the latter forming what is cal led an

epicalyx. The flower thus appears to have ten sepals .

These, together wi th the five alternating petals and numer

ous stamens , are borne on the edge of an expanded and


In the Rose (Fig . 1 1 4) the receptacle is hollowed deeperstill , and arising from the edge of it are five reflexed sepal s ,five petals , and numerous stamens , all of which are peri

gynous . Wi th in the cup and fixed to the S ides are Severalfree carpels, each containi ng one ovul e. NO honey is

secreted, but the stamens provide much pollen for insects .The Rose and Clematis are therefore cal led pollenflowers .

The flowers of the Cherry (Fig . 1 1 5) and P lum havea receptacle which is hollowed , and on its edge are five

sepals, five petals, and numerous stamens (i . e . they are

FIG . 1 1 5 . FIG . 1 1 6 .

VERTICAL SECTION ,VE RTICAL SECTION ,

FLOWE R OF CHERRY . FLOWER OF AP P LE .

perigynous) . There is only one carpel , and this is superiorto and free from the receptacle- cup . The anthers and thestigma ripen together ; the anthers of the Shorter inner

stamens and the stigma stand at the same level,while the

outer stamens are longer and overtop them . Honey issecreted by the receptacle-cup ,

and insects collecting honey

and pollen may touch the st igma with pollen brought from

another flower,and thus bring about cross-pollinat ion but ,

owing to the relat ive posi tion of the anthers and st igma,

self—pollinat ion will very commonly occur . The whole of

the fruit i s formed from the carpel ; the receptacle-cup

is thrown off and does not form part of the fruit .

BIOLOGY OF THE FLOWER 1 7 1

In the Apple (Fig. 1 1 6) and Pear the pisti l consists offive carpels , which are syncarpous and closely united to

the hollow receptacle ; the five sepals, five petals , and

numerous stamens are thus carried on to the top of the

ovary (i . e . the flowers are epigynous ) . Owing to the

union of the five carpels with the receptacle- cup the honeyis easily obtained

,and the flowers are visited by a great

variety of insects . The five stigmas are prominent , ripen

before the anthers , i . e . they are proterogynous (Gk . proteros

before) , and so favour cross-poll ination . If insect -V isits

fail, pollenmay be shaken or may fall on to the stigmas thisis aided by the horizontal posit ion of the flowers . After

fertilizat ion the receptacle enlarges and forms the fleshy

part of the fruit . The five united carpels form the core

(FigExamine old fertilized flowers of the Strawberry, Rose,

Cherry, and Apple, and note in each case themode of origi nof the fruit and the structures concerned in their format ion .

Tubular flowers with concealed honey . Devi ces to secure

cross-pollination.

— In the S tock (Fig . 3 , 1 ) the four uprightsepals form a narrow but split tube, which conceals thenectaries found at the base of the two Short stamens .The stamens here

,unlike those of the previous flowers , are

reduced to six . Such a deepened flower- tube will prevent

the short- tongued insects from securing the honey, but this

can easily be Obtained by the long-tongued insects, such

as moths , butterflies, and bees . These insects are moreintelli gent and better adapted for carrying pollen fromanther to stigma than the short - tongued insects , like beetlesand flies , which may take pollen and honey from shallowerflowers with less l ikelihood of brIngIng about pollinat ion .

Those flowers , therefore , which attract the more intelligent insects possess a double advantage : (1 ) they needless pollen , and (2) cross-po llination is more certain . Let

us see by what means these advantages are secured insome other flowers .


In the Geranium the calyx has five sepals j oined bytheir edges to form a deep tube . A united calyx is said tobe gamosepalous (Gr . gamos un ion) . The five petalsare free there are ten stamens

,five outer and five inner .

At the bases of the five outer ones are nectaries . It i s

interesting to watch the movements of the stamens in theF ield Geran ium . When the flower opens

, the stamens lieon the petals ; they then raise themselves parallel to thepistil , shed their pollen , and return— first the outer set , thenthe inner— to their former posit ion . The pisti l consists

FIG . 1 1 7 . 1 , FLOWER OF FIG . 1 1 8 . FLOWER OF GAR

GARDEN GERANIUM 2, trans A DEN NAS TURTIUM .

- n , honeyverse section of pedicel and secreting spur ; P ,

ped icel .nectary ; n ,

nectary P,ped icel

of flower.

of five superior , united carpels . When the pollen is Shed ,

the stigmas ripen and spread out as five lobes to receive

pollen from another plant . Stamens which ripen before the

pist il are said to be proterandrous .

Compare with this the Garden Geranium (P elargonium)(Fig . In this

,do the stamens of the stigmas ripen

first In these flowers cross—pollination is secured by the

stamens and the pistil , which , though existing in the same

flower,ripen at di fferent times . Look for the long tubular

nectary which adheres throughout its whole length to theflower-stalk . The presence of the nectary in the Pelar


lastly the two inner ones , which are the smallest . Alternating with these are five stam ens

,which shed their pollen

before the stigma is ripe . These three whorls,unlike the

preceding examples,spring from the top of the o vary

,

and hence are said to be epigynous . The pisti l consistsof two uni ted carpels inferior to the other whorls . On

the top of the ovary is a honey~secreting disk (d) , whichsurrounds the two stigmas , and these ripen only when thepollen of the same flower has been shed . The honey isfreely exposed and liable to be spoiled by the rain , and

may be obtained by short- tongued insects which commonlyvi sit the flowers . In this cas e conspicuousness is due to

the aggregation of many small flowers at the same level in

the inflorescence, and by the outer petals enlarging at theexpense of the inner ones .The Buttercup

, S tock , S trawberry, Rose ,Geranium

,and

Chervil al l agree in one important respect— thei r petals arenot joined

,i . e . the corollas are polypetalous . In most

cases the sepal s also are free . In the Geranium , however,they are united , and the calyx is gamosepal ous . Theseflowers also show di fferent methods of forming the flowertube

,namely : (a) by erect sepals

,as in the S tock ; (b) by

a hollow receptacle,as in the S t rawberry and the Rose and

(o) by united sepals , as in the Geranium .

CHAPTER X I I I

BIOLOGY OF THE FLOWER (Continued)

II . P ollinati on of Tubular and Highly Developed Flowers

THE flowers we have considered above are general ly

S imple in structure . Flowers pollinated by the wind have

no perianth,or only a very rudimentary one ; they are

smal l and inconspicuous,and produce much pollen and

the stigmas are large , branched and sticky,to catch the


pollen,much of which is wasted . Flowers possessing a

perianth may have only a single whorl,and this is often

petaloid . In those with a double perianth- a calyx

and a corolla— the latter is usual ly attractive . In the

lower types the parts are free, the flower-cup is more or

less open , and the pollen and honey are very accessibleto insects . In various ways , however, a flower- tube is

developed in higher forms which protects the honeyfrom rain and excludes the lower types of short-tonguedinsects .We have now to consider a

further stage in the development

of the flower—tube and its relation

to the habits and structure of the

higher and more intelligent types

of insects .

Tubularflowers wi th unitedpetals .

—The Cross- leaved Heath has five

united sepals and five petals j oinedby their edges to form a tube ;

CROS S -LEAVED H EATH .

the corolla Is thus gamosepalous . P 7 , anth ep pmcesses ; st,

Within the bell- shaped corolla (Fig . stigma ,

1 2 0 ) are the stamens , which are

peculiar . Each anther has two long processes or arms ,and these proj ect outwards towards the corolla-wall . Near

the top of each anther are two pores , through which the

pollen escapes when ripe . The pist il is superior and

syncarpous , and around its base is a ring-like nectary ;the style is long and proj ects beyond the anthers to the

mou th of the bell . An insect visiting the flower will

bri ng i ts head against the s tigma and ,in pushing its

proboscis into the flower to obtain the honey, touch the

anther- processes , which , acting as levers , will separate the

anthers and cause a shower of pollen to fall on to

the head of the insect . The tube is too deep for the

FIG . 1 2 0 . FLOWE R OF


short-tongued insects : the chief visitors are bees , lepidOptera ,

and long-tongued flies . The flowers of the Heathshang downwards

, so that the honey is protected fromthe rain .

Difl'

erent kinds of flowers in the same species .

— In the

P r imrose (Fig . 1 2 1 ,1 ) and Cowsl ip (Fig . 1 2 1

,2 ) the five united

FIG . 1 2 1 . I , THE P RIMROS E ; 2 , COWS LIP ; 3 ,long-styled form

4 , short-styled form br , bracts .

petals form a long, narrow tube surrounded by an inflated

calyx of five united sepals . If a number of flowers are

examined , two kinds will be found : one with the knob- likestigma at the mouth of the tube and the anthers half-waydown (Fig . 1 2 1 , and the other with the five stamens at themouth of the tube and the stigma half-way down (Fig . 1 2 1 ,


Outside is a series Of small bracts resembling a calyx

and known as the involu cre . Within this is a series of

small flowers which resemble a corolla,but on careful

examination each is seen to consist below of a small inferior

ovary the calyx is absent the corolla of five petals forms

a narrow tube below ,and spreads out above in the form

of a white pink- tipped strap . Such

a strap-Shaped corolla is said to be

ligulate . There are no stamens , but

the style has two branches with

out hairs . These very smal l strap

Shaped flowers are called ray -florets

(Fig. 1 22 ,The yellow disk in the

centre is composed of florets of a

very different type The pistil,as

in the ray-florets

,has an inferior

ovary of two carpels there is nocalyx ; the corolla is long and

tubular,with five teeth above .

Each floret has five stamens , the

anthers of which are united to form

a tube round the style SIIch

F 1 G . 1 2 2 . FLORE TS OFunited anthers are said to be

DAISY .— I

,ligu late , fe . syngenesious These are known

male ray—floret ; 2 , tubu as di sk—florets .

1 3 1 3 h ermaph mdi te d i $k‘ If the disk—florets in the head of

floret 3 , stamens Wi thunited anth ers ; 0 0 , in

a DaIsy are exammed,It WIll be

ferior ovary ; P,corona ,

seen that the outer (lower) floretsare the older, and are the first to

open . The following stages should be looked for : (1 ) thestyle is Short and within the anther- tube (when ripe the

anthers shed their pollen into the tube and on the topof the stigma

,wh ich

,has two lobes

,the outer face of

each being provi ded with a br ush of hairs) (2 ) later, thestyle elongates , and the stigmat ic brush sweeps the pollen


out of the tube ; (3) the stigma- lobes then open , throw

ing the pollen off , and exposing thei r inner surfaces for

pollination .

As the disk-florets open successively from outside inwards ,two stages will be seen : ( 1 ) the old florets with stigmas

exposed , (2 ) younger florets with pollen only exposed .

A single insect-visit may thus readily convey pollen from

one floret to the stigma Of another floret . Thus crosspollination of two degrees is possible : ( 1 ) a cross betweentwo florets of the same head , and (2 ) a cross between floretson different Dai sies . Honey

,which is secreted by a ring

like nectary round the baseof the style, rises in the tube in

such quantity as to be accessible to short-tongued insects .Thus the Daisy has gained many distinct advantages ( 1 )conspicuousness , due to aggregation of many small flowers

(2 ) a large supply of honey protected from rain by narrowtubes ; (3) accessibility of pollen and honey to a great

variety of insect vi sitors ; (4) pollen presented so as tosecure cross-pollination in the case of insect-visits , or selfpolli nation in thei r absence.

The Coltsfoot — The bri ght yellow flower-heads of theColtsfoot may be found in January or February

,when

insects are rare . The flowers appear before the leaves,and

from a single plant many flowering shoots of different ages

arise whi ch prolong the flowering-period . Growth is main

tained at the expense of food stored in its thick and often

long, underground stem, on which are the young leaves .Each flowering shoot is covered by smal l , very hairybracts

,and bears above a single capitulum . The bracts

of the involucre are in a single row and protect the florets

in the bud . Cut a capitulum vertically in two and note theflat disk ; determine the di fferent kinds of florets in thehead , and the interesting division of labour they Show

(Fig .

The outer, strap- shaped florets are the most numerous

M 2


(abou t three hundred) . Each has an inferior ovary, and

above i t is the calyx , consisting of a whorl of hairs . Such

a calyx is said to be pappose . Within this is the ligulatecorolla . The style has a two—lobed stigma

,and also

'

a brushof hairs , which , however, is of no use, as these florets haveno stamens , i . e . they are all pistillate no honey is secreted ,and they are ripe before the inner florets . About fortytubular flowers will be found in the centre, differingfrom the outer ones as follows : they are smaller and

less attractive ; the corolla is tubular and five- toothed

FIG . 1 2 3 . FLORETS OF COLTSFOOT .—I , ligu late, female ray

-floret ;

2 , tubular, male d isk-floret P a , pappus ; ao, ovary .

at the base , honey is secreted ; the ovule in the ovaryi s abortive ; there are five stamens with j oined anthers ,and the style has a pollen-brush , but not a functionalstigma . As the outer female florets are ripe before the inner

male ones , self-pollination cannot take place ; they are

therefore dependent on insect-visits . The chances of poll imat ion are increased by the prolonged flowering-period .

The Dandelion — Compare the flower-head of the Dandel ion (Fig . 1 0 4) with those of the Daisy and Coltsfoot , and

notice that the hollow stalk is devoid of leaves . 1 The

1 All parts of th e plant contain a milky ju ice or latex,a fluid

wh ich consists partly of waste substances , and to some extent ofnutriti ve materials . Th e latex is contained in irregu lar channelsknown as laticiferous vessels .


The Dandelion is visited by a great variety of insectswhich are able to obtain both pollen and honey very readily .

Its flowering-peri od is a long one, but i f the flowers are

out too early or too late for insect-visits self-pollinationis possible .

Flowers of the Potato and the Woody Nightshade or

FIG . 1 2 5 . I , WOODY NI GHTS HADE 2 , vertical sectionOf flower ; 3 , stamen ; P

,pore .

B ittersweet agree with Composite flowers in one respect,

viz . the anthers are j oined to form a tube (syngenesious) .The W oody Nightshade (Fig . 1 25 ) is frequent in hedgerows and is a lax climber . The flowers (Fig . 1 25 , 2 ) aresmall and in irregularly-branched inflorescences calledpanicles . The calyx of each flower has five united sepals ;the corolla has five purple, united petals, upon which are


five stamens alternating with the corolla- lobes the large

anthers are joined into a tube round the style and form

a conspicuous yellow cone, above which proj ects the two

lobed stigma . When ripe the a nthers dehisce by pores

at their free ends (Fig . 1 25 ,

The pisti l is superior,

and

consists of two united carpelsplaced obliquely in the flower

(Fig . 1 73 ) the ovary is two

celled wi th many ovules onaxile placentas . The flower

secretes no honey, but is

visited by bees for pollen .

I rregular and speciali zedflowers . The Germander

Speedwel l (Fig . 1 26) is pol

linated mai nly by drone—flies ,and shows several interesting

modifications . The flower (2and 3) has four sepal s , thefifth posterior one being ah

sent . The blue corolla has

four petals,but the large

osterior one reall re resents

Ewo fused petalgI

All areF IG ' 1 26 ' I

’GERMAND

-

ER

S PEEDWELL ; 2 ,flower showmg

j oined into a. ShOI'

t Ulbe . th e position of the stamens and

There are only two stamens , style ; 3 . flower in vertical

and these spread out hori section ; a , stamens ; br , bracts ;l , opposi te decussate leaves

z ontal ly . The pIStl l consists raceme ; st, style .

of two united carpels,and the

style projects over the anterior petal . A fleshy disk belowthe ovary secretes honey

,which is protected from rain by

hairs on the corolla .

As the fly alights , i t first touches the s tigma,then grasps

the two stamens , pulling them to the S ides of its body,


FIG . 1 2 7 . FLOWE R OF V IOLE T .— 1

, solitary axi llary inflorescence2, a leaf ; 3 , flower in vertical section ; 4 , stamens and pistil5 , pisti l removed ; 6 , seed ; c , membraneous prolongation o f

anth er-connective ; f , flap Of stigma ; n, nectary ; s , spur ; s .P ,

stigmatic pit ; st, foliaceous stipu les .


Violas are horizontal (Fig . 1 29, while those of Pansies aredi rected upwards (Fig . 1 29, These differences may be

somewhat masked in cultivated forms wi th very large

petals . Irregular (zygomorph ic) flowers , as those of the

Violet , are well adapted to the structure and habits of bees .

They not only provide honey protected in tubes or spurs ,but are frequently scented

,and in the highest forms have

a blue colour .Sweet Violets grown in poor soil and in a shady place

often cease to develop the typ ical showy flowers , yet ripe

capsules full of seeds may be formed . Careful examination

will reveal a few very small inconspicuous flowers , resem

bling small flower-buds, at the base of the plant and overshadowed by the leaves . These

flowers never open they regu

larly fertilize themselves and

produce an abundance of ripe

seeds . Sometimes both kinds

of flowers occur on the sameF IG ' 1 29 ' plant . Simi lar closed flowers

1 , FLOWE R OF V IOLA .

2 ,FLOWER OF P ANSY '

occur In the Wood Sorrel and

Henbit Deadnettle (Lamiumamplexicaule) . Such flowers are called c leistogamous (Gr .kleistos closed) . Cold

,absence of sunshine ,

and a poorsoil , favour their development .Columbine

,M onkshood

,and Larkspur .

— The Columbine

(Fig . 1 30 ) is a humble-bee flower . Its sepals are coloured ;its five free petals are prolonged into large spurs whosecurved and fleshy ends secrete honey . The stamens areindefinite, but the inner ones do not produce pollen . Such

barren stamens are called staminodes . In the centre are

the five carpels slightly j oined at the base . The stigmas

ripen later than the stamens . The flower is pendulous,and

the bee, in order to obtai n the honey,has to cling to the

base of the spur and also to the column of stamens and


carpels . It thus becomes dusted with pollen , which itcarries to older flowers where the stigmas are ripe .

It requires an insect with a long proboscis to Obtain thehoney from s o long a tube . Often , however, the humble

FIG . 1 30 . 1 , V ERTICAL SE CTION OF FLOWE R OF COLUMB INE ; 2 ,

VERTICAL SE CTION OF FLOWE R OF MONKSHOOD 3 , S IDE V IEW OF

FLOWER OF LARKS P UR 4 , front V iew of th e flower ; 5 , flower invertical section ; n , nectary ; P

, petals ; s .P , honey-secreting spurof petal ; s .s, spurred sepal .

bees bore holes in the spurs and SO Obtain the honey without

effecting pollination . These holes may then be used by

other insects which do not themselves pierce flowers .

The Monkshood (Fig . 1 30 , 2 ) is another humble-bee


flower,and the plant grows wild (

only where humble-bees

are found . It has five blue sepals , the posterior one forminga large hood which protects the anthers and nectaries .

The two posterior petal s are modified to form long, clawednectaries or honey- leaves (n) and the other petals are

usually absent . The stamens are indefinite and they ripen

before the st igmas (i . e . they are proterandrous) .The Larkspur (Fig . 1 30 , 3 , 4 , 5 ) has five sepals and two

spurred petal s ; the posterior sepal is prolonged into a

membraneous spur which encloses the honeysecreting spurs

of the two posterior petal s . The flower of the Columbine

is regular, wh ile those of Monkshood and Larkspur are

irregular .Sweet-P ea

,S carlet-Runner , and Gorse.

— The Sweet-P ea

(Fig . 1 3 1 ) is a complex bee-flower . Its calyx has five

united sepals,two above and three below . Its corolla has

five petals curiously shaped and known by distinctive

names (Fig . 1 3 1 , The large posteri or petal is the

standard (s) , the two lateral ones are the alae or wings (a) ,and the two anterior ones

,which are slightly j oined , form

together the carina or keel (k) . Note carefully how theseare related to one another, especially at the base, observing

that depressions in the wings correspond to bulges in the

keel . Enclosed in the keel are ten stamens,nine of them

being united by their filaments to form a stamen- trough

around the pistil,the posterior one lying free over the slit

(Fig . 1 3 1 ,When the stamens are united by thei r

filaments into two sets they are said to be diadelphous .

The filaments and s tyle are bent upwards at the end of thekeel . Honey is secreted by the bases of the stamens

,and

collects in and is protected by the stamen- t rough

A clever insect l ike the bee is required to open the flower

and obtai n the honey . It uses the wing-petal s as an

alighting stage but these being articulated wi th the keel ,both are depressed by the weight of its body . When the


bee pushes its proboscis into the tube, it obtains the honeythrough two openings

,one on either side of the base of the

free stamen . The stamens and style are thus exposed

the pollen is swept out by a brush of hai rs at the end of the

style and dusts the under surface of the bee . When the beefli es away, the keel springs back to its former place . If atthis time the stigma is ripe, it may be touched wi th pollen

as the keel returns to i ts place ; Self-pollination would thus

occur . AS the bee fli es from flower to flower it may deposit

pollen on the stigma of another flower of the same species

and s o effect cross-pollination .

The pistil (Fig. 1 3 1 , 3) consists of one carpel (apocarpous) ,and is covered with hai rs . Look for the small ovuleswi thin the ovary .

Other pea- like flowers should be compared with the

Sweet-Pea ,and thei r characterist ics noted . The Vetch ,

Broad Bean , and Scarlet-Runner are similar to the Sweet

Pea : the style is provided with a pollen-brush and the

flowers may be visited a number of t imes . The Scarlet

Runner,however, is peculiar in that the keel and style are

spirally coiled . The flower of the Garden Pea is regularlyself-polli nated . NO European insect is strong enough toopen the flower and pollinate it . The White Clover produces much honey, and its short flower-tube does not

exclude short- tongued bees . When an insect alights on

the wing-petals,the stamens and stigma emerge from the

flower . After the visit they return to thei r former positionwithin the keel .The Gorse (Fig . 1 32) differs in several respects from the

above . All the stamens are united to form a tube ; no

honey is secreted, and the flowers are vi s ited by bees andother insects for the sake of the pollen . The stamens ripen

and shed their pollen into the tip of the keel . A bee, resting

on the wings and pressing its head beneath the standard ,

bursts open the keel and the unde r side of its body is first


touched by the stigma and then receives a shower of pollen .

The wings and keel are dislocated ; they hang vertically

downwards,and cannot return to thei r former position .

If the bee is dusted with pollen from another flower, crosspollination will occur i f not

,self-pollination may take

place as the insect leaves the flower . Imitate the action of

the bee by depressing the keel wi th a pencil and watch the

FIG . 1 32 . GORSE .—l, leaf s , spine .

explosion . Such explosive flowers can profit only by one

visi t .Summary of thevarious grades offlower structure — Flowers

may be regarded from two points of V iew the

Biological , which is concerned wi th the functions of theflower and its relations to the outs ide world

,especially wind

and insects . In the series of flowers which we have studied ,

we find an increase in complexity of structure from simplewind-pollinated flowers to more complex insect—pollinatedflowers , and i n the latter, commencing wi th flowers in the

form of an open cup,and accessible to the lower orders of

insects , we find a tendency to form a deeper flower-tube,


a union of sepal s and petals , production of honey and scent ,and at the end of the series we arrive at special forms with

irreg ular flowers . These are so constructed as to excludethe lower forms of insects

,but are attractive to and visited

by the higher and more intelligent forms , e . g . bees,moths

,

and butterflies .Colour-changes follow somewhat similar lines of develop

ment . The S impler flowers are small,green

,and moon

spicuous , a stage higher the petals are larger and yellow or

white,while the tubular and more complex flowers are

often red,blue,

or V iolet .

(2) The Morphologi cal point of view, which regards the

structural differences , forms , and relationships , of the parts of

the flower . If we summarize the chief structural differences

we find that the small and simple flowers of the P oplar andWillow have no calyx or corolla . Thei r flowers are unisexual and arranged in catkins , the male and female catkins

occurring on different trees,i . e . they are dioecious . In the

Oak and Hazel both male and female catkins occur on thesame tree

,i . e . they aremonoecious . The Anemone, Butter

cup ,Marsh Marigold

, Columbine,Monkshood , and Larkspur

are hermaphrodi te,and though differing much in form and

colour,all agree in possessing a free calyx and corolla

,

numerous hyp ogynous stamens , and a superior apocarpouspistil . The perianth is whorled or cyclic , but the stamens

and carpels are arranged spirally on the axis . The Stock

agrees with the above in that the sepals and petals are free,

but there are only s ix stamens,four long and two Short .

The ovary consists of two united carpels , divided by

a central plate . All the whorls are cyclic . The Violet ,while having free sepals and petals has an i rregular corolla

,

one petal being spurred . The pistil consists of three unitedcarpels and a one-celled ovary .

Important differences from the above are met with in


stem are arranged in a ring ; the leaves are net—veined

and the parts of the flower are usually disposed in fours orfives . Further, the seeds have two cotyledons , and they

therefore all belong to the same great class of flOweringplants called D icotyledons .

We now proceed to a few examples belongi ng to th e

other great class , the Monocotyledons .

CHAPTER XIV

BIOLOGY OF THE FLOWER (Continued)

MONOCOTYLEDONS

Hypogynous flowers , wi th three parts in each whorl .

Another type of flower , constructed on a different plan

from the preceding, is represented by plants such as the

Bluebell and the Daffodil . The flowers of the Bluebel larise on the upper part of a long leafless axis or scape

(Fig . 1 33 ,Each flower (Fig . 1 33 , 2 ) is attached by

a stalk or pedicel , at the bas e of which are two long,narrow ,

coloured bracts which cover the young flowers when in

bud (br) . An inflorescence of this kind with stalkedflowers , of which the Oldest is at the bottom and the othersare in success ion younger as we near the top ,

is called a

raceme .

The parts of the flowers are arranged very regularly inthrees (trimerous) . On the outside are three sepals , thenthree petals , and the s ix are slightly j oined together at

the base . Here the sepals and petals are all similar andcoloured

,and the name per ianth may be used to indicate

the two whorls when they are not differentiated into calyx

and corolla . There are S ix stamens,three outer and three

inner,fixed below the pistil

,which is in the centre and


consists of three united carpels . The ovary is superior and

divided into th ree chambers , and above i t is a long style,terminating in a three- lobed stigma . Cut the ovary across ,and note that the ovules in each chamber are attached to

the axis in double rows , i .e . the placentation is axile . Honey

is secreted by glands in the ovary-wall between the carpels ,

and is much sought for by bees . The three outer stamens

ripen before the stigma,and the anthers (at first vertical)

F IG I 33 WILD HYAC INTH FIG . 1 34 . VERTICAL SECTION OF

— 1» 1 3 0 9 1 1 1 0 5 9 Inflorescence ; DAFFODIL FLOWER .

— oo, corona ;2, verti cal section of flower 0 9 , ovary ; 3p, spathe .

br , bract ov, ovary ; P o,

ped icel ; s , scape .

dehisce inwards (introrse dehiscence) , then turn horizontallyand almost close the entrance to the flower . A bee visiting

the flower presses its head into the corolla,forces apart the

deeply-divided lobes,and in doing so becomes dusted with

pollen . The style now elongates,the stigmas ripen and

may become cross -pollinated . At this time the three inner

stamens dehisce,and i f cross -pollination does not occur ,

self- pollination is certain , as the three stigma- lobes whenripe come into contact with the anthers .

Ep igynous trimerous flowers — The Daffodil has three

N 2


outer and three inner perianthleaves united into a tube ,

an outgrowth from which forms a large bell-shaped corona

(Fig . 1 34 , co) . Interesting modifications of this may be seen

in different species of Narcissus in some the corona is in

the form of a small , brightly- coloured ring,and gradat ions

may be found from this up to the large corona of the

Daffodil . The S ix stamens , in two whorls of three,are

attached to the perianth . The pistil , however, differs from

that of the Bluebell , in that the ovary is inferior . The style

is long,reaching to the mouth of the tube, and has three

stigma-lobes . The pistil consists of th ree carpels and the

ovary is three- celled, with axile placentation . The bractof the Daffodil is in the form of a drymembraneous sheathor spathe (sp) .Examine flowering specimens of the Crocus , and note

,

when closed flowers are brought into a warm room,how

quickly they open , the lobes Often becoming strongly

reflexed . The flowers and leaves are surrounded by

colourless sheaths , which keep together and protect the

inner parts while they are growing through the soil . Re

move the sheaths,and note how limp and S lender are the

organs within , and how dependent they are upon the

support of the sheathing cylinders . An interesting example

of division of labour is thus afforded . Note the scale- leaf

in the axil of which this flowering shoot arises , and observe

that the base is already enlarging . Thus we see a youngcorm forming as a branch upon the old one (Fig .

Remove the foliageleaves and note thei r mode of attach

ment (see p . 1 33 and Fig . The flower is surrounded by a

thin,colourless sheath (Fig . 1 35 , sh) , and is supported on an

under ground cylindrical stalk— the scape (so) . The perianthleaves are in two whorls of three each ,

and are united to form

a narrow tube three to four inches long . There are three

stamens fixed to the top of the tube the large arrowhead

shaped anthers (a) dehisce outwards (extrorse dehiscence) ,


tongues (such as the hawk-moths) are able to extract the

whole of it . Insects vi siting the flower for honey will at

first become dusted with pollen, which may be transferredto an older flower with ripe stigmas . If insects fail , the

stigma—lobes curl outwards between the anthers and become

self-pollinated— an advantage in a species flowering early

before many insects are about . As the fruit develops , the

scape elongates and carries the ripening capsule above

ground , where it dehisces and the seeds are scattered .

The flower of the Ir is (Fig . 1 36) has three large outerand three small inner perianthleaves , but has only three

stamens,the inner whorl being suppressed, and , as in the

Daffodil , they are above the ovary, i . e . they are epigynous .

The three styles are transformed into large petal oid lobes ,against which lie the stamens . On the under side of these

lobes and near the tip is a little flap covering the s tigmatic

surface . As in the Daffodi l , the flowers are enclosed ina large spathe . The petal oid style arms (sy ) of the Iris areOften applied to the perianthleaves in such away as to form

a split tube , at the base of wh ich are honey-glands . The

difference in S ize of the perianthleaves,together with the

large petaloid styles , gives to the Iris a striking, and at firstrather

‘

puz z ling , appearance .

TheOrchidflower — Still more puzzling is the flower of thePurple Orchis (Fig . Each flower arises in the axilof a bract and appears to be s talked , but the stalk consistsof the inferior ovary and is twisted (2 , ov) . Hence the flowers

are sessi le and the Oldest are below as in a raceme .

Such an inflorescence of sessile flowers is called a spike .

The perianth is epigynous , consisting of six perianth

leaves , one of which (the labellum) forms an alighting

stage (Fig . 1 37 ,l) , while the others form a hood , covering

in the stamens and stigmas . From the base of the labellum

is produced a tube or spur in which honey is secreted .

There is only one stamen (a) , the remainder being sup


pressed . Two of them,however, are represented by small

,

barren stumps , called stam inodes (st) , one on either side of

the stamen . Just below the single stamen , which lies under

the hood , is a sticky disk— the rostellum (r )— and on either

s ide of it is a stigmatic surface .

Imitate the action of a bee by inserting the point of

a pencil into the th roat of the flower, and in doing so pressit against the rostellum . Now remove it , and if the stamen

FIG . 1 37 . P URPLE ORCHIS .— 1

, front view of flower ; 2, side

V iew o f floWer 3 ,pollinium ; 4 , anther and stigma- lobes 5 ,

pollimum removed from a flower and bend ing horizontally ; a ,

anth er ; l, labellum ov, ovary ; P , pollinia ; r , rostellums , stigma sp, spur ; st, staminodes .

is ripe , notice that two stalked , club- shapedmasses of pollenadhere to the pencil (Fig . 1 37 , These are called pollin ia (P ) , and are the masses of pollen from the anther

lobes . Watch them for a moment and note that they bendinto a hori z ontal pos i tion

,turn outwards a little; and are

therefore suitably placed for coming into contact with the

stigmatic surfaces when again inserted into a flower . Tryto brush the pollinia off the pencil and you will find thatthe secretion glues them so firmly to the penci l that some

force is required to remove them .


The Orchid illustrates great modification in a mono

cotyledonous flower. The perianth is i rregular (zygomor

phic) the posterior petal of the inner whorl projects as

a lip or labellum,and serves as an alight ing stage for insects .

Below,it is prolonged into a honey—secreting spur . The

other petals form a hood , protecting the pollen and honey.

The essential organs are borne on a prolonged outgrowth of

the axis , called the column,on the top of which are one

fertile and two barren stamens , and two stigmas , also the

rudiment of a third stigma— the rostellum (r) —o n whichare developed the two sticky bodies which glue the pollinia

to the bee’s head . The ovary (ov) is inferior, stalk- like, and

twisted. When ripe, the frui t contains a large number ofminute seeds .

Reference to the floral di agram (Fig . 1 79) will help tomake

the various relationships clear . S ix stamens,in two whorls of

three each , ought to be present , but of the outer whorl onlythe anterior one is present , and it is over the rostellum.

The other two a.re suppressed , and their position is

represented in the diagram by a cross x . Of the inner

whorl , the posterior stamen is suppressed , and the twolateral ones are reduced to short , barren s tumps calledstaminodes . The anterior s tigma is transformed into

the rostellum the two lateral ones are functional‘

and lie

below the stamen , one on either side of it . As the flowerdevelops , the s talk- like inferior ovary twists throughand carries all the parts of the flower round , so that the

posterior lip comes to be anterior in the open flower . The

diagram (Fig . 1 79) represents the parts before twistingoccurs .F lowers of Grasses .

— The flowers of Grasses are small,and the parts can be made out only by careful observation .

The inflorescence is usually ei ther a compound spike or

a panicle and what appears to be a single flower is a groupof sessile flowers , or spikelets (Fig . 1 38, A dissected


flower-stalk is a fourth scale, the inner pale ; then follow

two minute scales called lodicules (l) , immediately abovewhich are three stamens with long

,slender filaments and

large, easily moved (versatile) anthers . At the end of the

flower—axis is the pistil,consisting of one carpel . The ovary

contains one ovule and above i t are two large, feathery

stigmas . There is no perianth unless the two lodi culesmay be so regarded , but this is doubtful , and the flower is '

said to be naked . Sometimes there are two pairs of pales,and the lower ones may bear bristles , or awns , as in the

Vernal -grass (Fig . 1 38, in which flower there are no lodi

cul es and only two stamens . In most cases the stamensripen and shed thei r pollen before the stigmas are ripe , but

in the Vernal-grass the stigmas are ripe first . The long,slender filaments and large

,easily moved anthers , the great

amount of pollen and the big, branched , feathery s tigmas ,are excellent devices for wind-pollinat ion while the fact

that the anthers and stigmas of the same flower are notripe at the same time secures cross - fertilization .

To summarize : The flowers of Monocotyledons Showa series of modifications

,from simple types pollinated by

the wind to complex forms adapted to the habits of special

insects . The Grasses,l ike the Willows , have no perianth ,

and the essential organs are enclosed by bracts calledglumes and pal es . The three stamens with thei r slenderfil aments and large versatile anthers , and the branchedstigmas , are adapted to wind-pollination . The ovary is

superior and contains one ovule . The flower of the Blue

bell is cyclic , and the parts are in five whorls of three eachthe perianth is petaloid the syncarpous ovary is superior ,three- celled, and contains many ovules . The Daffodi l

differs from the Bluebell in that its ovary is inferior and the

perianth has a corona . The Crocus also has an inferior

ovary, but has only three stamens . The flower has a long

tube, and the stigma- lobes are large . The flowers are


attractive in colour and secrete honey, but , failing insect

visits,self pollination commonly occurs , an advantage in

early flowering species In the Iris the stamens are peta

loid and large enough to be conspicuous . The greatestspecialization occurs in the Orchids

,which have i rregular

flowers , long honey-secreting spurs , stamens reduced to one,

rarely two ,and united to the style (gynandrous) . They

are usual ly incapable of self—pollination . The capsules

produce an immense number of minute seeds .

CHAPTER XV

POLLINATION, FERTILIZ ATION, AND THE

ORIGIN OF SEEDS

FROM our study of flowers we learn that all the partsof which they are composed serve directly or indirectly to

secure the production of seeds . The modifications are very

numerous , but in most cases they a re definitely relatedto pollination , which precedes fertilization . Except in rarecases, ovulesmust be fertilized before seeds can be developed .

Advantages of self and cross-pollination.

—The flowers of

most plants are developed in air, and the pollen -grains

have to be carried through air from the anther to the stigma .

The chief mean s by which th is i s secured may be sum

mari z ed as follows1 . Self-pollination , where the pollen falls on to the stigma

of the same flower . This occurs in flowers which neveropen , like some of the Violets and Wood Sorrel , also in

certain species of Deadnettle and Vetch . These -are knownas c leistogamic flowers (see p . S elf-pollination isvery common in flowers where the pollen and stigma are

ripe at the same t ime, e . g . in the Buttercup , Dwarf Mallow,


Scarlet P impernel , S tock ,and Crocus . It is an effect ive

means of securing a crop of seeds if cross—pollination fail s .2 . Cross-poll ination , where the pollen is carried to the

stigma of another flower on the same plant or to the stigma

of a flower on another plant of the same Species .Devices which favour or necessitate cross-pollination are

very common , and seeds resul ting from such a cross areOften more numerous and produce better and healthierplants than when self—pollination occurs .

The more important means of securing cross-pollinationare

1 . S tamens and pistil occurring in di fferent flowers (diclinous : Gr . di double

,kline a bed ) .

(a) Staminate and pistillate flowers on the same plant

(monoecious) , e . g . P ine, Hazel , Oak , and Birch .

(b) S taminate and pistillate flowers on separate plants

(dioecious) , e . g . Willow,P oplar , Red Campion , Dog

’sMercury , Crowberry .

2 . Stamens and pistil occurring in the same flower

(hermaphrodite) , but are not ripe at the same time (dicho

gamous : Gr . di cha in two parts) , though the male and

female stages usually overlap, at which t ime self-pollinationmay occur .

(a) S tamens ripen and shed their pollen before the pistil

is ripe (proterandrous) , e . g . Daisy , Dandelion , and otherComposi tae ; Mallow

,Wood Sorrel , Meadow Crane’s-bill ,

Chervil and other umbelli ferous flowers .

(b) P istils ripen before the stamens (proterogynous) ,e . g . Field Wood- rush and P lantains .

3 . Anthers and stigmas are so S i tuated that the pollen

does not fall on to the stigma, e . g . Pansy, Buttercup (see

pp . 1 67—8)

4 . D i fferent forms of flowers occur in the same Species

(heteromorphic , Gr. hetero di fferent) .

(a) Long and short-styled forms (dimorphic) , e . g .

2 0 6 THE REPRODUCTIVE ORGANS

and some, often scarlet exotic flowers , are pollinated byhumming-birds .P ositions of honey -

glands .

— Nectaries occur, as we have

seen , on many different organs , but usually they are on

some part of the flower

(a) On the receptacle at the bases of the short stamensin the Wallflower and Stock

(b) On the sepals of the Mallow and Coronilla

(c) On the petals of the Buttercup and Lesser Celandine,and in the spurred petal of Orchis

(d) On the stamens of the Violet and Pansy , the Spuracting as a honey-receptacle

(e) On the carpels of the Marsh Marigold and Bluebell .Nectaries sometimes occur on leaves (extra-floral nec

taries) (Fig. 2 1 9, p . These attract numerous ants,

which in turn keep off the caterpillars that would eat the

leaves .

Fertiliz ation and the Orig in of Seeds

S tructure of the p isti l . —The pistil is the inner essential

organ of the flower . In a typical and S imple case like thatof the Pea i t may be regarded as an up- rolled leaf (Fig .

bearing on i tsmargins smal l rounded bodies cal led ovulesIf we suppose the turned-in edges to meet and fuse, soenclosing the ovules in a box, we can form some idea of its

structure. The ovule-bearing portion is called the ovary (co) ,and that part of the edge from which the ovules spring iscalled the placenta (pl) . Its tip is prolonged and known

as the style, and at the end of i t is a portion which receives

the pollen , called the stigma . Such an ovule-bearing leaf

is called a carpel , and in the case of the Pea the pistil con

sists of one carpel only .

In the S tock the pistil i s composed of two united carpelsin the Clematis

,Buttercup

,Marsh Marigold, and Rose , i t

FERTILIZ ATION AND THE ORIGIN OF SEEDS 20 7

consists of man y free carpels . When the pistil consists

of one or more free carpels i t is said to be apocarpous ;and when of two or more carpels united together, i t is syncarpous . If i t arises above the other parts (calyx , corolla ,

and stamens) i t is superior, and i f bel ow,i t is inferior .

Sometimes botanists use the word pistil in a differentsense . When the carpels are free each con

‘

sists typical lyof an ovary

,style, and stigma . Then

the flower is said to have manypistils

,e . g . the Buttercup but

when the carpels are j oined, as in

the Stock and Tulip , the flower i ssaid to have only one pistil . The

name gynoec ium i s given to the

central part of the flower, whether

consisting of one carpel or many,

free or j oined .

The ovule and the embryo-sac.

When the ovule first appears on

the placenta i t consists of a smal l

outgrowth of tissue, the nucellus

(Fig . 1 40 , n) . Around the base of this , F IG . 1 39 . D IAGRAMtwo coats grow upwards and cover OF OP ENED P IS TIL .

the nucellus , with the exception of funid e ? 0 , “1 1 1 3 ?

ovary ; P l , placenta ;a minute pore

, t ch remains at theP 0 , p 0 1 1m g rains ; P .t,

end and forms themicropyle . Wi th In po llen-tube ; S , stigma

the nucellus a large cell arises , called sr . style .

the embryo -sac (em) , within whichseveral cells are formed , one of these, near the micropyle ,

being called the egg-cell .Fig. 1 40 ,

1 —3 , illustrates these points . In these the ovulei s represented as a straight one, but this form is not common .

More usually the ovule during its development becomes

bent and often inverted , so that the micropyle i s broughtdown to the base of the ovule stalk or funicle . Such an


inverted ovule is sai d to be anatropous (Fig . 1 4 1 ,2 ) (Gr .

ana,denoting inversion ,

trepo I turn) . A straight one

is orthotropous ( 1 ) (Gr . orthos straight )‘ when curved

it is campy lotropous (3) (Gr . kampy los curved) ; and

when at right angles to the funicle, amphitropous (4)(Gr . amphi on both sides) .

FIG . 1 4 0 . DEVELOPMENT OF AN OVULE .

— em, embryo -sac

n , nucellus P, outer integument s , inner integument .

FIG . 1 4 1 . FORMS OF OvULE s .— I

, orthotropous 2, anatropous

3 , campylotropou s 4 ,amph itropous em,

embryo -sac f , funicle ;n , nucellus p, Outer coat or primine s , inner coat or secund ine .

When the ovule has developed thus far i t is ready for

fertilization . Before this can take place, however , pollen

grains of the same Species must be deposited on the stigma .

This , when ripe, is covered with a sticky,sugary secretion ,

in which the pollen - grains germinate .

Germination of pollen-

grains , andferti li zation .

—By means

of a simple experiment a good idea may be Obtained of

what occurs . P lace a drop of 1 0 per cent . solution of canesugar on a glass slip and put into the solution a few pollengrains of the Sweet -Pea . If examined after an hour or two ,

short,delicate tubes called pollen- tubes will be seen emerg


The differences between ovule and seed are importantand may be stated as follows

OVULE SEED .

B ef ore ferti li z ation .

2 ovu le -coats S eed -coatNu cellus $Nu cellus and

Embryo -sac endosperm Used

up as food for]Egg

-cell Embryo

Sometimes only part of the endosperm is used up ; the

embryo then is relatively small and more or less endosperm

persists round the embryo in the seed . Examples of thisoccur inWh eat , Maize, Common Ash , and Castor Oil . Occasionally some of th e nucellus persists , when it is cal ledperi sperm .

Thus foodreserve may be stored in various regions ina seed : in the cotyledons of the embryo (Bean) , in theendosperm of the embryo - sac (Wheat , Ash) , and in the

perisperm or persistent nucellus (Water- lily ,Pepper)

The ovule is not the only part affected by fertilization ;many surrounding parts are affected alsoIn the Pea ,

the carpel grows enormously and forms the

pod . In the Stock ,the two carpels elongate greatly. In

the S trawberry,Rose

,Apple, and P ear , the receptacle

becomes not only very large but fleshy . In the WinterCherry (P hy salis) , the calyx becomes much inflated and

brightly coloured . In the Fig, Mulberry,and P ine- apple ,

the whole inflorescence or parts of i t become fleshy, fuse

together , and form a very complex aggregate fruit .The changes that take place as a result of fert ilization

are,therefore

,very great . The union Of the two elements ,

a nucleus from the pollen -

grain and the nucleus of the egg

cell , results in a stimulus to growth which is the startingpoint in the life -history of a new plant . The growth

stimulus produces the changes we have outlined both

Af ter ferti li z ati on .

2 ovu le -coatsNucellus

Embryo -sac

EndospermYoung embryo

FERTILIZ ATION AND THE ORIGIN OF SEEDS 2 1 1

within the ovule and in adj acent parts , and carries them on

till the seed is ripe and ready for an independent existence .

But some of the changes may go on ,and fruits form even

in the absence of fertilization, as in fruits like the Banana,

seedless forms of Orange, Grape , and others . These, how

ever, do not contain ripe seed capable of germination .

CHAPTER XVI

STRUCTURE OF FRUITS

THE fruit is the structure produced from the pistil asa result of fertil ization . In the Pea and Bean ,

this consists of one carpel , but in the Stock there are two united

carpels . Commonly, however, the pistil consists of several

carpels , sometimes free as in the Buttercup , sometimesunited as in the Violet and Crocus .In common edible fruits the fleshy part which is eaten ,

Often consists of structures other than the pistil . Theseare known as false fruits , while those formed from the

pistil only are known as true fruits .

In al l cases the object of their formation is the production of seeds , containing a young plantlet capable of growinginto a new plant . In some fru its the fruit-coat or pericarpis dry and does not split until the seed within germinatesin others , the frui t - coat splits and the seeds are scattered .

Others , again , have a succulent or fleshy fru i t -coat,and

most of our edi ble fruits belong to this class . A few specimens of each kind should be obtained and carefully studied .

Dry indehiscent frui ts — The Hazel-nut (Fig . 1 87 , 8 )is enclosed in a cup consisting of large ,

leafy bracts .Break open the hard , dry shell and note the S ingle seedwithin (somet imes two may be found) . Look for the

o 2


seed-stalk and notice how i t is attached . The seed-coat i sthin and brown and surrounds an embryo consisting , as

in the Bean , of two fleshy cotyledons,a radicle, and a

plumule .

Compare with this the Acorn (Fi g . Here the

bracts are numerous , small , and form a compact cup . The

smooth fru i t-coat encloses one seed , the embryo has twolarge fleshy cotyledons . Such hard

,dry

, one—seeded fruits

FIG . 1 4 3 . FRUIT OF OAK .

— I,Acorn with cupu le ; 2

,vertical

section of same c,cotyledon cu ,

cupule ; f , remains o f flowerp ,p lumule P e, pericarp r

,rad ic le t, testa .

are called nuts . The Sweet Chestnut and the Beech are

other examples .

The fru i t of the Buttercup (Fig . 1 44) consists of manysmall , dry ,

one-seeded fruits , each the product of a separate

carpel , and attached to a somewhat swollen receptacle .

Each one is called a nutlet or achene .

The Strawberry (Fig . 1 45 ) is very similar , but the

receptacle is Slightly hollowed ,and from i ts centre grows

a large ,fleshy structure , in which the achenes are embedded .

The Rose-h ip (Fig . 1 46) differs from the above in that the


receptacle is hollowed and bears the achenes on the innersurface of the cup . Both in this and in the Strawberry

the fleshy part is the receptacle ,and these frui ts are there

fore succulent frui ts containing many dry indehiscent

nutlets .

Fruits like those of the Dandelion (Fig . Col tsfoot ,Thistles , &c . , are achenes ; but they are formed from an

inferior ovary of two carpels , only one of which matures ,and that contains but one seed .

FIG . 1 48 . I , CREMOCARP OF HOGWEED ; 2,mericarps separated ;

c, carpophore ; m, mericarp ov, ovary ; st, stigmas .

The fruits of Grasses like Wheat , Maize,and Oat differ,

as we have seen , in that the fruit-coat and seed-coat closelyadhere .

The Sycamore key (Fig . 20 2 , 5) consists of two or morecarpels , which ,

when ripe,separate

,

into part- fruits (mericarps) but do not scatter the seeds . Each part containsone seed

,and i s provided with a wing . Cut open a frui t

observe the thick fru i t -coat l ined with a fel t of hairs and the

seed within covered by a thin brown testa . Remove thisand examine the embryo carefully see how the cotyledonsare rolled up . Make a paper model to Show clearly how

they are folded and rolled (Fig . 20 2 , Such winged fruits

STRUCTURE OF FRUITS 2 1 5

are called samaras . Other examples are the Maple,Ash

,

Elm, and Birch .

Another common type which spli ts into two hal f—frui tsis found in the Hogweed , Chervi l , and other umbelliferous

plants . A ripe frui t of the Hogweed (Fig . 1 48) is easy todi ssect . I t consists of two flattened carpels

,which readily

separate into two half- fruits (mericarps) , and remainingattached by a slender stalk , the carpophore (c) , each

FIG . 1 5 0 . 1 , S ILIQUA OF SHEPHE RD ’

S P URSE ; 2, siliqua de~

h isc ing ; r , replum with seeds

attached .

FIG . 1 49 .

FOLLICLE S OF COLUMB INE .

mericarp containing one seed . Such fruits are called

cremocarps . Caraway seeds are hal f- fruits of this kind .

Dry dehiscentfruits — In all the above, when the frui t is

dispersed , the thick protective coat does not burst until

germination begins , such seeds usually having only a thin

testa . Dry fruits of a second Class have a fruit- coat which

splits , and so al lows the seeds to escape. These, not havingthe protection of the fru i t - coat

,are usual ly surrounded by

a thick testa . They include many common frui ts , and

several should be examined , and the different modes of

splitting (or dehiscence) compared .

The Columbine (Fig . Monkshood , and Marsh


Marigold have a pistil of several free carpels . Each ispod- like and contains many seeds ; but , unl ike a pod ,

Spl its along the inner seam only . These fruits are called

follicles . The legume or pod of the Pea and theh

Bean

consists of one carpel and spl its along both seams , the twovalves often being twisted into a close spiral (Fig . 1 62 ,

The Shepherd’

s Purse (Fig . 1 50 ) and Honesty are simi

lar to the S tock , but shorter , and their pods are known as

FIG . 1 5 1 . 1 , OPEN CAP SULE OF V IOLE T ; 2, CAP SULE OF P OP PY

DEHI S C ING B Y P oRE s ; 3 ,SAME IN SE CTION ; 4 , CAP SULE OF P IM

P ERNEL DEHIS C ING TRANSV ERS ELY ; P, pore ; s , edges of carpels

whi ch proj ect into the ovary but do not meet in the centre .

siliquas . Compare these and note how very di fferent forms

of frui t may arise from one type of structure .

A common type of dry splitting fru i t which is more or

less globu lar is called a capsule ,and dehiscence takes place

in a variety of ways . Some capsules open above, forming

a cup surrounded by teeth ,as in the Campion (Fig . 1 59,

In the V i olet (Fig . 1 5 1 ,1 ) i t opens by three valves . Other

capsules dehisce by pores , as in the P oppy (Fig . 1 5 1 , 2 and

where the pores are around the margin and in the Snap

dragon the capsule is oblique and has three pores (F ig . 1 59,

In some Campanulas the pores are at the base (Fig . 1 59, 5 )while in the globular frui ts of the P impernel (Fig . 1 5 1 ,


The Gooseberry (Fig . Grape,Currant

,and Tomato

are syncarpous frui ts , in which the endocarp i s succulent aswell as the mesocarp , and they have one cavity (loculus )which contains several seeds . Such fruits are known as

berr ies . The name berry is also given to many common

FIG . 1 54 . FRUIT OF GOOSE

BERRY .— 1 , berry in vertical

section ; 2 , in transverse sec

tion ; c, remains of flower ; e,

epicarp m mesocarp 3 , seeds

embedded In succu lent endocarp .

fruits l ike the long fruits of Gourd , Cucumber , and Banana .

The latter is without seeds , the plants being propagated

from rhizomes .The Date is one- seeded , the seed being hard and stony .

The Orange and Lemon have a leathery epicarp , and are

divided into several chambers . In berries l ike the Currantand Gooseberry the fruit is inferior , the calyx being on the

top of the frui t ; while the Tomato,Grape, Orange, and

FIG . 1 5 5 . P OME OF AP PLE .

1, transverse section, show

ing the five carpels ; 2,ver

tical section ; 0 , remains of

flower ; e, epicarp ; en ,endo

carp or core ; m,mesocarp ;

s , seed .

STRUCTURE OF FRUITS 2 1 9

Lemon are superior . The Pomegranate is peculiar in thatthe edi ble part consists of the succulent testas of the seeds .The Apple and the Pear , as is the case with the Rose and

the Strawberry already examined,are frui ts in which thereceptacle takes part in their formation ; and they are

sometimes called false fruits or pseudocarps . In the

Apple (Fig . 1 55) the core is formed from the pistil , and the

pips are the seeds,while the fleshy part is formed from the

receptacle. Such a frui t is cal led a pome .

The Fig is a compound fru i t consisting of a hollow inflo

rescence, within which are numerous small drupes . The

P ine-apple is also a fleshy inflorescence , the axis of which iscontinued above and bears leaves . The Mulberry is formed

from a spike of many flowers the perianth-leaves of each

become united and fleshy ,and enclose the ovary, thus

resembling the Blackberry in appearance but di ffering

widely from it in origin .

The modifications found in frui ts have , in most cases ,an obvious connexion with the di spersal of seeds , the

various devices for which we will next consider .

CHAPTER XV I I

DISPERSAL OF FRUITS AND SEEDS

PRIOR to August 1 883 ,Krakatau , one of the East Indian

Islands, was covered with impenetrable forests . On

August 26 and 27 of that year , a violent volcanic eruption

occurred ; the topography of the island was completely

changed and the lava and molten ashes which fell upon

the remaining portions completely destroyed the vegetati on .

This provided a rare opportunity of studying the ways


in which a barren island (about twenty—five miles fromthe nearest mainland) acqu ired a new flora and fauna .

Coloniz ation of a barren i sland — It was found that the

first colonists were microscopic Blue—green Algae ,Bacteria

and Diatoms , which formed sl imy patches on the pumiceand ash

,and provided a sui table medium in which , later,

the spores of Ferns and Mosses germinated . All thesebodies are so very minute that they float as dust in theair , and are thus capable of being carried long distances

by the wind . In this way spores of these plants werecarried from the adj acent islands , and formed the firstelements of the flora . Then followed flowering plants

having light wind -borne fru its,and along the shore appeared

seedlings from seeds carried by ocean currents and washed

up by the sea ,many of them in logs of wood . The rotting

logs brought Fungi , and ,in the cracks Of the bark , small

animals . Birds visiting the island brought other seeds ,and lastly, man ’

s influence was seen in the introduction

of cultivated plants , and in the weeds that followed inhis train . In a few years ’ time

,large parts of the island

were again covered by rank and luxuriant vegetation .

Wind , water , and animals, especially birds , proved to be

the three principal agents concerned in carrying the seedsof a new flora to the island .

In a study of the modes of dispersal of the common

plants around us,we find the same agents at work and

an interesting collection may be made showing the various

devices by which Nature secures this end .

The obj ect to be attained is that seeds should be carriedfar enough away frOm the parent plant to prevent over

crowding , and to ensure that they are on sui table groundunoccupied by the same species . We will now study some

typical examples of dispersal mechanisms .

A . Dispersal by wind — The essential condition for wind

dispersal is lightness in proportion to bulk, or a floating

222 THE REPRODUCTIVE ORGANS

Groundsel,Dandelion (Fig . Col tsfoot (Fig . 1 56,

Thistles , Valerian , Bulrush ; and the perianth of the

Cotton -

grasses (Eri ophorum) (Fig . 1 58, 1 ) is transformedinto a tuft of long hairs . The Clematis (Fig . 1 56, 4 )and Mountain Avens have a long, persistent , feathery

style . The awn of the Feather-grass is twisted , and endsin a beautiful plume a foot in length . Some Anemoneshave hairy frui t- coats .

(5 ) Winged Seeds occur in the P ine (Fig . 1 56, Larch ,and cultivated climbers l ike Eccremocarpus and Bignonia .

(6) The Flattened Fru its of the Hogweed (Fig . 1 56, 6)spl i t into two thin hal f—fru its and are readily detached fromtheir slender threads during high winds .

(7 ) Many fruits have a Winged frui t - coat , and the frui ti s often flattened, e . g . Birch ,

Elm (Fig . 1 56, Common

Ash (Fig . 9,Sycamore (Fig . 20 2 ,

and Maple . The

wings of the Hornbeam (Fig . 1 56, 8) are formed frombracts . Most of these, however, are too heavy to be carriedfar , except during high gales .

(8) Globular Fru i ts and P lants may be rolled to a Slightextent by the winds

,as is the case with the fruits of

M edicago (Fig . 1 56, 9 ) and the whole plants of certainspecies of S elaginella .

(9) Censer Mechanisms . The capsules and follicles ofmany plants (Fig . 1 59, 1 to 5 ) are borne on erect stalks ,and the seeds can only escape from the cup- l ike fruit-casewhen violently shaken by the wind or by a passing animal

then a few seeds may be jerked out . Commonly the fruit

stalk decays , and the capsules with their seeds fall in a heapto the ground . We have already noticed the more im

portant ways in whi ch capsules Open to allow the seeds

to escape . Those widely open above are l iable to damage

by rain , but often the capsule is surrounded by teethwhich bend over and close the capsule in wet weather ,opening again when the air is drier (Fig . 1 59,

The frui t

FIG . 1 57 . WILLOWS IN FRUIT ; ALDE RS IN TH E BACKGROUND .

FIG . 1 58 . 1, FRUITS OF COTTON GRAS S ; 2

,P AP P OSE SEEDS

OF WILLOW H ERB .


and S ink to the bottom ; the rest of the plant may die

down , the species being renewed the next season by thebuds which then renew their growth . Such buds enablethe plants to tide over the winter , and are called WinterbudsC. Dispersal by animals Fungi growing in a pasture

commonly occur on the dung of browsing animals someof the spores may have been carried thither by the wind ,

but a common occurrence is that spores adhering to theleaves of plants are eaten by an imals and pass uninjured

through their food-canal . On the way they are partlydigested and this prepares them for germination . Some

fungus spores germinate with difficul ty until acted upon bya digest ive ju ice . The dispersal of such plants is in thefirst instance by wind ,

and in the second by animals which

further prepare them for germination .

(2 ) Birds sometimes carry seeds great distances in mudadhering to their feet .

(3 ) Fruits and seeds form an important food for many

birds . They are attracted by the bright colours of fleshyfruits , of which they eat the edible parts . Such fruits oftenhave either an indigestible , stony endocarp around the

seed ,as in drupes l ike the Cherry and Brambles a hard

frui t -coat,as in the achenes of the Strawberry or , where

the endocarp i s pulpy , as in berries , a hard seed -coat .While the fleshy parts are digested , the protected seedsOften escape ; they may pass through the food-canalof the bird , or be ej ected in the pellet from the crop .

By these means they may be carried some distance from

the parent plant and be capable of germinat ion . Thrushes

eating such frui ts often pick off the fleshy part and by

a jerk of the head throw the stones away .

Many examples of fleshy fru i ts are found in the hedgerows

, a fact which is especially interest ing when we

remember how important hedgerows are as nesting-places

DISPERSAL OF FRUITS AND SEEDS 22 5

for birds . Frui ts such as the following are commonly

to be found : Hawthorn , Rose ,Blackberry , Raspberry ,

Strawberry , Blackthorn ,P lum , Cherry , Crab ,

Mountain

Ash , Barberry , Gooseberry ,Guelder Rose, Wayfaring

Tree,Elder , Honeysuckle , Ivy, Dogwood , Holly, Spindle

Tree, Buckthorn , Woody Nightshade, White Bryony , and

Black Bryony .

(4) Animal s l ike the Sheep and goat often have largenumbers of hooked frui ts in their coats . S tructures of this

kind which have become entangled in the wool are called

FIG . 1 60 . HOOKED FRUITS .—I

, Cleavers ; 2 , 3 ,l

and 4 ,ach enes

of Avens showing the bend ing o f th e style to form a bo ok ; 5 ,

capitulum of Burdock with hooked bracts .

burrs ; some of them are entire fruits , others are hooks

only, the rest of the fruit having broken off . When thewool is eventually scoured and these foreign bodies wi th

the dirt are thrown on to the waste-heaps near the factoriesthe seeds often germinate . The plants that spring up

indicate the region from which the wool has been obtained .

If several kinds of hooked fruits are examined , i t wil lbe seen that the hooks are devel oped from differen torgans (Fig . 1 60 , 1

In the Cleavers (Fig . 1 60 ,Sanicle , and Enchanter

’

s

Nightshade, they are on the fruit~coat . In the Avens

(Geum) the style i s hooked (2 , 3, In the Burr Marigold1 296 p


they are barbed pappose bristles ; while those of the

Burdock (Fig . 1 60 , 5) are hooked bracts .

(5 ) In some cases Nuts of various kinds may be collected

as food by such animals as mice and squirrels and someof these may be left , which then germinate .

(6) Again , ants are act ive agents in fruit and seed

dispersal , especially in the case of those seeds which have

oil -bodies attached to them . Th is is well seen in the Gorse

(Fig . 1 61 ,and more clearly still in the Castor Oil seed

S imilar Oil-bodies occur in many plants , e

'

. g . Cow

Wheat, Cornflower , and several fruits of Sedges, Rushes ,

F IG . 1 6 1 . SEEDS WITH OIL-BODIES .

I , Gorse ; 2 , Castor Oi l ; 0 , Oi l-body .

and Grasses . The ants eat the Oil-body, and throw the

seeds away along an ant-run , lines of such plants may be

found grown from seeds which have been dropped by ants

on their way to the nest . The process may easily beobserved if such seeds are laid in their track .

D . P ropulsive mechani sms — In addition to the modesof dispersal already mentioned, many plants possess

devices which render them independent of wind, water , oranimals as carrying agents . ( 1 ) Often ,

as the fru i t ripens anddries , tensions are set up in the fru it -coat , whi ch resul t

in a sudden bursting , whereupon the seeds are shot outsometimes several feet .


(2 ) The turgidi ty of part of the fru i t -coat or seed is

the means of expelling many seeds . Interesting examples

to observe are theWood Sorrel (7) and the Balsam In

the former each seed has a fleshy aril , the inner layer ofwhich is very turgid . If the ripe fru i t is disturbed

, th e

capsule spl i ts , the aril suddenly turns inside out,and

the seeds are shot some distance . If the ripe fruits of theBalsam are l ightly pressed between the fingers , the frui t

coat splits and the valves roll up inwards wi th great force ,

scattering the seeds in all directions .

PART III

SYSTEMATIC BOTANY

CHAPTER XV I I I

CLASS IFICATION OF PLANTS

IN the preceding chapters we have investigated the

structures and functions of the organs which const itute a

plant the development of plants and their perpetuat ion .

In the course of our study we have met with many indi~

viduals, and occasionally analogies and differences havebeen pointed out . But , so far

,no general attempt has

been made to Classify and arrange the two hundred thousand or so members of the vegetable kingdom . How are

we to discover the basis of a satisfactory classification ?

The question obtains its most interesting solution in a

review of the history of botanical science .

H i story of systemati c botany— There is litt le doubt that

in the early dawn of civilization the cu lture of plants was

studied from the utilitarian point of V iew : by the agri~

culturist to provide food for himself and his flocks and

herds , and by the physician to prepare usefu l medicines .Among later nations , and especially among the Greeks

and Romans, the subject assumed a new aspect attempts

were made to systematize the vegetable kingdom from the

data and facts which had accumulated and been recorded

23 0 SYSTEMATIC BOTANY

during preceding centuries . But beyond the subdivi sionby Aristotle and Theophrastus into Trees

,Shrubs , and

Herbs , this branch of our science was practically dormantuntil the sixteenth century.

The beginning of a scientific system i s indi cated in thecelebrated Herbal of John Gerard

,but to better advantage

in the De P lanti s of Andreas Caesalpinus, who divided thevegetable kingdom into fifteen classes , each distinguishedby a typical frui t. Other distingu ishing characters wereintroduced by subsequent writers . John Ray dividedflowering

’

from flowerless plants , and suggested the

terms Monocotyledons and D icotyledons as prime divisions

of the former . Robert Morison considered the structuresof the flower and of the fru it and De Tournefort proceededto more detai l by taking the corolla into account .

The i llustrious Swedish botanist , Carl Linné, betterknown by the latin ized form of his name

,Linnaeus , now

enters into our brief review . He introduced a classification

based upon the reproductive organs, i . e . the stamens an dpistil . The effect of the Linnaean system on systematic

botany cannot be over-estimated ,and although the system

in detail was subsequently replaced by others , the lines

of thought and nomenclature which he developed are

fundamental .The Linnaean system was artificial the natural affinities

and relations of plants were ignored , although the authorwas aware that these considerations were essential to a

correct classification of the vegetable kingdom . It foreshadowed a natural system

,a system which would exhibit

a continuou s sequence of plant - life , from the lowest vege

table organisms to the most elaborated members of the

plant world . Such a system cou ld not be derived from

a study of the functions and forms of one or more SpecialOrgans of plants it could only be deduced from a studyof the forms and development of these organs .

232 SYSTEMATIC BOTANY

ovary before pollination . Such seed-plants are includedin a division called Gymnosperms (Gr . gymnos naked)and are a very ancient type .

Seed-plants like the Buttercup , Primrose, and Bluebell ,produce their ovules in an ovary formed of closed carpels ,and belong to a more modern group called Ang iosperms

(Gr . angei on a vessel) to this group belong the greatmaj ority of the seed-plants of the vegetation of the presentday . In the Stock and Primrose the parts of the flower '

are in fours or fives , and the seeds contain two cotyledons .Such Angiosperms are placed in a class called Di cotyledons . On the other hand , the parts of the flowers of theBluebell and Crocus are in threes , and the embryo of theseed has only one cotyledon . Such Angiosperms form the

class Monocotyledons .

These classes are further subd ivided according to the

relat ionships of the parts of the flower . Dicotyledons

with a simple perianth of free petals in one or two whorls

are known as Arch ichlamydeae (Gr . arche beginning ,chlamys a mantle) , while those with a more highly

developed perianth , in two whorls , the petals being j oined

together by thei r edges to form a gamopetalous corolla ,

are called Metachlamydeae (Gr . meta beyond) or Sym o

petalae (Gr . syn together) .

Other subdivisions depend on ( 1 ) the relations betweenstamens and pistil , whether the former are hypogynous ,perigynous , or epigynous and (2) the condition of theovary, whether apocarpous or syncarpous— one or morecelled .

We thus see that the characters of most importance inclassification are those to be noticed in a careful examination o f the parts of a flower from outside inwards . The

classification of the above-mentioned plants may be shownas follows

CLASSIFICATION OF PLANTS 233

S PERMAPHY'

I‘

A

Gymnosperms Angiosperms

Dicotyledons Monocotyledons

Arch ich lamydeae S ympetalae

apocarpous superior superior

P INE BUTTERCUP P RIMROS E BLUEBELLLARCH

inferior Inferi or

DAIS Y CROCUs

The Study of a localflora .

—~A book dealing with the plantsof a country or a district

,in which the species are arranged

and classified in the manner indicated , is called a F lora .

In the study of the vegetation of your district you will findit more interesting and profitable to devote your attention

to the plants of one habitat at a time, than to collect plants

indiscriminately. Always have an object in V iew and followi t with care and intelligence . In each habitat probably oneor only a few species , which are best adapted to i t

,will

predominate. These are the plants you should study first

and most carefully, neglecting for the time being the rarer

ones . Distinguish between social species , i . e . plants of

the same kind growing together in large numbers ; and

those which occur sparingly ; also between the large sturdytrees and shrubs and the plants growing under their shadeand protection .

Note in detail the form, mode of growth , and the struc-1

ture of the leaf , and see whether these bear any relationto the plants

’

environment , such as soil , water-supply,humidity, altitude , and exposure to sun and wind . You

will find that , in nature, plants group themselves into plant-i

s oc ieties and associati ons according to the conditions‘of the habitat (Fig .


By means of a Flora determine the species carefully and

try to arrange the plants found in the order of importancei n the vegetation : first the dominant ones , then the froquent and occasional ones , and so on in descending order .A collection of the characteristic species should be madeand classified according to habitat . Each should bear

a label giving the following particulars natural order,

genus , species , plant-association or society, position in theassociation (i . e . dominant or otherwise) , locali ty, and date.

Study in the same way the plants of several different

habitats , and contrast the types . In time you will learn

to recognize all the more important species and the moreinteresting facts concernIng thei r distribution .

CHAPTER XIX

CLASS 1 , DICOTYLEDONS

ARCHICHLAMYDEAE

Dicoty ledons are distinguished by having the vascularbundles of the stem arranged in a ring , the leaves are

net-veined , the partS'

of the flower are in whorls of fouror five, and the embryo of the seed has two cotyledons .

This class is much larger than that of the Monocotyledons . The broad, net-veined leaf is very characteristic ;secondary thi ckening is general . Dicotyledonous treesform the great deciduous forests of Temperate regions ;the evergreen shrubs and peculiar xerophytes of semidesert and desert regi ons belong largely to this class,and many of the species forming the rank vegetation of

Tropical forests are also Dicotyledons .

DICOTYLEDONS : ARCHICHLAMYDEAE 235

The Dicotyledons are di vided into two great di vi sions .The fir st , Archichlamydeae , includes plants whi ch havea relatively simple type of flower . The natural orders ofthis division embrace flowers increasing in complexityfrom primitive forms like Willows and Buttercups , withmany stamens and much pollen , up to the more highlyspecialized forms l ike the Sweet-Pea and Violet, or, as inthe Hogweed and Chervil , to smal l epigynous flowers

rendered attractive by being massed into compact inflorescences . The second division , Metachlamydeae , is characteri z ed by the petals being joined into a flower- tube, as

in the Heath and P rimrose,accompanied by reduction

in the number of stamens and greater economy in the

production of pollen and honey, culminating in the aggre

gate flower-heads of the Daisy and Dandelion . In this

chapter we shall deal only with the first di vi sion .

(A.) Archichlamydeae . The distinctive features of this

division are : the parts of the perianth are either absent ,or in one or two whorls ; the inner whorl of petal s is free

(i . e . the flowers are polypetalous) .

Order SALICACEAE . Trees with unisexual flowers in

catkins,flowers dioecious , perianth absent . Flowers

of the male catkins have two or more stamens in the

axil of a bract . Flowers of the female catkins havetwo carpels in the axil of a bract syncarpous ovules

indefini te . Fruit a capsule. Seeds with a tuft of

hairs at the base (see Fig . 1 85 , p .

The Willows , Sallows, and Osiers are abundant in theNorth Temperate region , especially in low-lying, wet

areas . Many are pollarded (S alix alba, &c . ) others arecoppiced (S . viminalis) , and used for basket-making

(see p . On mountai ns in Britain , in the Alps, and in

Arctic regions , very small creeping forms occur, only one

or two inches high , e. g . S alix herbacea and S . reticulata .


The P oplars (P opulus) also belong to this order (see Fig .

Order BETULACEAE .

1 Shrubs or trees with srmple

stipulate leaves . Flowers in terminal catkins . Monoe

cions , and usually arranged in small three-flowered

cymes in the axils of the bracts of the catkin (Fig .

Perianth reduced . Ovary inferior carpels two ,syn

carpous , two- celled , one ovule in each cell . Fru i t a oneseeded indehiscent nut .

This order includes several well-known trees, e . g . Birch

(Betula alba) , Alder (Alnus glutinosa) , Hazel (Cory lusAvellana) , and Hornbeam (Carp inus Betulus) (see Figs . 1 87 ,1 88, 1 89, pp . 282

Order FAGACEAE .

1 Trees with simple stipulate leaves .Flowers in axil lary catkins , monoecious . Perianthlobes 5—6 . Carpels three, syncarpous . Ovary inferior,usually three -celled with two ovules in each . Frui ta one-seeded nut . Nuts enclosed in a cupule (seeFig . 1 9 1 ,

p .

The order includes many forest trees , e . g. Oaks (Quercusspp.

2) , Beech (F agus sylvati ca) , and Sweet Chestnut (Castanea saliva) .

Order RANUNCULACEAE . The perianth is indefinite, oftenpetaloid and polypetalous . S tamens indefinite and

hypogynous . P istil superior . Carpels indefinite and

usually apocarpous . Fru i t a group of achenes or

follicles (Figs . 1 44 and The flowers may be

cyclic : Aqui legia ; hemicyclic : Ranunculus acyclic

or spiral Aconitum,Helleborus .

The plants of this order are chiefly North Temperate,

1“

Th e orders B etulaoeae and F agaceae are very c losely related ,and sometimes p laced in one order, Cupuliferae.

2 Spp . after a generic name means th ere are several species ineth e genus .


hood,enclosing two nectaries , which are modified petals .

In the two latter the flowers are zygomorphi c . Floral formula : K 5 or 3 , C 0 —5 or 0 0

, A 5— oo, G I

— Oo.

The nectaries Of the Christmas Rose, Winter Aconite

(Eranthis) ,Love- in—a-Mist (Nigella) Monkshood, and Aconiteare known as honey-leaves and are probably derived

from stamens .

Order CRUCIFERAE . Sepals and petals four each . Sta

mens six , in two whorls, two outer short , and fourinner long ones (tetradynamous) . P istil superior of

two carpels (syncarpous) , two- celled , divided bya partition (replum) . Fru it , a siliqua or Sil icula

(Figs . 1

This order contains upwards of 2 0 0 genera and

species widely distributed throughout the North Temperateand Medi terranean regi ons . They are mostly herbaceous

perennials , but some are annual s , and others are biennial s .The leaves are without stipules ; the inflorescence i sa raceme or corymb , and is usually without bracts .Very many cul tivated plants belong to this order

, e. g .

the Cabbage (Brassica oleracea) , from which many useful

varieti es have been derived by cultivation and selection,

such as Red Cabbage ,Kale, Savoy, Brussels Sprouts , in

which the axillary buds become smal l cabbages . In theBroccol i and Cauliflower the inflorescence becomes abnormal ly branched and fleshy, and the Kohlrabi is a tuberous

stem or corm .

From other species of Brassica are derived the Turnipand Swede ; the Radish , Horse-Radish ,

Watercress ,Garden Cress , and Mustard , also belong to this order, as

well as some of the commonest weeds of cul tivation ,e . g ,

Charlock and Shepherd’s Purse ; whi le others are cultivated for their flowers

,for example ,

Wallflower , Stock ,Candytuft , Honesty, Arabis, and Aubretia .


Order CARYOPHYLLACEAE . Herbs with opposite leaves ,nodes swollen , inflorescence a dichasium or scorpioid

cyme . Flowers regular . Sepal s 4 -5 . Petals 4—5 ,

usual ly white or pink . Stamens 8—1 0 , the outer

whorl usually opposite the petal s , hypogynous or

sometimes perigynous . P istil syncarpous , one-celled ,placentation free central , ovules indefinite, styles 2—5 .

The embryo of the seed is curved and surrounds the

perisperm .

The order is a large one, and includes many famil iar

plants , both wild and cultivated . Many species occur inBri tain in very varied habitats , as often suggested by their

common names , e . g .

Water Chi ckweed (S tellari a aquati ca) , Bog S titchwort (S . uli

ginosa) . On th e coast we have : S ea Campion (S i lene mari tima) ,S ea P urslane (Arenari a peploi des) , S ea Spurrey (Spergulari a rupe

stri s) , S ea P earlwort (S agina mari tima) . On th e mountains : S eaCampion

, (S i lene mari tima) , and alpine spec ies of Ch ickweed (Cerastium alpinum) , Moss Campion (S i lene acauli s) , Alpine Campion(Lychni s alpina) , P earlwort (S agina On walls , rocks , drybanks , and fields P inks and Carnations (D i anthus Ch ickw eeds ,

Sandworts and P earlworts .

In moist woods and h edgebanks : R ed Campion (Lychni s di oi ca) ,Ragged Robin (L . F los-ouculi ) , Greater S titchwort (S tellari a H olo

stea ) , Wood S titchwort (S . nemorum) . As weeds o f cu ltivationBladder Campion (S i lene i nflata) , Corn Cockle (Ly chni s Gi thago) ,Chi ckweeds (S tellari a medi a , Corn Spurrey (Spergula arvensi s) .

Many plants of this order are readily distinguished by

their opposite, entire leaves and swollen nodes , and al so

by the inflorescence, which is very characteristic . The

main axis ends in a flower (Fig . 1 65 , In the axils of

the pair Of leaves below , branches arise, each of which

bears a pair of leaves . In the axils of the latter leaves ,branches arise as before, and so the processmay be repeated .

The name dichas ium or false di chotomy i s given to

this type of inflorescence . Sometimes one of the branchesat a node outgrows the other , and in the later branches


FIG . 1 65 . I , FLORAL D IAGRAM OF LY CHNIS ; 2 , INFLORE S CENCEOF CERAS TIUM ; 3 ,

D IAGRAM OF A MONOCHAS IAL CYME ; 4 , VER

TICAL SECTION OF MALE FLOWER OF RED CAMP ION ; 5 , V E RTICALSECTION OF FEMALE FLOWER OF RED CAMP ION ; 6 ,

FRUIT OF

D IANTHUS an , androph ore ; br , bract ; c,calyx ; co , corona ;

t,teeth Of capsu le .


tongued insects , such as bees , moths , and butterflies . The

fruit is a capsule opening by four to ten teeth (Fig . 1 65 ,

and the seeds , ornamented with wart- like outgrowths,are dispersed by wind or animals (see p .

The Red Campion (L . di oi ca) is dioecious the female

plant also differs from the male plant by i ts larger S izeand coarser growth . Some species with white flowers

,

e . g . Night -flowering Campion (S i lene noctiflora) , are closedduring the day , but are open and sweet -scented at night ,and are visited by n ight-flying moths .

The flower—stalks of the Catchfly are covered with st ickyhairs , to which numerous small insects adhere

,hence its

name .

The Stitchworts,Chickweeds , and Sandworts differ from

the preceding in having a polysepalous calyx , a wider ,more Open flower , and honey accessible to Short - tongued

insects . Some , like the Chickweeds , are able to pollinatethemselves . Sometimes the petals are so deeply cleft that

the corolla appears to have eight or ten petals . In the

St itchworts,Pearlworts

,and others

,we often meet with

reduced flowers

Order ROSACEAE . Leaves usually stipulate , receptaclemore or less hollowed

,sepals and petals four or five

each,stamens indefinite ,

perigynous , ovary usually

superior and apocarpous (Fig . 1 66, 1 ) sometimes (e . g .

Apple) i t is inferior and syncarpous

There are ninety genera and upwards of two thousandspecies in this widely distributed order . It contains many

familiar and cultivated species , including a large numberof our common fru i t trees and Shrubs . Many spread

rapidly by vegetat ive reproduction , e . g . the Strawberry,S ilverweed , and the Blackberry by runners , and the Raspberry by suckers (Fig. 27 , p .

The flowers resemble those of Ranunculaceae,but are


distinguished from them by the hollow or concave recep

tacle, perigynous calyx , corolla , and stamens , and by thefact that these parts of the flower are in whorls and notspirally arranged . The form of the receptacle and the

mode of origin and structure of the fruits of this orderare interesting ; and the following Should be studied as

showing transitions from perigynous to epigynous , and

apocarpous to syncarpous flowers and fruits . TheMeadowsweet (Sp irea Ulmaria) has a nearly flat receptacle the frui t

FIG . 1 66 .

1 , FLORAL D IAGRAM OF P LUM ; 2, FLORAL D IAGRAM OF AP P LE .

is a group (aeterio) of two-seeded , twisted follicles . The

Tormentil (P otenti lla erecta) has a persistent calyx and

also an epicalyx ; the receptacle is convex in the middle

and bears many dry, one- seeded achenes . The Strawberry

(F ragaria vesca) has an epicalyx (Fig. 1 1 3 , I ) , and the centralconvex part of the receptacle enlarges in the fruit , becomes

fleshy, and bears the dry achenes on the outside of it .

The Blackberry (Rubus fruti cosus) and Raspberry (R .

Idaeus) have no epicalyx and the column rising from the

centre of the flat receptacle bears an aeterio of drupels

Q 2


(see Fig . The achenes of the Mountain Avens (Dryasoctopetala) have a persistent feathery style for wind-dispersal ; and in the Water Avens (Geum rivale) the stylebecomes hooked and the frui t is dispersed by the fur of

animals (Fig . 1 60 ,2,

The Lady’

s Mantle (Alchemi lla

vulgari s) h as very smal l , crowded , green, much- reduced

flowers the calyx is four or five lobed , there are no petals ,only four stamens , and one or two carpels enclosed in a dryhollow receptacle . Th e Salad Burnet (P oterium Sangui

sorba) has no corolla , the flowers are monoecious and

crowded into a head , the upper ones are female withfeathery stigmas , the lower Ones are male with manystamens , the pollen is dry and carried by the wind . The

Dog-Rose (Rosa canina) has a deep , hollow receptacle con

tracted above and enclosing several achenes (Fig .

In the Apple (Py rus M alus) the five carpels are syncarpous

and inferior , and uni ted to the fleshy receptacle (Fig.

Other familiar pome fruits are Pear (Py rus communi s) ,Quince (Cydonia vulgari s) , Cotoneaster , Rowan (PyrusAucuparia) , and Hawthorn (Crataegus Oxyacantha) .Thus we get development from perigyny to epigyny

in Meadowsweet , Torment il , Blackberry,Rose , Cherry ,

Apple,and Pear from apocarpy to syncarpy in Meadow

sweet , Torment il , Blackberry ,Cherry

,Apple

,and Pear ;

and fruits of special interest in Avens , Rose , Strawberry ,

Blackberry ,Cherry,

and Apple (see pp . 2 1 7— 1 9 and

Order PAP ILIONACEAE (LEGUMINOSAE ) . Leaves stipu

late,flowers in racemes

,papilionaceous . S tamens ten

,

perigynous , united into a tube by their filaments

(monadelphous) or nine united and one free (diadel

phous) . P ist il of one carpel,superior

,apocarpous .

Frui t a legume (F ig .

Papilionaceae is a sub -order of Leguminosae . In the

latter order are included such species as the Acacias , the

SYSTEMATIC BOTANY

to pollination by bees (see p . 1 88 , where a full descriptionof a papilionaceous flower will be found) a few are self

pollinated,e . g . Edible P ea (P i sum sativum) , and species

of Vetch (Vicia) , some of which have cleistogamous flowers .

In the Gorse (Ulex europaeus) (Fig . the Petty Whin

(Genista angli ca) , Laburnum (Cy tisus Laburnum) (Fig .

Rest-harrow (Ononis arvensi s) , and Lupin (Lup inusthe stamens are monadelphous

,and the flowers have

no honey,al though the Broom has honey- guides In

others the stamens are diadelphous,e . g . Clover (Trifolium

Bird’s - foot Trefoil (Lotus corni culatus) , Vetches and

Tares (Vicia Pea ,Bean (Vi cia Faba) , Scarlet-Runner

(P haseolus multiflorus) , and Sweet Pea (Lathyrus odoratus)(Fig . The seeds are usually rich in proteins and

starch stored in the cotyledons,and form important food

stuffs, e . g . Pea , Bean , Pulses . In some, like the Kidney

Bean,the pods are eaten . Many are valuable fodder

plants , e . g . species of Vetch , Tare, Clover , Medick ,and

Sai nfoin . The Groundnut or Peanut (Arachi s hypogaea)develops its pods underground .

Order UMBELLIFERAE . Flowers usual ly In compound

umbels , Often zygomorphic . Sepals and petals usually

five each . Stamens five, epigynous . Ovary inferior,of two carpels, syncarpous, and on the ovary a honeysecreting disk . Fruit a cremocarp , which splitsinto two half-fruits (mericarps) (Fig .

This order i s remarkable in having small flowersmassed into dense , usually compound , umbels, rendering

them very conspicuous , and by means of this character

most plants of the order can be readily identified (Figs . 1 1 9and Many of the species are poisonous

,e . g . Hem

lock (Conium maculatum) others,like the Carrot (Daucus

Carota) and Parsnip (P eucedanum sativum) , are edible, and

largely cultivated for their fleshy roots . In the Celery


(Apium graveolens) the leaf—stalks are etiolated by banking

up with soil and so rendered white and tender .

Other examples are the Common Parsley (Carum P etro

selinum) , Caraway seeds (the fruits of Carum Carui ) ,Aniseed (the fruits of P imp inella Anisum) , and Corianderseeds

’

(the fruit s of Corian'

drum sativum) . Samphire

(Crithmum mari timum) and Fennel (F oeni culum vulgare)occur on sea cliffs

, and the Sea Holly (Eryngiummari timum)on sandy Shores . Some, l ike the Chervil (Chaerophyllum

FIG . 1 68 . FLORAL D IAGRAM OF H ERACLEUM .

sy lvestre) , are troublesome weeds in meadows . Severalspecies are marsh plants

,e . g . Marsh Pennywort (Hydro

cotyle vulgari s) , Wild Celery (Ap ium graveolens) , Dropwort s(Oenanthe On stream—sides occurs Sweet Cicely

(Myrrhi s odorata) , and several are common in fields andhedgebanks, e . g . Fool’s Parsley (Aethusa Cynap ium) ,Hogweed (Heracleum Sphondylium) , Earth -nut (Conapodium denudatum) , and Hedge Parsley (Caucali s Anthri scus) .Usually the fruits consist of two flattened mericarps

,


and are dispersed by the wind (see Fig . 1 48 , p . In

theWood Sanicle (Sani cula europaea) the fruits are hookedand dispersed by animals .

The Archichlamydeae includes upwards of sixty thousandspecies . The more primitive forms are distinguished fromthe higher ones by the parts of the flower being indefinite

in number and spirally arranged on the axis . The corolla ,

when present , is usually polypetalous , and the ovules have

two coats . In Ranunculaceae the flower is hypogynous,and the perianth in some species is spiral : in others

,

cyclic . The stamens and carpels are in general spirallyarranged and indefinite . In Cruciferae all the whorls are

cyclic . In Rosaceae and Papilionaceae the flowers are

perigynous , and in the latter order they are irregular . Inthe Umbelliferae many small irregular epigynous flowersare massed together in conspicuous umbels . The divisionis very complex , and the characters , even within a single

order , may be very variable .

CHAPTER XX

DICOTYLEDONS

B . METACHLAMYDEAE OR SYMPETALAE

IN this division the perianth i s in two whorls,and the

petals are united (gamopetalous) .

Order PRIMULACEAE . Flowers often on scapes , usuallyregu lar . Sepals five . Petals five , united . Stamensfive , epipetalous and opposite the petals . Ovary

25 0 SYSTEMATIC BOTANY

Many species flower in the early spring, and are commonon the mountains . Rosette- forming species are frequent ,Alpine forms like Androsace form compact cushions

,and

the l ittle Soldanellas send up their flowers through the

snow. Many grow in wet places, e . g . Brook-weed , Loose

strife (Lysimachia) , Creeping Jenny (L . Nummularia) , andthe Bog P impernel (Anagalli s tenella) , which occurs inpeaty bogs . The Water Violet i s an aquatic plan t with

finely divi ded leaves which hibernates by means of winterbuds . The Scarlet P impernel (A . arvensi s) is a cornfieldweed , and the Sea Milkwort occurs in salt -marshes . The

Chickweed Wintergreen (Trientalis) grows in heaths andupland heathy woods .

Order BORAGINACEAE . Mostly herbs with alternate

exstipu late leaves ; usually rough with hai rs . Flowersoften showy in single or double scorpioid cymes

which are coiled when in bud ; the flowers as they

open all face the same way (Fig . 1 70 , Calyx five

lobed . Corolla regular, hypogynous , tubular, lobesfive, Often spreading ; throat more or less closed by

projecting scales or hai rs . Stamens five, epipetalous .

P istil of two carpels, style gynobasic (Fig . 1 70 ,

Frui t four one- seeded nutlets (Fig .

Th e more familiar spec ies are : Forget-me-nots (Myosoti sComfrey (Symphy tum ofii cinale) , Borage (B orago ofii cinali s) ,Evergreen Alkanet (Anchusa sempervi rens) , H ound

’

s -tongue(Cynoglossum ofi cinale) , Lungwort (P ulmonari a ofli cinali s) ,V iper’s Bugloss (E chi um vulgare) .

The flowers of most species show interesting colourchanges during their development , as suggested by the

name of one of the Forget -me—nots (My osotis versi color) ,which is at first yellow and then blue and violet . Others

are white, then change through red to blue , while the

Lungwort and Viper’s Bugloss are red when young , changi ng

DICOTYLEDONS : METACHLAMYDEAE 2 5 1

later to violet and blue . The flowers are vi sited by flies ,bees , and moths , an d the honey is protected by the narrow

tube and overhanging scales or hairs .

Borage and Comfrey are typical bee-flowers . They are

FIG . 1 7 1 . FLORAL D IAGRAM O-F

FORGE T-ME -NOT.

FIG . 1 7 0 . FORGET-ME -NOT.— I , in

florescence 2 , pistil 3 ,vertical section

f flower ; co,corona .

pendulous , and the cone of stamens showers po llen on thehead of the vi siting bee in a manner similar to that of theHeaths . The Lungworts have dimorphic flowers , with

long and short styles , as in the P rimrose, and the corolla


tube is closed by five tufts of hairs between the stamens .

The fruit of the Hound’s- tongue is provided with recurvedhooks

, as is also the calyx of the Forget -me-not , wh ich

serve as a means of fruit -dispersal by animals .

Order LAB IATAE . Stem square leaves Opposite flower

zygomorphic . Sepals five, united . Petals five , united ,two - lipped . Stamens usually four

,two long and two

short (didynamous) , epipetalous . P istil of two carpels ,superior, syncarpous , each carpel divided into two cells .Ovary four - lobed

,wi th the style springing from the

base (gynobasic) . Fruit usually four nutlets (Fig .

There are about 1 5 0 genera and species in this

order . They are very frequent in the Mediterranean region ,where many shrubby forms occur which are xerophytes

with heath- like habit and back- rolled , hai ry leaves . Manyare scented , due to volati le oi ls secreted by epidermal

glands , and are often cu lt ivated and used as condiments ,or for thei r o ils or perfumes , e . g . Lavender (Lavendula

vera) , Rosemary (Rosmarinus ofli cinali s) , Thyme (Thymus

vulgari s) , Mint (M ontha vi ri di s) , Peppermint (M . piperi ta) ,Marj oram (Origanum vulgare) , Garden Sage (Salvia ofli ci

nali s) .Vegetative reproduction is common

,as in the Garden

Mint . The square stem and opposite decussate leaves are

very characteristic . The primary inflorescence\

is usually

racemose , but the later branches are cymose . In some,

condensed cymes occur at the nodes and , overlapping theleaf-axi ls

, give rise to false whorls of flowers called vert ici llasters (Fig . 1 72 ,

The flowers are adapted chiefly to

bees (Fig. 1 72 , and some to moths and butterflies . The

simpler flowers with shorter tubes,e . g. Thyme and Gipsy

wort , are vi sited by miscellaneous insects . The HenbitDeadnettle (Lamium amplexi caule) produces cleistogamousflowers .


Many species may be found in pastures, meadows , andhedgerows in Britain

,e . g

Ground Ivy (Nepeta hederacea) , S elf-h eal (P runella vulgari s) ,H edge Woundwort (S tachy s sylvati ca) , Wood Betony (S . ofli cinali s) ,Wh ite Deadnettle (Lami um album) , Red Deadnettle (L . purpureum) ,Yellow Archangel (L . Galeobdolon) , Wood Sage (Teucrium S coro

doni a) , Bugle (Ajuga replans) .S ome are common cornfield weeds , e . g . H emp Nettle (Galeopsi s

Tetrahi t) , Corn Mint (M entha arvensi s) .Others are marsh p lants , e . g . Marsh Woundwort or Water Mint

1M . aquati ca ) , Greater Sku llcap (S cutellari a galeri culata) , G ipsywort (Lycopus europaeus) .

Order SOLANACEAE . Flowers usually regular . Sepalsfive, united . Petals five , united . S tamens five , epi

petalous anthers often united . Carpels two ,syncar

pous , and placed obliquely. Ovary two-celled , ovu lesindefinite style terminal . Fruit a capsule (e . g .

Henbane ) , or a berry (e . g . Bittersweet and Potato)

(Fig .

The leaves are alternate, but in the inflorescence, as a

result of fusion and displacement (adnation) , two leavesoccur apparent ly at the same node . The flowers are

usually regular , but a few are zygomorphic , and form a

t ransition to the order Scrophulariaceae .

Only four species grow wild in Britain , one of which , theWoody Nightshade (Solanum Dulcamara) (Fig . is

common in hedgerows , but many are familiar in cu ltivation .

A large number occur in Central and South America,from

whence we have Obtained such plants as the Potato (S olanum tuberosum) , P etunia,

Winter Cherry (P hysali s

and Tobacco (Ni cotiana Tabacum) . The flower of the

Tobacco has a very long corolla—tube, and i s pollinated by

long- tongued moths .Many species are poisonous or narcotic , a property which

is due to the presence of such alkaloids as atropine , the

active principle in belladonna,nicotine, and hyoscyamine,

DICOTYLEDONS : METACHLAMYDEAE 255

which are derived from the roots , leaves , or seeds of theplants after which they have been named , namely AtropaBelladonna (Deadly Nightshade) , Niootiana Spp. (Tobacco) ,and Hyoscyamus niger (Henbane) . The latter is common

in waste places in Britain and occasionally in such places

is found the poisonous Thorn-apple (Datura S tramonium) .The Tea- tree (Ly cium chinense) is frequent in hedgerows but , unlike the B ittersweet , is not a nat ive of Britain .

FIG . 1 73 . FLORAL D IAGRAM OF WOODY NIGHTSHADE .

Cayenne pepper is Obtained from pods of species of

Capsi cum. Some fruits are edible, e . g . Tomato (SolanumLy c

'

opersi cum) . The Mandrake (M andragora ofli cinali s) ,connected with which are so many strange superstitions ,also belongs to this order .

Order SCROPHULARIACEAE . Flowers zygomorphic, very

variable sepals five , united . P etals five,united, often

two- lipped . Stamens four,two long and two Sho rt

(didynamous) , somet imes only two , epipetalous . P istilof two carpels , superior , syncarpous . Ovary two- celled ,style terminal (Fig .


This order contains many poisonous species and is closelyrelated to Solanaceae,

but u sually the flowers are irregular

and the ovary is not oblique . Many species occur inBritain

,and they possess interesting peculiarit ies both in

vegetat ive and reproduct ive organs . Several are semi -parasites (See pp . 358 e . g . species of Eyebright (Euphrasi a

Bartsia ,Lousewort (P edi culari s Yellow Rattle

(Rhinanthus and Cow-wheat (M elampy rum

The Speedwells (Veroni ca) occu r in varied habitats .

The Water Speedwell (V . Anagalli s) , Marsh Speedwell

(V . scutellata) , and Brooklime (V . Beccabunga) are marsh or

aquat ic . Several species are common cornfield weedswhi le the Germander Speedwell (V . Chamaedrys) is commonon hedge-banks and others occur on heaths and mountains . In gardens many New Z ealand shrubby species

are cult ivated ,which are curious xerophytes with small

compact leathery leaves resembling species of Cypress , Box ,and other evergreens .

Other common species are Toadflax (Linaria Snap

dragon (Antirrhinum Spp. ) (Fig . 1 74, 4 , Figwort (S crophularia Foxglove (Digi tali s purpurea) (Fig . 1 74 ,

Musk,

and Monkey Flower (M imulus the latter havi ngsensit ive stigma- lobes which quickly close when touched .

The flowers of the Foxglove are all brought to one side by

the bending of the flower- stalk . The Ivy- leaved Toadflax

(Linaria Cymbalaria) has flowers which turn to the light ,but after pollinat ion ,

turn away, and the flower- stalk grows

and presses the fru its into crannies where they ripen and

shed their seeds . The Figwort s are pollinated by wasps .

The st igma ripens before the anthers , and the stamens andstyle lie on the lower lip of the flower .

The following flowers should be compared as to number

and posit ion of stamens : Mullein (Verbascum Thapsus) ,five stamens (Fig . 1 74 ,

Figwort and P entstemon,four

stamens and a staminode Toadflax,Snapdragon

, and


Foxglove (Fig . 1 74, four stamens and somet imes a

stami node in the two former . Veroni ca has only twostamens (Fig . 1 74, 3 and Fig .

Order CAPRIFOLIACEAE . Mostly shrubs or trees,leaves

decussate, usually exst ipulate . Flowers in cymes,

regu lar , somet imes irregular, usually showy , epigynous .Calyx five- toothed . Corolla five- lobed . Stamens five

(or four to ten) , epipetalous . Carpels two to five,

synca rpous . Ovary inferior , one to five- celled , with oneto many ovules in each cell . Fruit usually a berry or

a drupe (Fig . 1 75 ,

This order includes a number of shrubs well known in

cultivation , several of which are found wild in Britain,e . g .

Elder (S ambucus nigra) , Guelder Rose (Vi burnumOpulus) ,Wayfaring Tree (V . Lantana) , Honeysuckle or Woodbine

(Loni cera P eri clymenum) , the Snowberry (Symphori carpusracemosus) , Weigelia (Di ervi llaflorida) . Several others are

common in shrubberies .

The Elder has compound , pinnate , and stipu late leaves

small regular hermaphrodite flowers in umbellate cymes ;and the fruit i s a drupe wi th one to five stones .

The Guelder Rose has simple leaves with small glandular

stipu les , and cup- like extra floral nectaries on the leaf—stalk

(Fig . 2 1 9, The flowers are in coryrnbose cymes and

Show an interesting division of labour (Fig . 1 75 , The

outer flowers of the inflorescence are neuter,with large

,

attractive ,irregular corollas but they have neither

stam ens nor pistil (Fig . 1 75 , The inner flowers aremuch

smaller and perfect (Fig . 1 75 , 4 and producing bright

red drupe- like fruits each with one stone . In the cult ivatedform of Guelder Rose all the flowers are neuter and havelarge corollas .The Wayfaring Tree is a characteristic shrub of the

woodlands on calcareous soil . The young shoots are

FIG . 1 75 . GUELDER ROSE .— I

,floral d iagram ; 2

,portion o f

inflorescence ; 3 , neuter flower ; 4 ,perfect flower ; 5 , verti ca l

section Of same .


The characteristic feature of the order is the highlyspecialized inflorescence many small flowers being condensed into a conspicuous head or capitulum . Division of

labour is so well developed that a capitulum resemblesa single flower (see p . 1 55 , Fig . and the arrangementsfor pollination by insects and dispersal of the pappose fruit sby the wind

,are so perfect that the flowers represent the

highest stage of development yet reached byflowering plants .

The order is d ivided into two main groups

( 1 ) Tubuliflorae.

—P lants without milky latex and the

florets of the disk tubu lar, not strap- shaped , e . g . Daisy,Coltsfoot (see pp . 1 78

—80 ,Figs . 1 22 and and

Thistle .

(2) Liguliflorae.

— P lants with a milky latex and the

florets all strap- shaped,e . g . Dandelion (see p . 1 8 1

,

Fig . Goat ’s-beard,and Hawkweed .

Interestingmodifications aremet with in the florets Of the

same capitulum as regards distribut ion of stamens and

pistils, and the following should be studi ed

Usually the ray florets are female and the disk-florets

hermaphrodite as in the Daisy (Belli s perenni s) (see p .

Dog Daisy (Chrysanthemum Leucanthemum) , and CornMarigold (C . segetum) . In the Sunflower (Helianthus

annuus) the ray-florets are ligulate and neuter ; the

disk-florets tubular and hermaphrodite . The Cornflower

(Centaurea Cyanus) has tubular and neuter ray -florets and

tubular and hermaphrodite disk-florets . The Butter-bur

(P etasi tes vulgaris) is dioecious ; the male heads are few

flowered (about thirty) , produce honey and pollen,and

have a barren ovary and style . The female heads are larger

(abou t 1 5 0 florets) two or three of the outer ones are

male, the rest being female and producing no honey

or pollen . The Groundsel (S enecio vulgari s) has no ray

florets , is inconspicuous and self—pollinated . The Ragwort

DICOTYLEDONS : METACHLAMYDEAE 263

(S . jacobaea ) , belonging to the same genus,has conspicuous

flowers with ligu late ray -florets an d is pollinated by insects .

In a few cases the fruits are,

dispersed by animals ;e . g. the Bur Marigold (Bidens triparti ta) has hooked fruitsand in the Burdock (Arctium spp. ) the bracts end in recurvedhooks and the whole head may be dispersed .

Many Composites are cult ivated for their flowers , e . g .

Sunflower , Aster, Dahli a , Chrysanthemum ,and Cornflower .

Some are interesting Alpine plants,like the Cudweeds

(Gnaphalium spp. ) and the Edelweiss (Leontopodiumalpinum) .The young flower-heads of the true Artichoke (Cynara

S colymus) are eaten . The Jerusalem Artichoke (H clianthus

tuberosus) has underground tuberous stems with eyeslike the potato (see p .

The Metachlamydeae or Sympetalae, which containsmore than Species , shows much greater uniformityof flower- structure than does the Archi chlamydeae .

The parts of the flower are definite in number and cyclicthe corolla is usually gamopetalous and the stamensepipetalous . The ovu les have a single integument . The

more simple forms , including the Heath and Primrose, have

hypogynous flowers , the parts are in five cycles or whorls ,two of which are stamens

,and the number of the carpels is

the same as in the other whorls . In the orders to whichbelong the Li lac

,Forget -me—not , Deadnettle ,

N ightshade,and Speedwell

, the flowers are hypogynous, the parts arein four cycles

, the carpels fewer than in the other whorls .In the higher types the flower is

'

zygomorphic . The

highest stage of development is reached in the order Com

positae , the flowers of which possess the following com

binat ion of characters : the corolla is gamopetalous and

epigynous , and the anthers are syngenesious . The fru itis small , seed- like, and often provided with a pappus . The

inflorescence consists of a large number of small dimorphic

flowers condensed into a compact head .

SYSTEMATIC BOTANY

CHAPTER XX I

CLASS I I , MONOCOTYLEDONS

IN the second division of Angi osperms , namely Mono

c oty ledons , the embryo has only one cotyledon and isgenerally surrounded by endosperm . The plan ts are

usually herbaceous ; the stem has many scattered and

closed vascular bundles (i . e . there is no cambium between

the wood and the bast) , and secondary thickening is rare .

The leaves are usually parallel-veined and linear . The

parts of the flower are in threes , often in five whorls withthree parts in each whorl . Most Monocotyledons are

perenn ial herbs and many hibernate by means of rhizomes,

corms,or bulbs . Many are characteristic of regions exposed

to long, dry periods , e . g. steppes , prairies , and semidesert areas . The linear grass type of leaf is dominant ,and plants of this class cover enormous areas , as in the

grassy vegetation of temperate regions , which is a charac

teristic feature in the scenery . We are familiar wi th i t

in our pastures , meadows , and cornfields in grass moorsand cotton-grass mosses in reed swamps and the marginalvegetation of our ponds

,lakes

,and rivers .

Tree- like forms are exceptional,and are chiefly confined

to tropical regions,where they form a conspicuous feature

in the vegetation ; the most striking examples are the

Bamboos, the Dracaenas (e . g . the Dragon Tree) , Agaves ,Aloes , and Palms . Many of these have a peculiar mode of

secondary thickening .

The orders in this class includemany Species well known as

important food plants,and alsomany garden favourites, e . g.

Gramineae (Grasses , cereals) , Li liaceae (Lilies) , Amarylli

daceae (Daffodi ls) , Iridaceae (Irises) , Orchidaceae (Orchids) .


wild plants or cultivated in gardens for their showy flowers ,e . g . the Bluebell (S ci lla nutans) (Figs . 87 and

Hyacinths (Hyacinthus Tuli ps (Tulipa) , Star ofBethlehem (Orni thogalum umbellatum) , Li ly of the Valley

(Convallaria majali s) , Herb Paris (P aris quadrifolia) ,Bog Asphodel (Narthecium ossifragum) , Onion and Garlic

(Allium Solomon’

s Seal (P olygonatum ofli cinale) ,

QFritillary ,

Funkia, and the

Autumn Crocus (Colchi cumautumnale) . Some are

climbers,like the beautifu l

Gloriosa with leaf- tip tendrils , and Lapageria with

twining stems . Some are

very large : e . g . Yuccas ,Dracaenas , Aloes , and the

New Z ealand Flax (P hormium tenax) . Species of

Asparagus , Smilax, and

Butcher’

s Broom (Ruscusmany Of which are

climbers,develop peculiar ,

FIG . 1 77 . FLORAL D IAGRAM OF leaf- like stems (phylloH YAC INTH .

- br , bract .0 1ades) (Fig . 96,

Order AMARYLLIDACEAE . P lants simi lar to Liliaceae but

wi th ovary inferior . Mostly herbaceous perennials

with bu lbs or rhizomes . Inflorescence cymose , and

in bud enclosed in a spathe consisting of two fusedbracts . Flowers regu lar, somet imes zygomorphic

,

hermaphrodite perianth of six united petaloid lobes ,in two whorls of three each . Stamens six

,epipetalous

anthers introrse . Carpels three , syncarpous ; ovaryinferior, three-celled , ovules numerous , placentationaxile . Fruit a capsu le or berry (Fig . Floral

formula P A G

MONOCOTYLEDONS 267

The order is a large one ,and most of the species occur

in dry climates , tropical or sub - tropical . They hibernateduring the unfavourable season by means of their bu lbs orrhizomes . Many are cultivated for their large ,

showyflowers e . g . the Daffodi l (Narci ssus P seudo—narci ssus)with a single flower

,Jonqu i l (Narci ssus J onqui lla) with

a cymose umbel of flowers , Snowdrop (Galanthus nivali s) ,Snowflake (Leucojum) ,Ag a ve , A l s tr o emer i a ,

Amaryllis , Crinum, and

Eucharis .

Order IRIDACEAE . Per

ennial herbs , h iber

nating by means of

rhizomes,corms or

bulbs . Flowers regu

lar or zygomorphicperianth petaloid of

six lobes in twowhorlsunited to form a

tube . Stamens three .

Carpels three, syncar FIG . 1 78 . FLORAL D IAGRAM OF

pous ovary inferior , IRIS — br , bract .three-celled with indefin ite ovules style branched , often petaloid fruit

a capsu le . Floral formula P A 3 + o , G

(Fi g .

Many of the species are adapted to a life in countriessubject to considerable dry periods and many of them

occur in South Africa ,Tropical America ,

and the Medi

terranean region . They include a number of garden

favourites , e . g . Crocus (Figs . 85 and I ri s (Fig .

Ixia,Gladi olus

,F reesia

,and Tritoma . Very few occur in

Britain the most familiar are the Yellow Flag (I ri s P seud


acorus) , Foetid Iris or Gladdon (I ris foetidissima) , Crocusvernus and C . nudiflorus .

Order ORCHIDACEAE,

Orchids . Perennial herbs .Flowers hermaphrodite and i rregular . Perianthusually petalo id , of six lobes , the inner median one

generally forming a lip or labellum . Stamens reducedto one

, rarely two . Carpels three ,syncarpous ovary

inferior , one - celled placentation parietal and bearing

FIG . 1 79 . FLORAL D IAGRAM OF ORCH Is .—br , bract .

numerous minute ovules . Axis of flower prolonged asa column above the ovary, bearing the stamens andstigmas . Fruit a capsule and contains very manyminute seeds . Floral formula P A 1 + 0 or

G (a) (Fis I 79) ~

This order is a very large one , with 40 0 genera and

species eighteen genera and fifty species occur in Britai n ,many of which are rare . They are most abundant in thetropics , and differ widely in structure according to theirmode of life and habitat many occur as epiphytes on the

PART IV

COMMON TREES AND SHRUBS

CHAPTER XXI I

CONE-BEARING TREES

IN the vegetation of the earth , trees occupy the first

place . By vi rtue of their s ize,wide-spreading branches ,

and dense foliage,they exert a dominating influence on

more lowly plants growing beneath them ,and when growing

together in large numbers , as in a forest,not only give

a characteristic aspect to the scenery, but affect in no small

degree the climate of the country in which they grow .

They yi eld many products of great value to man,provide

shelter for his home and for his domestic animals,and add

much to the beauty of his surroundings . A study of plants,

therefore,is incomplete without a knowledge of trees

,and

in this section a number of the more common kinds havebeen selected for study .

Scots P ine

Scots P ine (P inus sy lvestri s) is commonly planted inBritain , S ometimes forming large plantat ions

,and fre

quently scattered amongst other t rees in woods . It is

sometimes known as the Scotch Fir . In Scotland and

Norway it forms extensive forests . The smaller trunks are

FIG . 1 8 0 . A YOUNG P INE,S HOWING BRANCHE S IN FALSE

WH ORLs .

— Each ends in a terminal bud surrounded by a fewlatera l buds .

FIG . 1 8 1 . TH E NARROW-LEAV ED WILLOW IN WINTE R .

272 COMMON TREES AND SHRUBS

Examine the old fallen needles, and determine the

structures whi ch are thrown off . It is the dwarf shootsthat fall and not merely the needle-leaves .Exami ne an old branch and note that the bases Of the

scale-leaves of the long shoots persist and harden,and so

produce the roughness of the branch .

FIG . 1 82 . S COTS P INE .— I

,dwarf sh oot ; 2 , elongated Shoo t

bearing scale -leaves with dwarf shoots in th eir axils female conenear end of branch 3 , male cone 4 , a single stami nate branch5 , pollen-

grain ; 6 , branch bearing young female cone ; 7 , ovu lebearing scale ; 8 , winged P ine-seed 9 , Old female cone a , stamens

ds,dwarf shoots ; f , foliage -leaf m

,micropyle ; o , ovu le po,

pollen-sac s .b, staminate branch so, scale-leaves w, wi ng .

The‘ flowers ’ of the pine are in cones and differ in

several important respects from typical flowers . The seeds

are not developed in the same cones as the stamens , but

arise on di fferent branches of the same tree (monoecious) .

The male cone (Fig . 1 82 , 3) arises at the end of a branch ,

and consists of a central axis which bears a tuft of dwarfshoots at the tip . Below ,

and in the axils of the scale

CONE-BEARING TREES 273

leaves , short branches arise which bear a few scales below ,

and numerous spirally—arranged stamens above Each

stamen has a very Short filament and the anther bearstwo pollen - sacs on the under surface When ripe ,

they spli t longi tudinally and the pollen -

grains escape in

immense numbers . Each pollen-

grain 5) is provided withtwo air-bladders which serve as floats

,and i t may be

carried a great distance by the wind . When the pollen isshed

,the staminate shoots fall off

,

and the dwarf shoots at the t ip

develop thei r pai rs of needles .

The female cone (2 , 6 , 9) arises

near the end of a branch and in the

position of a lateral bud . At first

i t is abou t a quarter of an inch long ,

and appears to be terminal , but later

i t is seen to be lateral It remainson the t ree three years

, growinglarger each season . The cone con

sists of a central axis on which areF IG - 1 8 3~ S EEDLING

P INE .— c , cotyledons ;

scale- leaves,and on the upper surface

f . first green need leof each scale- leaf grows a much leaves .

larger, thick , flat , woody scale ,i . e .

the carpel . On the upper surface of each carpel are two

straight ovules (orthotropous) wi th thei rmicropyles (m)point ing towards the axis . They are not enclosed in an

ovary ; there is no style and no stigma ; hence there is

no pist il as in typical flowers .

When ready for pollinat ion the axis elongates ,lift ing the

carpels apart,and between them the pollen—grains pass and

are carried directly on to the micropyle of the ovule .

Pollination occurs in May of the first year,but fertilization

does not take place until June of the second year . Whenripe the carpels become woody gape open from above

downwards , and allow the seeds to escape,each carrying

1 296 S


wi th i t a thin shaving from the carpel , which serves as

a wing for seed-dispersal (Fig . 1 82 ,

The ovule of the P ine ,unlike that of other flowering

plants,becomes filled with endosperm before fertilizat ion .

When ripe ,part of this persists around the embryo , which

has a radicle ,plumule ,

and eight needle- shaped cotyledons .

On germination the t ips of the cotyledons remain in the

seed and absorb the endosperm . The plumule elongates

and bears , for the first two years , not scale- leaves,but green

needle- leaves . Then as new ones form,they become more

scale—like ,and buds aris ing in thei r axils give rise to dwarf

shoots,each with two needle- leaves (Fig .

Lar ch

Though commonly planted in woods , the Larch (Larixeuropaea) is not a native t ree in Britain . It grows rapidlyto eighty or one hundred feet

,and as in the P ines

,the

terminal bud cont inues growth ,and for a time the tree is

conical . The leader is eventually lost,and the t ree then

develops an open crown of sparse and delicate foliage . Itsbark is fissured , scaly, and grey ,

tinged with pink,and is

early developed on the young shoots .

The tree is easily recognized by its knotted,S lender,

furrowed branches,which arise alternately and not in

whorls . Long and short shoots are formed on the longones the leaves arise s ingly , while on the thick , slow- growingshort shoots they are numerous and in tufts (Fig .

In wet seasons the dwarf shoots may elongate and formlong flexuous drooping twigs . Buds are relatively few and

are scattered on the Shoot . Notice the large number ofscale- leaves and foliage-leaves which have no buds in thei raxils . The buds stand off at right angles and are coveredwith very many brown res inous scales . Most of these falloff as the bud opens

, but the lower ones persist and harden .

The leaves are abou t an inch long and needle- like,but thin

,

flat,and soft . In early spring they are bright green in


midrib of the latter being prolonged beyond the scal e as

a narrow,curved process . The cone (Fig . 1 84, 4) is mature

in the following spring . It is smaller,more lax

,and has

thinner and more flexible scales than the P ine,and the

cones remain on the old twigs many years before breaking

Off . The seed is winged and is dispersed by the wind .

For two or three years , the seedling , unlike the parent , is

evergreen .

The P ine and Larch belong to a very ancient group of

plants,and differ in many important respects from Angio

sperms . The pollen-grains are more complex and deposi teddi rect on the micropyle of the ovule there is no ovary ,style, or st igma the embryo—sac of the ovule becomes filledwith endosperm before fertilization ; the egg

- cell is en

closed in a flask—shaped structure known as the arche

gonium, an organ characteristic of S impler plants such as

ferns and mosses . The seed is naked ,i . e . not enclosed in

an ovary , the latter character suggesting the name Gymno

sperms (Gr . gymnos naked) for the group to which the

P ine ,Larch

,and other cone-bearing trees , belong .

CHAPTER XX I I I

CATKIN-BEARING TREES

W illow

Two kinds of Willow are very generally recognized‘

the Palm and the Osier . The P alm or Goat -Willow

(S alix capraea) (Fig . 1 85 ) grows on dry banks and in woods

and hedges , is of Shrub—like habit , from fifteen to thirty

feet high ,and has short

,knotted branches loaded in early

spring with bright yellow catkins . The male flowers each

CATKIN-BEARING TREES 277

have two s tamens . The leaves , which appear later , are

broad and oval and have somewhat kidney- shaped stipules .

The Os ier (S . viminali s) is common in wet hollows , bystream and river- s ides

,and especially in low- lying

,marshy

districts , where i t is frequently coppiced ,i . e . cut close to the

ground . From both adventi tious and dormant buds on

the stool,very long

,flexible

,switch- like branches grow ,

which are used for basket -making . The catkins are long

and slender,the male flowers have two stamens

,and the

capsules are hai ry . The leaves (Fig . 78) have narrowstipules ; the blades are from four to eight inches long ,

lanceolate, pointed , and s ilky beneath .

Another species,the White Willow (S . alba) (Fig .

is common in similar S i tuations , and attains a height of

from eighty to ninety feet . It has narrow leaves , silky

white on both sides , and the male flowers have three

stamens .

Other species and varieties with quick-growing shoots

and narrow leaves , besides the Osier, are coppiced , and

pollarding is common with the larger species . In pollarding,

the large branches are cut Off several feet above the ground

and new branches , springing from dormant and adventitious

buds around the cut surfaces,form a dense crown .

Some Willows growing on sand-dunes and moors are

much smaller,being only one to three feet high (Fig .

while some alpine species are not more than one or two

inches high ,and form a flat carpet on the ground . No

other genus of British trees has such a bewi ldering number

of species , varieties , and hybrids (i . e . crosses between

the di fferent forms) , as the Willows .

The buds , often pressed against the stem ,are covered by

one scale , composed of two fused leaves . The larger flower

buds give rise to short shoots ending in a catkin (Fig . 1 85 ,

1 and and the smaller leaf—buds grow into long,leafy

shoots . The end bud , and somet imes more,of the branch


dies (Fig . and growth is then continued by the next budbelow . The flowers (Fig . 1 85 , 3 and 4) have been describedon p . 1 60 ,

and are in catkins,male and female on separate

t rees,i . e. they are d ioecious . In the Goat -Willow the cat

ki ns appear before the leaves , but in the Osiers leaves and

FIG . 1 8 5 . THE GOAT-W i LLow .

— I , leafy shoot bearing fema le

catkin ; 2,branch bearing two male catkins ; 3 , female flower

4 , male flower ; 5 , capsule d eh isc ing ; 6 , pappose seed ; 7 , flora ld iagram of female flower ; 8 ,

floral d iagram of male flower ; a,

stamens br,bract f .c, female catkin n , nectary o,

ovary

catkins are out together . The fruit is a capsule (Fig . 1 85 , 5 )opening by two recurved valves . The seeds are numerous ,and each is provided with a tuft of hairs as an aid to wind

dispersal . Fig. 1 57 is a photograph of fruiting Willows on

a sand-dune ; they have the appearance of being coated

with cotton wool .


If these are traced they will be found to spring from longroots of the parent tree which grow horizontally just below

the surface ,the main roots being deep in the soi l . Such

shoots are called suckers , and they afford a means of‘

vege

tative propagat ion . In the late summer or early autumn

the ground near Poplar trees is often strewn with leafy

FIG . 1 86 . BLACK P OPLAR .

—1,leafy shoot ; 2

,twig with

branch -scars ; 3 , male catkin ; 4 , ma le flower ; 5 , female catki n ;6 , female flower ; b.s , branch - scars ; d , cup

- like d isk ; s .s , bud

sca le scars .

shoots , varying in length from one to six feet . These are

deciduous shoots cut off by a separation - layer,as in the

leaves (Fig . 1 86,2 b.s) . Compare this wi th what occurs

in the P ine .

The flowers are in catkins and,as in the Willows

,are

dioecious , but have no nectaries and secrete no honey .

They appear before the leaves . The male catkin (3) is lax ,

pendulous,and about two inches long . The bracts are

CATKIN-BEARING TREES 28 1

f ringed , and in the axil of each is a flower cons istingof a cup

—like disk (d) , and bearing thi rty to forty stamenswith du ll red anthers . Much pollen is produced and dis

persed by the wind . The flowers of the female catkin

(5 and 6 ) are also axillary . A cup—like disk surrounds the

ovary,and the pistil consists of two united carpels . The

ovary is one- celled,and above it are two large branched

stigmas The capsules,when ripe ,

spli t by two valves

and the seeds , each bearing a tuft of hai rs at the base,are

dispersed by the wind .

Hazel

The Hazel (Corylus Avellana) (Fig . 1 87) is a shrub or

small tree from ten to fifteen feet in height,often forming

a conspicuous , shrubby undergrowth in Oak and Ash woods .

It is frequently coppiced ,and from the old s tools which

remain,shoots grow out freely

,numerous branches thus

arising Close to the ground . As in the Poplar,suckers

spring from adventitious buds on the roots . The cork arises

immediately beneath the epidermis (as in Fig . and for

several years forms a smooth shining bark,on which are

prominent transverse lenticels (Fig . 1 87 , 1 I) , but , later, thebark peels off in ring—like scales .

Branches of two kinds occur : first the main stem and

the old branches,on which the lopsided leaves are arranged

in two rows and secondly the quick-growing stool- Shoots

and suckers,on which they are in three rows and have

larger and more uniform blades . The buds are oval andcovered with bud—scales

,the nature of which may be eas ily

made out by examining an opening bud . Note the transition from the outer brown scales to scales consisting of pairsof stipules covered with silky hairs

,while the innermost

pairs have each a small blade between them . The stipulesonly remain for a short time after the bud opens

,but last

longer on the leaves of the stool—shoots and suckers . The


young shoots are zigzag and hai ry, and produce a leaf at

each angle .

The leaves (Fig . 1 87 , 2 ) are short- stalked ; the blade islarge and somewhat orbicular ,with a doubly serrate margin

and a pointed apex,and the surfaces are rough and hai ry .

In the bud the leaves are pleated , i . e . folded between the

lateral veins and then upwards along the midrib .

Buds are formed in the leaf-axils , but the terminal bud

dies . In the following year the highest lateral bud grows

FIG . 1 8 7 . HAz EL .— I

, flowering branch 2,foliage- leaf 3 , male

flower 4 , flora l d iagram o f the male c yme 5 , two female flowersin axil o f bract ; 6 , flora l d iagram of female cyme ; 7 ,

fru itingbranch ; 8 , fruit in longitud inal section ; a , anth ers of branch edstamens br , bracts c , cotyledon ; cu

, cupu le f .c , female catkin ;

l , lenticel m .c, male catkin ; p ,p lumu le ; pe, perianth ; r , rad icle ;

st, stigma .

into a long, zigzag shoot ; but those below form dwarfshoots

,some of which produce a tuft of leaves

,while others

become flower-buds . Those which will form male catkinsdo not res t during the winter

,but elongate the same year

hence we find t ightly-packed male catkins hanging on thetrees in winter (Fig . 1 87 , In mi ld weather they may

open in December, but in severe weather they may remainClosed until the end of February or the beginning of March .

Th e Hazel is monoecious . The male catkins (Fig . 1 87 , 1


Birch (Betula tomentosa) is themost abundant . Its branches

are greyish—brown ,s lender

,but seldom droop

,and the

fresh young twigs are hai ry . The S ilver Birch (Betulaalba) is a more elegant t ree and is not so common .

'

The

branches are long and slender and often droop gracefully .

Its young twigs are covered with resinous warts .

The buds are ovoid and covered with stipular scales , andthe same gradation is met with as in the Hazel . The

leaves are alternate,scattered and small the base is small

and leaves a small scar the stalk is slender and the blade

variable . Usually i t is broadly ovate to cordate,with

a doubly serrate margin,and the surface is glabrous with

prominent veins beneath .

The Birch is a tree of fresh air and sunshine . It has a

very open canopy,i ts small scattered leaves (Fig . 1 88 , 2 )

do not form mosaics,and nei ther shade each other nor cast

much shade on the ground . It grows badly under theshadow of other t rees

,and is thereforecalled a light-dem and

ing tree . Usually the undergrowth is equally light

demanding .

The male and female flowers are in separate catkins onthe same t ree (monoecious) . The male catkins are developed in the autumn

,and are seen on the trees throughout

the winter, two or three together at the ends of the twigs

(Fig . 1 88,1 m o) . In the spring , as the leaves come out , the

catkins elongate,droop

,and shed an abundance of pollen .

The flowers are arranged on the catkin in three-flowered

cymes (3 and On the upper side of each bract are two

smaller bracts (3 br) ; then three flowers,each with two

spli t stamens , which thus resemble four stamens .

The female catkins are enclosed in buds during the winter ,but in February they begin to open ( 1 f .c) . At the base

three or four leaves form on dwarf shoots,and each shoot

ends in a slender catkin . As in the male catkin the flowers

are in threes Each bract has two small scales above i t

FIG . 1 88 . BIRCH .- I

,winter Sh oot 2

,leafy shoot ; 3 , flora l

d iagram of male cyme 4 ,floral d iagram of female cyme 5 , brac ts

o f female flower ; 6 ,winged nu tlet ; br , bracts d .s , dwarf sh oo t

with foliage - leaves and fruiting catkins f .c , female catkinsm .c ,

male catkins t, d ead terminal branch .


(Fig . 1 88, 5 ) and three small flowers . Each flower cons ists of

a pistil of two carpels the ovary is two- celled,flattened

,

and bears two stigmas . There is no cup ,and only one ovule

develops . The ovary when ripe becomes a winged n'

utlet

The catkin elongates as it ripens (2 f .c) , and the

bracts with the two scales attached ,as well as the winged

frui ts,are scattered by the wind .

Alder

The Alder (Alnus glutinosa) (Fig . 1 89) is a characteristictree by stream- sides and in low- lying marshy districts

,

where,along with Willows , i t often forms a characterist ic

thicket . It is usually a small t ree,rarely more than fifty

feet high ,and

,growing from the base of the trunk , are

Often many stool-Shoots , which give i t a shrub- like appear

ance . On the roots large clusters of nodules grow ,similar

in function to those found in leguminous plants . Like

the Birch ,i t is a light -demanding - t ree

,and

,when young ,

grows rapidly and soon frees itself from the shade of its

neighbours .

The bark is brownish -black and fissured,with wide scaly

ridges . The young branches and buds are greenish -brown

to red or violet , and when seen from a distance an Alderthicket is often a rich purple . The longer quick-growingShoots are smooth but with conspicuous reddish lenticels

,

and somewhat t riangular in section on account of the

prominent decurrent leaf-bases (Fig . 1 89, 1 and 2 Lb) .The buds are rather large

,triangular

,and distinctly

stalked (b) by a slight elongation of the axis beneath thelowest bud-scale . The leaf-scars are ovate to rhomboid

,

with five leaf-traces,often reduced to three by the fusion

of the three lower ones . The bud- scales are stipules

(Fig . 1 89, coated with a waxy secretion,and are not easy

to separate . Note the relat ionship between leaves and


stipules as Shown in the diagram . On the lower part of theshoot are numerous small dormant buds .

The leaves are stalked,and the base decurrent and

stipulate . The stipules fall Off when the leaf is mature the

blade is obovate,doubly serrate

,and h as a rounded or Often

notched apex . The leaves are folded fan-wise in the bud .

The flowers are in catkins,and both male and female

occu r on the same tree . Both are developed in the summerandmay be seen on the tree before the leaves fall (Fig . 1 89,

They are thus exposed throughout the winter and openabout February in the following year

,before the leaves

appear The male catkins ( 1 and 2 m o) are long and

pendulous . On the upper surface of each bract,and united

to it,are fou r scales (5 so) , and three flowers

,each flower

having a four- lobed perianth and four stamens . The

female catkins ( 1 and 2 f .c . ) are small and erect the

bracts and scales are the same as in the male catkins,but

there are only two flowers,the central one not being de

veloped (6 andWhen fertilized the ovary becomes a dry

,flattened ,

one

seeded nutlet . Each bract with i ts four scales grows and

becomes a green five- lobed woody scale ,the whole resem

bling a small P ine cone ( 1 o) . The nutlets ripen in the

au tumn but are retained until the following springthe scales then dry and separate and allow the nutlets to

fall out,when they may be dispersed by the wind or fall

into the stream and be carried some distance before being

washed ashore . The old dead blackened cones remainseveral years on the trees before they are broken off ( 1 d) .

Note the different years ’ flowering Shoots representedon the branch in Fig . 1 89,

1 . At the growing end are the

catkins (f .c and m.c) , which will remain on the tree all

the winter,and open in the following spring . Below are the

ripe female cones (c) of the present season ,and lower st ill are

the old cones (d) , which shed thei r fruits the previous year .

FIG . 1 9 0 . BEE CH WOOD IN WINTER .


membraneous scales , which are stipules . The leaves are

folded fan-wise and covered with S ilkyhai rs (Figs . 72 , 75 ,

As the bud opens and the leaves , which are in two rows,

mature,the fringed stipules fall off . The leaf-base is small ,

and leaves a small , oval scar with three leaf-traces the

FIG . 1 9 1 . BEECH .—I

,leafy shoot showing leaf -mosaic ; 2

,

flowering shoot 3 , male flower 4 ,female flower 5 , fru it enc losed

in'

a spiny cupu le ; a , stamens ; br , bracts ; f .c ,' female catkins

m .c , male catkin pe, perianth .

stalk is Short and hairy ; the blade oval,thin

, and tough ,

smooth above and s ilky beneath the margin is wavy and ,

when young,fringed with hai rs .

In young trees and in cut Beech-hedges,the leaves turn

a light brown in the autumn and remain on the twigs all

the winter . The spreading , plate- like branches of the

CATKIN—BEARING TREES 29 1

Beech,forming tiers of mosaics facing the sky ,

produce

a closer canopy and cast a deeper shade than any other

Brit ish tree ,and the vegetation beneath is very scanty .

As regards light , i t stands at the opposite extreme to theBirch it is a shade- enduring tree .

The flowers are in heads,which arise in the axils of the

leaves of the current year,and therefore come out after

the leaves . The stamens and pistils are in separate flowers

on the same tree (Fig . 1 91 , The male flowers are ina globular cluster at the end of a long , pendulous stalk .

Each flower has a perianth of four to seven hai ry lobes

and from eight to twelve stamens . The female flowers

(4) arise higher on the branch ; the stalks are Short,

thick,and erect ; and each inflorescence contains only

two flowers . A S ingle flower consists of a three- celled

ovary with two ovules in each cell,and three red st igmas .

On the top of the ovary is a perianth with about six lobes .Surrounding the two flowers is a hairy cupule

,which

,after

fertilization,becomes thick

,woody, and spiny and

when ripe splits into fou r valves . One nut is formed ineach flower ; i t is t riangular , wi th a smooth brown coat

,

and contains only one seed .

Oak

The Oak (Fig . 1 92) is the larges t and most characteristicof British trees , and formerly Oak forests covered a largepart of England . Two species are common

, and they

sometimes characterize distinct habitats . The Sess ile Oak

(Quercus sessi liflora) is the dominant tree on Shallow ,poor

siliceous soils , and is typical of the woods on the Pennine

slopes,and other S imilar hilly regions . The Peduncled

or Stalked Oak (Q . Robur) is often the prevailing tree in

lowland woods , with a deep ri ch siliceous soi l over clays

and loams . On soils containing much lime,both species

tend to occupy a very subordinate place in the vegetation .

T 2


Often the two species grow together, then hybrids betweenthem are frequent . The Oak grows to a great age and size,and weather—beaten specimens , like the Cowthorpe Oak inYorkshire

, may have a t runk seventy feet in gi rth . The

t runk attains a height of one hundred to one hundred and

fifty feet,and is much branched . A characteristic feature

of the tree is its gnarled and contorted branches , which endin clustered twigs . The bark is rugged ,

with deep verticalfurrows ; the ridges break transversely and form oblongscales (Fig .

The buds are crowded around the ends of the twigs

(Fig . If the end bud persists,i t grows into a long

shoot,but frequently it dies and the lower buds grow out

as a cluster of Short,leafy twigs . Dwarf shoots

,though

common,are not regular, as in the Beech and the buds in

the lower leaf-axils and in the axils of the bud-scales aresmall and remain dormant (Fig. 1 94, 1 db ) . The buds are

s tout,blunt

,and oval , and are covered with about twenty

stipular scales . The twigs,with numerous small oval

lenticels,are somewhat angular on account of the prominent

leaf-cushions,and the leaf-scars have three or more groups

of leaf- traces .

The leaves are alternate (Fig . 1 94,and the small brown

stipules soon fall off . The base is curved,swollen

,and

continued as two lines down the stem ,and on either S ide of

i t is a stipu le-scar . In August and September the Separation- layer is seen distinctly across the leaf-base . The leafstalk is grooved above and longer in the Sessile than in the

S talked Oak the blade is obovate,deeply and irregularly

lobed (S inuate) , and somewhat leathery . In the Sessile Oak ,

the base of the blade is more or less tapering , and has manybranched hai rs on the under surface . In the S talked Oak ,

the base of the blade is produced into two recurved , ear- like

lobes (auricled) , and the hairs on the under surface are few

and simple .

CATKIN-BEARING TREES 293

The flowers are in male and female catkins , both on the

same tree ,and appear with the leaves in April or May

The male catkins (Fig . 1 94, 3) arise e ither in the axils of the

cu .

FIG . 1 94 . OAK .

—I , winter twi g 2 ,leafy shoot 3 , male catkins

4 ,male flower ; 5 , female flower ; 6 , vertical section o f female

flower ; 7 , d iagram of female flower ; cu , cupu le d .b, dormantbuds so, scale-scars .

lower leaves or lower on the shoot from buds of the previousyear . They are long

,pendulous

,and lax ,

with the flowers

arranged in groups on the slender axis . Each flower has

a perianth with six fringed lobes and from four to twelve


s tamens (Fig . 1 94,The female catkins arise near the end

of the twigs and bear only one to five flowers . The stalk

of the catkin is long in the S talked Oak and much shorter

in the Sessile Oak . Each flower (5 and 6 ) arises in the

axil of a bract and is surrounded by a Shallow cupule . The

pistil consists of three united carpels ; the ovary is in

ferior and three- celled with two ovules in each cell ,but the ovules are not formed until after pollination ; The

s t igmas are broad , red ,and three- lobed . Usually only one

ovule develops into a seed,though very small ones may

also be found within the polished shell of the acorn . For

the structure of the acorn see Fig . 1 43 .

A comparison of the flowers of such catkin-bearing trees

as Hazel , Birch ,Alder

,Beech

,and Oak shows that they

di ffer in several important respects from those of Willows

and Poplars . In the Willows and Poplars (Salicaceae) theflowers are dioecious

,naked

,i . e . they have no perianth

,

and hypogynous . The pistil consists of two united carpels

the ovary is one- celled with many ovules ; the frui t isa dehiscent capsule ,

and the seeds have a tuft of hairs .

In the Hazel , Birch ,and others , the flowers aremonoecious ,

and have an epigynous perianth . The pist il has two or

three united carpels the ovary is two- celled with one or

two ovul es in each cell , and the fruit is an indehiscent , one

seeded nut .

In each case the flowers are small and inconspicuous .The s tamens produce a large quanti ty of dry pollen carried

by the wind to the large branched st igmas of the femaleflowers .


bud often dies,and growth is continued by the next lower

bud (F ig . This grows into a long shoot , while thelower lateral buds form dwarf shoots as in the Beech ,

with

a similar type of leaf-mosaic (Fig . In flowering

F IG . 1 97 . LEAF-MOS AIC OF ELM .

branches the small , pointed , upper buds produce leafy shoots ,but below these are larger globular buds which produceclusters of flowers (Fig . 1 98,

The leaves are ovate to obovate and_

often lopsided the

margin is doubly serrate with a pointed apex,rough above

and velvety beneath , The leaves of the English Elm are

TREES WITH HIGHLY -DEVELOPED FLOWERS 297

FIG . 1 98 . ELM .— 1

, flowering branch ; 2, Opening leaf-buds

3 , Elm flower ; 4 , winged fruit ; 5 , stipu les .


smaller,ovate to cordate

,and nearly smooth above . The

stipules (Fig . 1 98, 2 ) fall off as the bud opens,but those

on the stool -Shoots remain for some time .

The flowers are developed in globular buds in the positionof dwarf shoots , each containing a cluster of sixteen toeighteen flowers in small cymes . They open in March or

April , before the leaves appear . Each flower,unlike the

previous types , is hermaphrodite ,i . e . stamens and pistil

are in the same floWer (Fig . 1 98, The perianth is inferiorand bell-shaped

,with five or six fringed lobes the stamens

are five or six and opposite the lobes . The pistil is superior,of two united carpels . The ovary is two- celled and flat ,

with two stigmas .

After fertilization the ovary-wall expands into a th in,

flat,veined wing surrounding the single seed . The end is

often deeply notched and the two edges overlap (Fig . 1 98 ,

The fruits (samaras) are developed in dense clusters ,the wings are green , and a tree in full fruit appears at a

distance to be in leaf . When the fruit is mature, the wing

dries,becomes grey-brown in colour, and is dispersed by

the wind . In this country the fruits of the English Elm do

not ripen thei r seeds .

Rowan

The Rowan ”

(Pyrus Aucuparia) , as is usual with wellknown plants

,bears several other popular or local names

,

such as Roan Tree, Wickens or Quicken Tree ,and Mountain

Ash, and is very conspicuous in the autumn , when covered

with its bright scarlet berries . In distribution it follows

pretty closely the Sessile Oak,but

, although abundant in

places,it never becomes the dominant tree of the wood .

It occurs mainly on siliceous soils,but especially in heath

woods in hilly districts,where it ascends far up the moor

land valleys,becoming little more than a shrub . It is

a small tree ,fifteen to thirty feet high . The older part of

30 0 COMMON TREES AND SHRUBS

The inflorescences are developed on the dwarf shoots,

and each is a much-branched flat—topped cyme , rendered

conspicuous by the massing of a large number of smallflowers . The flowers (Fig . 2 0 0 ) open in May or June .

The receptacle forms a deep cup with the five sepals , fivepetals , and about twenty stamens attached to the rim. The

pistil cons ists of two or three united carpels which are inturn united to the receptacle-cup The styles are

FIG . 2 0 0 . ROWAN .— I , flower ; 2 ,

vertical section of flower ;a , anther c, carpels k, sepal ; p , petal r , receptacle .

free , the same in number as the carpels , and the stigmasare ri pe before the stamens . The stamens are of three

different lengths the outer and longer ones stand above

the stigmas,while the innermost and shortest ones are

incurved Round the bas e of the styles is a honeysecreting ring, and the honey is partly protected by hairsprojecting from the styles .

Numerous insects visit the flowers,such as beetles , flies ,

and bees , but , i f their visits are ineffective ,self-pollinati on

takes place . After fertilization the receptacle becomes

TREES WITH HIGHLY-DEVELOPED FLOWERS 30 1

fleshy the carpels form the core enclos ing the seeds ,and

the receptacle,at first green and small

,enlarges and becomes

fleshy and bright scarlet .The fruits are small pomes and are formed in the same

way as the apple . They are dispersed by birds— thrushes ,redwings ,

and fieldfares being fond of them . The specific

name of the tree (Aucuparia) is derived from the fact thatits berries were used to entice redwings and fieldfares into

nooses of hai r suspended in the woods .

Laburnum

The Laburnum (Cy ti sus Laburnum) (Fig . so oftengrown as an ornamental t ree

,is not a nat ive of Britain

, bu t

of Central Europe ; where in Spring it covers the lower

mountain slopes in ‘ sheets of gold as does the Gorse on

the mountains of Wales and in the west of Ireland . It isa small tree

,fifteen to twenty feet in height , with lax,

often

drooping ,branches . The bark remains smooth for many

years , then becomes fissured longi tudinal ly the branchesare greenish—brown to olive

,and the young shoots are grey

green and covered with silky hai rs .

The end buds are white,s ilky,

and surrounded by several

prominent leaf-bases on which are narrow persistentstipules

,gi ving the buds a fringed appearance . The

lateral buds are rather smaller and flattened , and reston prominent leaf-bases . Many of these buds are sup

pressed or dormant , especially on the concave side of thebranch hence the lax branching . Some form prominent

densely- ringed dwarf Shoots , resembling those of the Rowan

( 1 and 3 d .s) .The leaf-scars are small and semi -lunar

,and have three

leaf—traces . The buds are covered by two or three ratherloose scales which Show transit ions to foliageleaves

,thus

proving that they are reduced leaf-bases The leaveson the long shoots are alternate and separated by


FIG . 2 0 1 . LABURNUM .-1 ,winter shoot 2

,bud - scales and young

leaves ; 3 , opening buds of leafy shoot ; 4 , flowering Shoot ; 5 ,

flower in side view ,flower - sta lk twisted 6 ,

flower in front view7 , vertical section o f flower 8 , floral d iagram a , alae d .s , dwarfshoots ; h , honey -

gu ides ; k, keel : l .b, lateral bud ; st, standard ;

s .t, stamen—trough .


planted in its place and so becomes a common woodland

tree . It also tends to spread by self- sown seedlings . InScotland i t is known as the P lane Tree

,but i t must not be

confused with the true P lane so commonly planted inLondon

,which is a form of P latanus acerifolia .

It is a large tree,fifty to sixty feet high ,

with a widespreading, somewhat pyramidal

,crown . The ash—coloured

bark is smooth,and in the Old tree scaly

,but not fissured .

The terminal bud continues growth therefore branchingis monopodial . The buds are in crossed pai rs (Fig . the

terminal and also the flowering buds being larger than thelateral buds . The branches are S laty-

grey to reddish—brown ,and are dotted with numerous lenticels . The details of

a shoot,the st ructure of a bud

,and the format ion of the

leaf-mosaic have already been described (pp . 1 1 3— 1 4,

Figs .

70 , 7 1 ,and

Beneath a Sycamore on the side of a road the pavementis often covered with Shining rain- like drops

,due to a sticky ,

sugary excretion called honey-dew from aphides which

infest the leaves . They suck the sap and exude drops of

honey-dew,which spread over the leaves like a varnish .

When the aphides are abundant, the drops fall from the

tree like fine rain .

Two opposite buds are formed immediately below the

terminal one ,and i f the latter produces a flowering shoot

the axis ceases to grow in length . The flowering shoot is

eventually thrown off and leaves a scar between the two

lateral buds , which in t ime give rise to a forked branch

(fal se dichotomy) .The flowers arise in large end buds: The inflorescence

(Fig . 2 0 2 ,1 ) is a pendant raceme of umbel- like cymes

,each

with three or four flowers opening in May or June . The

flowers vary in the raceme . Usually.

the terminal one o f

a cyme (2 ) is complete ,and consists of five sepals and

five petals all s imilar, greenish-yellow

,and free . There

FIG . 2 0 2 . S Y CAMORE .— I

,flowering branch ; 2

,h ermaph rod ite

flower 3 , male flower ; 4 , pistil ; 5 , double samara ; 6 , verticalsection of seed sh owing th e folded cotyledons ; a , anth er ; c ,

co tyledon ; d , d isk f , funicle ; p,plumu le ; r , rad ic le ; so, scale

scars st, stigmas ; t, testa .


are eight stamens together with a pisti l which is superior,

and consists of two,sometimes three

,united carpels .

The ovary is two - celled,each cell having two ovules

, but

only one develops into a seed . The lateral flowers are oftenstaminate

,and the pistil , when present , is small and abortive

(Fig . 2 0 2 ,In the complete flowers the stamens ripen

before the stigmas .

Honey is secreted on the prominent disk at the base of

the pistil (4 d) , and ,being exposed

,is accessible to short

tongued insects like flies , which freely vi sit the flowers .

The frui t or key (see p . 2 1 4) is a double samaraand when ripe

,splits into two half- fruits . They fall

spirally and the wing aids in wind-dispersal,but

,except in

high winds , they are not carried far from the parent tree .

Horse—Chestnut

The Horse-Chestnut (Aesculus H ippocastanum) (Figs . 66,

68,69,

and 1 0 3) is a native of Greece and Asia,where its

seeds are ground and mixed as amedicine with horses ’ foodhence i ts specific name

,and the English equivalent Horse

Chestnut Another explanation of the name is that

horse or coarse is applied to it to distinguish it fromthe edible Chestnut (Castanea) . It is commonly plantedin Britain as an ornamental t ree . It grows seventy to

eighty feet high ,with an erect trunk

,three to four feet thick

at the base ,and with a broad pyramidal crown . The bark

is smooth for many years , and then becomes grooved and

scaly . As in the Sycamore , branching is monopodial,and

i n the young t rees very regu lar, with a tendency for theinner branches to be smaller . The branches curve down

wards and ou twards , and in open s ituat ions the end twigs

are markedly uptu rned and end in very large ,s ticky

,red

brown buds , the structure of which has already beenstudied (pp . 1 0 8


somet imes there are only four) , seven stamens , and a superior

pistil of three uni ted carpels . The ovary is three- celled ,wi th two ovules in each ,

and above is a single long style .

At the bases of the young petals are yellow spots whichlater turn red . The anthers and pollen are also red .

The flowers are visited by bees and are well adapted to

the s ize and habits of the humble-bee . The upper flowers

with an abortive ovary,open first (Fig . 2 0 3 ,

Later,the perfect flowers open ,

the s tyle pro jecting horizontally ,

and the stigma is ripe before the stamens,which

,at this

stage,hang downwards out of the way Thus pollen

may be carried by bees from the male flowers to the

stigmas of the perfect flowers . Finally, the stamens turn

upwards,parallel to the s tyle

,and shed thei r pollen

,and

so may effect self-pollination The bee presses its

legs between the petals , and pushes its proboscis into theflower to obtain honey from the disk on the outside of thestamens . In doing so , thehinder part of its body touches

the stigma and also the ripe anthers,and at the same time

i t carries away pollen on the bases of its middle and hindlegs . The frui t is formed from the ovary and becomes alarge and Spiny capsule . When ripe it splits into threevalves , each containing two large brown seeds .

Common Ash

The Common Ash (F raxinus excelsior) (Fig . 2 0 4) is a

native t ree , widely distributed in Britain in very di fferent

habi tats . It is especially characteristic of the woods ofthe rocky and scree- covered limestone hills in the northand wes t of England , in which i t is usually the dominant

tree . In non- calcareous areas i t is common in the wetsoils along stream-sides and is frequent in the wet carrwoods of lowland and fen districts .

’ It is sometimes coppiced . The t ree attains a height of eighty to a hundred

TREES WITH HIGHLY -DEVELOPED FLOWERS 30 9

feet,and the trunk extends almos t to the top of the oval

pyramidal , but loose ,crown . The bark (F ig . 1 96) has the

form of a meshwork of oval longitudinal fissures . Shootsoften spring from dormant buds on the trunk . The branches

arise in crossed pairs and are greenish—grey to olive—green .

FIG . 2 0 4 . COMMON ASH .- I

,Winter twig ; 2

,leafy sh oot ; 3 ,

flowering shoot ; 4 , male flower ; 5 , h ermaphr od ite flower ; 6 ,

young fru iting branch 7 , flora l d iagram o f h ermaphrod ite flower ;db, dormant buds l .s , leaf—scar so, scale -scar.

They remain smooth for a long time then become finelyfissured and have a few scattered

,longitudinal lenticels .

The twigs (Fig . 2 0 4,1 ) are thick ,

smooth,often upturned

at the ends , and sometimes form false whorls . Dwarf

shoots are common and very knotted . The terminal buds,

3 1 0 COMMON TREES AND SHRUBS

which are the largest , are short , and covered with velvetyblack hairs . Though sometimes separated by a shortinternode ,

the lateral buds are generally opposite and incrossed pairs . A flattened appearance is given to the nodes

by the large leaf-bases in which the buds are partly embedded .

The leaf-scars are large and shield—shaped,with many

somewhat fused leaf-traces . The bud-scales are in crossed

pairs ; two to four may be seen on the outside ,and

,as

in the Horse-Chestnut and Sycamore, they are leaf-bases .The leaves , which appear late

,are in crossed pai rs

,but

sometimes they are alternate (Fig . 20 4, The base is

large and has no stipules the petiole andmidrib are grooved

above,especially opposite to the leaflets hairs occur in

the groove, and sometimes small insects inhabit it . The

blade is large , compound pinnate ,and with from seven to

thirteen leaflets , which are ovate ,lanceolate

,and i rregularly

serrate ; the apex is long and pointed (acuminate) . Inyoung trees

,during damp weather

,drops of water exude

from water-pores at the leaf- t ips . When the leaves fal l,

a separation- layer forms across the bases of the leaflets aswell as across the leaf—base . This occurs also in the HorseChestnut .

The Ash ,like the Birch , is a light-demanding tree and

endures shade badly . When planted along with,and under

the shade of,quicker- growing P ines

,the young main

shoot grows rapidly towards the light and so forms a tall,

slender trunk ; hence P ines , in such circumstances , are

called Nurses by foresters .

The flowers appear in April or May and before the leaves .The inflorescences (Fig . 2 0 4 , 3) are dense ,

racemose cymes of

a dark purple colour, due to the purple-brown anthers

and stigmas . The flowers (4 and 5 ) are polygamous,i . e .

staminate,pistillate

,and hermaphrodite flowers may

occur on the same tree ,and sometimes the trees are

dioecious . The male flowers have no perianth , and consist

COMMON TREES AND SHRUBS

Many variations in bud- suppression will be found by

careful examination of a Lilac shrub (Fig . 2 0 5 , 1 to 5)

(I ) The lowest two or three pairs of buds on a shoot are

very small , and usually remain dormant (db) the

FIG . 2 0 5 . L ILAC .— I , winter shoot : terminal buds suppressed ,

lateral buds vigorous 2, forked branch formed from lateral bud s ,

between whi ch are th e remains o f an inflorescence ; 3 , branch withpersistent terminal buds , th e two lateral buds dormant 4 , terminalflower -bud 5 , dwarf shoot 6 , young leafy sh oot, showmg transition from scale -leaves to foliage - leaves ; 7 ,

flower ; 8,vertical

section of flower ; 9 ,inflorescence of P rivet 1 0

,part of inflorescence

sh owing flowers in sma ll cymes ; a , anth er ; db, dormant bud ;ds , dwarf shoot ; f .b, flow er—bud i , remains Of inflorescence ;ov, ovary ; s , bud - scales ; so, scale-scars ; st, stigma ; s . i , suppressedterminal bud .

terminal bud often dies and growth is continued by the

next pair below ( 1 s . l) (3) the terminal bud may persist ,and suppress ion occur in one or both of the next budsbelow ( 3 (4) often one of a pair lower down isdormant ( 5 db) ; (5 ) occasionally buds grow very slowlyand form dwarf shoots ( 2 and 5 db) .

TREES WITH HIGHLY -DEVELOPED FLOWERS 3 1 3

A comparison should be made of shrubs showing different

degrees of bud- suppression , and i t Should be determined

what effect this has on their form also how cutting a shrub

induces dormant buds to become active .

The buds are large and slightly sunk in the prominentleaf-bases . They are covered by four or five pairs of green

scales which are strongly keeled and , being in crossed pairs ,render the bud of a square shape in cross-section . The

scales are reduced leaves (leaf-bases) the foliageleaves

wi thin are in ten to twelve crossed pairs , and their blades

are not folded , but lie edge to edge . Below each bud is

a small,crescent-Shaped leaf- scar, with one long leaf

trace represent ing several fused veins . The leaf- cushion is

prominent and is continued as two ridges through the

length of the internode ,the posit ion of the ridges changing

with each node . The leaves have no stipules the stalk

is long, and the blade cordate to ovate ; the margin isentire, ending in a long point (acuminate) , and the surfaceis smooth (Fig . 2 0 5 ,

The inflorescence is a large,erect

,loose panicle of small ,

but showy, flowers , s imilar to those of the P rivet (Fig . 2 0 5 ,

9 and To) . The small calyx has four united sepals the

four lilac to purple petals are united into a long narrowtube with four limbs spreading crosswise

,and on the

corolla- tube are two short- stalked stamens (7 and

The pistil is superior and consists of two united carpels ,and the s tyle is divided above into two stigmas whichstand just below the anthers . The last named nearlyfill the entrance to the tube and protect the honey

,

which is secreted by the ovary and rises somewhat inthe tube .

Honey, scent , and colour attract numerous insects,the

long tube favouring the long- tongued species . If their

visits are not effect ive,pollen may fal l on to the stigma

,

and bring about self-pollinat ion .

3 1 4 COMMON TREES AND SHRUBS

The fruit is a two-valved capsule,each capsule containing

about four seeds , with a slight membraneous wing .

Both Privet and Common Ash belong to the same

natural order (Oleaceae) as the Lilac . The Common Ash

has no perianth ,though other species of Ash have

,and so

approach more closely to the Lilac . The P rivet flower

(Fig . 2 0 5 ,1 0 ) is very similar to the Lilac , and they should

be compared .

FIG . 2 0 6 . VE GE TATION OF LAKE,WOOD

,MOOR , AND MOUNTAIN .

FIG . 2 0 7 . MUS TARD SE EDLINGS IN D IFFE RENT K INDS OF SOIL .

1, surface soil 2

, sand 3 ,c layey subsoil ; 4 , clay .

PART V

ECOLOGY

CHAPTER XXV

PLANT HABITATS AND COMMUNITIES

Vegetati on of the valley and mountain — In a walk from

the bottom of a valley to the top of a mountai n manystriking changes in the vegetation are met with (Fig .

Below is the river , with ,perhaps , here and there, ponds or

lakes bordered with reeds , rushes , and other moisture~

lovi ng plants , and trees such as Alders and Willows . The

flat ground beyond ,composed of alluvium laid down in

the pas t by the river, is highly cult ivated and occupied

by cornfields and meadows , bounded by hedgerows , with

occasional undrai ned patches of marsh . On the rising

ground these meadows gradual ly give place to pas ture and

woodland or uncultivated heath ; stone walls often

replace the hedgerows and ,as we ascend , the plants vary

in character according to soils , drainage, water- supply,aspect , altitude, and the like . Higher s t ill , the trees disappear and give place to wild , bleak moorland

,perhaps

covered with deep,wet

,acid peat (Fig . 2 0 9) while the

rocky peaks forming the summits are covered with a vege

f atiou very unlike that met with at lower levels . On such

high peaks the plants are exposed to great extremes of

climate , heat and cold , wet and drought , bright sunshine,and dense, wet mist , driving and often drying winds

, and

3 1 8 ECOLOGY

influence of a series of factors,topography

,soil

,and climate

,

which will permit or favour the growth of certain species

to the exclusion o f others,and such vegetation will have

a definite character . In other words,the nature -of the

habitat must determine largely , not only the form ,but the

kind of plant growing in it . The study of plants in relation

to their habitats is called ecology (from Gr . oikos=house

or habitat) .Influence of water- supply on plant form — SO important

is the water-supply to plants that,in proportion as the

amount available is large or small,they often develop

forms_

and structures suited to the conditions of suchhabitats . In extreme cases this is so marked that special

names have been used to designate them . For example,

plants whose structural peculiarities enable them to growin water are known as aquatic plants or hydrophy tes(Gr . hydor water, phy te plant) . P lants growing inmarshy ground , as on the s ides of ponds

,ditches , and

rivers,or in wet hollows in woods

,are called hygrophy tes

(Gr . hygros moist) . At the other extreme are plants

adapted to life in habitats with an uncertain water- supply

and under conditions favouring strong transpiration , e . g .

sand-dunes (Fig . moors,and deserts . Such plants are

called xerophy tes (Gr . xeros dry) , while plants growingin a salt—marsh are known as halophy tes (Gr . hals salt) .Every gradation , however , is found between hydrophytes

and xerophyt es , and i t is impossible to draw a sharp linebetween them

,but i t has been found convenient to speak

of plants adapted to habitats intermedi ate between the

two extremes as mesophy tes (Gr . mesos intermediate) .Included under the name mesophytes are plants veryvaried in habi t

,form ,

and structure . Those which Show

marked seasonal differences , e . g . plants with deciduousleaves , which are mesophytes in summer and xerophytes

in winter,are called tropophy tes (Gr . tropos change) .

320 ECOLOGY

illustration is the society of Soft Grass,Bracken

,and Blue

bell so common in the Sessile Oak wood associations .The more important plant -associations indicated should

,

wherever possible,be studied in the field but much may

be learnt from a detailed study of those types of vegetation

which lie close at hand, e . g . the plants of a hedge and ditch ,a meadow, a wooded escarpment , or a bit of moorland .

AS a preliminary to the study of plant-associations We wi llmake a few observations on soils .

CHAPTER XXV I

THE SOIL

Origin of soi ls . S edentary and transported soi ls — If we

examine a section of soil in a quarry, as in Fig . 2 1 2 ,we can

form some idea of its origin . At the surface is a dark layer

containing the roots of the plants forming the surface vegetation . Below this is a lighter layer, the subsoil , which

grades Off into the hard rock beneath . Acted upon by theatmosphere, rain , and frost , the upper parts of the rock havebeen broken into fragments , the smallest particles beingnearest the surface and forming the soil . Such a soil hasbeen derived from the rocks below ,

and i ts surface layer hasbeen darkened by organic matter, chiefly the decayingremains of plants , which have grown in it . A soil of this

kind is said to be sedentary .

A section along a river bank is very different . Often down

to a considerable depth we find no trace of rock from whichthe soil could have been formed . The soil is made up ofparticles varying in S ize from fine grains Of sand to pebblesand even boulders , all more or less rounded and water

FIG . 2 1 2 . SE CTION OF SOIL IN A QUARRY .

FIG . 2 1 3 . SO IL ON GLAC IAL DRIFT .

322 ECOLOGY

therefore ,for vigorous plant-growth ,

must contain these

necessary constituents , and i t is from plant - remains in the

soil that much of this food is derived ; hence the greaterfertility of the surface soil . But surface soils vary consider

ably both in physical properties and ' chemical consti tution ,

according to the proportions of sand , clay , lime, humus , or

organic matter they contain .

Samples of di fferent soils should be obtained and the

properties of the different constituents studied . By meansof a few simple experiments many important facts may be

discovered .

Take a little garden -soil and weigh out I O grammes .

Spread it out to dry for a few days at the temperature of

the room,and weigh again .

1 How much has been lost in

drying ? Now place the soil on a tin lid ,heat i t for a short

time at 1 0 0°

C ., and weigh again . Has more been lost ?

Final ly,burn the soil and weigh again . How much has

been lost by burningThe part that burns away is organic matter, chiefly de

caying remains of plants . Note the change in colour afterburning ; the dark soil has become terra cotta Ten

grammes of garden soil when air—dried lost 2 5 6 grammes

of water, and a further 0 3 3 when heated to 1 0 0°C. ,

and

lost 0 -88 of organic matter on burning . What is the proportion of water to the humus in the soil ? Determinethis proportion in different soils .

Put some garden -soil into a jar of water and stir

thoroughly . Note the floating fragments of humus . Pouroff the muddy water into a large vessel and repeat thewashing until the water c lears qu ickly . Allow the muddy

water in the large vessel to stand for a few days and noticehow long i t takes to settle . Pour off the clear water and

1 Th e water—content will vary even in th e same soil,being greater

pn a wet than on a fine day .

THE SOIL 323

compare the two . The material left after washing consists

of stones, grit , and sand .

Or put a li ttle soil into a tube ,add water , and shake .

Allow it to settle and note how the layers arrange themselves . The coarsest are at the bottom , succeeded by

layers of finer and finer materials,the water above holding

the finest particles for days in suspension , while floating on

the surface will be numerous fragments of decaying leavesand stems . The part which settles slowly from the muddywater is very fine and sticky like clay, but dark- colouredwith the organic matter . Spread a layer of this on a tin lid

and bake it see what happens . It shrinks and cracks just

as clayey ground does in hot dry weather . Now add water

to i t . Does it regain its original properties Baking has

destroyed its adhesiveness .

Take three glass slips , place on each a drop of water , then

a little sand , loam ,and clay respectively, and cover with

cover-glasses . Examine them under the microscope and

note the sizes ,forms , and appearances of the particles .

Examine humus and peat in the same way ,and look for

fragments of tissues , e . g . fibres and vessels . Can you find

any threads of mou ld on the decaying parts of plantsDark garden - soil consists of small stones

,grit

,sand ,

clay ,organic matter

,and water . It differs strikingly from sub

soil in containing much organic matter , and when this is

present plants grow well in it . It seems likely,therefore ,

that from this plants get much of their food .

But before the organic matter is of use it has to be decomposed and converted into soluble inorganic salts

,as

plants can only take up their food-materials in solution .

Hence a fertile soi l must contain organicmatter, must haveth e means of decomposing it

,and must possess a suitable

water-supply to dissolve the salts when formed .

Organi sms in the soi l and their work— What are the agents

in the soil which act upon the organic matter ? Can we

x z

324 ECOLOGY

isolate them from the soil , or induce them to grow on an

artificial food-substance , so that we may examine themThe following experiment enables us to do thisSterilize some water by boiling , cover i t to keep out dust ,

and allow it to cool . Thoroughly clean and sterilize ,by

boiling ,seven test tubes and three small dishes (Petri dishes

are themost convenient) , invert them to drain off the water ,and close each tube with a plug of clean cotton wool .Label the tubes A to G and the dishes I ,

2,and 3 . Boil

a leaf of gelatine in a little water , and with this half-fill tubesA

,B , and C . Pour A into dish No . I and cover . Take a

l i ttle garden soil , sterilize part of it by baking,leaving the

rest untreated . Half-fill tubes D and E wi th sterilizedwater and to D add a li ttle baked soi l and shake up . With

a sterilized pipette transfer a few drops of the muddy liquidfrom tube D to E to dilu te i t . Pour several drops of thisinto the gelatine in tube B ,

mix them,pour into dish No . 2 ,

and cover as before .

Using the remaining tubes , repeat this with the ordinary

unbaked soil and pour the mixture of gelatine and dilutedsoil-water into dishNo . 3 . Cover and set all three aside in

the dark for a day . Look at them occasionally and com

pare the results . How do you account for the differences

If the experiment has been carried out carefully, Nos . I

and 2 remain unchanged ,but in No . 3 a number of specks

appear on the gelatine, which soon increase in size , and form

distinct patches or colonies . If a little of one of these beexamined under the microscope ,

myriads of tiny rods or

bacteria will be seenmoving in the liquid . These,together

with the moulds , are the living beings of the soi l which

decompose the organic matter , and prepare an importantpart of the mineral food which green plants take up in

solut ion . Cu lture No . I shows they were not present in theboiled gelatine , and No . 2 shows that the bacteria in thispart of the soil were killed by baking .

326 ECOLOGY

in being able to assimilate carbon dioxide in darkness . To

carry on thei r work , they not only need suitable mineralfood

,but also free oxygen and moisture . Their action is

s topped by too dry a soil and by strong sunlight . Fromthis we see why aeration of the soil is essential , and whyover-watering , which drives out the air , is injurious .

An exception to the rule as to the source of nitrogen for

green plants is found in members of the P ea family (Leguminosae) and a few others , such as the Alder and Sea Buck

thorn . On the roots of these plants , tubercles are formed

(Fig . 256 , 3 tn) as a resu lt of attacks by bacteria- like organismsin the soil , which enter by the root—hairs and cause theswellings . These organisms fill the tissues of the nodulesand are able to take up the free ni trogen of the air and convert this into nitrogenous compounds , which in turn are

passed on to the‘ host —plant as food

,or given up to the

soil when the plants decay . By vi rtue of this alliance , the

nodule-bearing plants are able to thrive in soils deficient in

nitrates . Such a union of organisms is called symbiosis (seep . If soil

,deprived of nitrates by previous crops , is

sown with Clover or other leguminous plants , and the latter

ploughed in as green manure,the loss is made good and the

land becomes richer . Another except ion is found in insec

tivorous plants,whi ch are able to supplement thei r supply

of nit rogen from animals which they capture and digest

in peculiarly modified leaves (see p .

Test for Ni trates — D issolve a lit tle potassium nitrate in

water, add three or four drops of diphenylamine sulphate,and then a little strong sulphuric acid . The deep blue

colour produced indicates the presence of nitrates . Test

a sample o f garden soil for nit rates . First dry the soil ,plug the tube of a funnel with cotton wool

,fil ter paper

,or

asbestos , and fill up with the dry soil . Carefully pourwater on i t

,and collect a small quanti ty of the water which

d rops from the end of the funnel , and test for nitrates asbefore .

THE SOIL 327

Soils vary greatly in different localities ; some are siliceous ,and contain varying proportions of grit , sand , and clay .

Others are calcareous , and contain varyi ng proportions of

1 10 AM 1 7 llOAM. 17

5 0mm 16

10 25 CAM

1 1 AM

1 .2 3. 4. 5 .

F IG . 2 1 4 . ABS ORP TION OF WATER BY D IFFE RENT SOILS .

I , sand 2,c lay 3 , surface soil 4 , subso il ; 5 , bracken peat .

lime . There are also great differences in the proportion of

organic matter present,and the amount Of water they hold .

These differences are more or less reflected on the vegetation

they support . The plants growing on siliceous soils are

often different from those on calcareous soils , and give a

328 ECOLOGY

distinct as pect to the country . S till there is much over

lapping, and very few plants occur which are unable to

exis t in either kind Of soil . The vegetation on deep,wet

2 4 5 6 7 8 9 10 1 1 12 1 5 14— '

DAYS

FIG. 2 1 5 . CURVES S HOWING THE D IFFERENT RATES AT WH ICH

WATER AS CENDS IN D IFFERENT SOILS .

peat di ffers from both this soil is more exclusive ,many

species being unable to subsist on it .

P roperties of soi ls — Different kinds of soil should be collected and thei r properties compared ,

e . g . sand , loam, clay,

lime or chalk soil , humus from a wood , and peat . Take

samples of each ,dry them, and put them into separate tubes ,

330 ECOLOGY

of humus affect (I ) the height to which the water risesand (2 ) the water-holding capacity of the soi l Continuethe reco rds for several days and plot the results in curvesas in Fig . 2 1 5 . Notice how very S lowly water ascends indry peat in Spite o f the latter’s great capacity for water .A similar experiment with dry cotton—grass peat will

show that water may rise in the column only 5—5 inches inthirty—nine days . The diagram

,Fig . 2 1 6 ,

shows the

amount of water absorbed by the different kinds of soil inthis experiment .

Half-fil l another set of tubes with similar soils, but in these

cases add 5 0 c c . of water from above . Note and mark atshort intervals the rates Of percolat ion (Fig . 2 1 7) of (I ) finesand ,

and (2 ) fine sand mixed with humus . Collect thewater that escapes at the lower end of the tubes and noticein each case (I ) rate of percolat ion

, (2 ) time of appearanceof the first drop of water from the bottom of the tube ,

(3) amount of water which escapes in a given time, (4)

amount o f water held by the soil , Observing agai n theeffect of humus on the water—content of a soil . Note that

sand is made more coherent and less pervious when mixed

with humus . If we consider these experiments and

Observat ions in connexion with our previous ones , weare able to understand why dark soi l is better for plantsthan subsoil .Make S imilar Observat ions on cotton-grass peat . Note

that it is greasy to the touch . Test samples with litmuspaper and determine whether i t is acid ,

alkaline ,or neutral .

How do peat and humus compare in these respects Peatis acid

,humus is neutral or alkaline .

Weigh out I O grammes of fresh bracken peat , dry i t , and

determine the water—content then burn it and weigh again .

How much is lost by burning ? Ten grammes of bracken

peat contained 662 water, 1 7 4 organic matter , and

1 64 mineral matter .

THE SOIL 33 1

Peat,like clay

,holds much water it is therefore badly

aerated,and root - respiration is difficult . Further, It con

tains little m ineral food and a great excess of organic

matter ; and in addition i t is acid or sour . NO wonder ,then , that i t is a poor soil for plants

,or that so few species

grow on i t .

Calcareous soils — Chalk and Limestone soils . In a

soil derived from chalk or limestone,carbonate of lime is

always present . These S oils support a vegetation differingin many respects from that growing on soils deficient inlime . The presence of lime in soils may be determined as

follows

Take 5 grammes of chalk soil , boil it in water, and pourOff the liquid . Repeat this two or three times and S O

remove the soluble calcium salts (sulphate , chloride , and

nitrate) . Drain off the water or press between fil ter paper ,and to the residue add dilute hydrochloric acid (I in I O

parts of water) . Note if there is any effervescence if so ,

i t denotes the presence Of a carbonate , e . g . of magnesium ,

lime ,or i ron . If the gas is copious i t may be led into lime

water and tested . What gas will i t beFilter Off the insoluble matter and add ammonium

hydrate in S light excess to the fil trate . Filter Off any precipitate which may result (e . g . i ron or alumina) and add

ammonium oxalate . IS a whi te precipitate formed ?

If SO, it is calcium oxalate . Thus it is shown , not only thatthe soil contai ns a carbonate

,but which specific one i t is ,

namely,calcium carbonate .

Rain -water carries with it into the soil carbon dioxide ,

which has acid properties,and which ,

act ing on the calcium

carbonate,dissolves it , S O that a soil over limestone may

become relat ively poor in lime ,except for fragments of lime

s tone rock in the soil . This denudat ion of mineral saltsfrom a so il

,and i ts consequent impoverishment , is called

leaching

332 ECOLOGY

Efleet of timing clay soi ls .

-The liming of soils, especially

in clayey districts,is common . Why is this done Clayey

soils hold much water, and are therefore badly aerated,and

organic acids formed from the decay of plants tend to

accumulate and make the soil sou r The addition of

lime lessens these defects . Two very S imple experimentswill Show us the effect of lime on clay

(1 ) Sti r up a little clay in water the very fine particles

remain indefinitely in suspension . Add to the muddy

liquid a li ttle lime-water and note i ts effect . The particles

run together in fluffy - looking masses and soon S ink to thebottom

,leaving the liquid clear .

(2 ) Bend two p ieces of gauze each into the shape of a

saucer or shallow cup and line them with wet’

clay . Pourlime-water into one and tap

-water into the other,and place

each on the top of a tumbler . Does the clay hold bothliquids equally well ? The tap

-water does not percolate ,

but the lime-water permeates the clay readily and changesits properties . It becomes less sticky it has clotted and

become more porous,and it is no longer able to hold water .

Other sal ts and mineral acids have a similar effect,and as

lime also neu tralizes the organic acids in a sour soil, we see

that i ts effects are threefold it renders the sti ff,unwork

able clay more workable,improves i ts drainage ,

and,as the

farmer says , sweetens it by neu tral izing the organic acids .

Clay is also rendered more pervious by mixing with humus .

S tate of the water in the soi l : cap i llarity .

— HOW waterascends in the soil . P revious experiments have shown

that water ascends higher in loam than in sand , and

higher s till in clay . Microscopic examination shows that ,of the three

,sand consists of the coarsest particles , clay the

finest,wh ile loam is intermediate . The larger the grains ,

the greater will be the spaces between them . Will thisin any way affect the power of a soi l to absorb water, and

if so,how

334 ECOLOGY

In the case of t rees with a wide—spreading root -systemand very large leaf—surface ,

the amount Of water drawnfrom the soil and given up to the atmosphere as vapou r is

enormous , and has an important effect in drying the

soi l and in increasing the humidity of the air . It is est i

mated that,during one season ,

a Beech wood gives Off

354 tons of water per acre,and that su itable trees planted

in marshy ground play an important part in draining i t

and bringing i t ultimately into a state sui table for higher

cultivation .

If them ineral salts needed by plants are in weak solutions,

how is it that after heavy rains the soluble compounds and

even added manures are not washed out Of the soil ? TO

some extent this does occur , as may be determined bynoting the d ifference of residue after evaporat ing (a) rainwater

,and (b) spring—water . We have seen (p . 326) how very

soluble are the nitrates in the soil and how easily they are

washed out . But chemical changes are constantly going

on in the soil , which counteract this tendency to depletion

Of food-materials . Bymeans of these changes soluble compounds like salts of potassium

,magnesium

,calcium

, or

ammonia displace the alkali in the silicates of the Soil andinsoluble compounds are formed

,and for a t ime fixed in the

soil . The next changes result in these insoluble compoundsbeing slowly acted upon and re-converted into soluble sub

s tances which provide a steady supply Of mineral food forplants .

In this manner the S oil is constantly storing up plant- food

in an insoluble form,preventing its escape ,

and then givingi t up slowly to the plants in a soluble form . It is important

,however

,that the solutions should be very weak , for

i f they exceed a concentration of 3 the plants are unable

to absorb them .

Effect o f hoeing .

— Hoeing produces a loose ,dry

,well

aerated layer of soil which conducts heat badly and pro

THE SOIL 335

tects the soil below . At the same time it reduces evaporation

,so that a hoed soil is cool and moist and therefore

better adapted to plant- requi rements . When the groundis covered with vegetat ion this receives the sun

’s heat , the

soil is screened ,and i ts temperature does not rise so much

as that of bare soil .F actors afiecting the water -supply in the soi l .— From our

previous Observations we have seen that any factor whichtends to modify the water-supply of a plant will affect itsgrowth . The more important factors are

I . Temperature. A high temperature favours rapid trans

piration ,a low temperature renders root-absorption

difficult . Much more heat is absorbed by a dark

soil than a light soil . Water is a bad conductor ofheat

,and a wet soil is a cold soil .

2 . Air is important to plants in several ways

(I ) Its temperature determines the rate of absorption .

(2 ) The amount Of mo isture present determines therate of transpiration .

(3) The oxygen of the air is necessary for respiration

both by roots and shoots,and aerat ion of the

soil is essential .

(4) Carbon dioxide is necessary for photosynthesis by

green plants .

3 . Wind . Moving air , by increas ing the volume affectinga given surface

,increases evaporation ; hence the

drying effect of winds . The rate of t ranspi ration is

great in plants having large thin leaves with sto

mata on both surfaces , while i t is reduced to a

minimum in plants with small rolled leaves wi th

stomata only on the enclosed surface, and therefore

in a still air chamber.

4 . P recip i tati on . As plants must Obtain thei r mineral

food in a weak solution,water is essent ial as a solvent

336 ECOLOGY

and diluent . It is obvious , therefore ,that a suitable

water-supply is the most important edaphic or soilfactor . Water carries into the soil gases from the

air,one of which , carbon dioxide , gi ves to water

the power Of dissolving part Of the mineral matterof the soil , e . g . potash and lime . On the physicalcharacter Of the soil depends the amount of wateravailable for plants . The rainfall of a distric t willplay an important part in determining the character

of the vegetation .

We general ly find that plants growing in a sour, wet ,

cold soil have peculiarly modified shoots . The leaves are

reduced,and either up- rolled or back-rolled the cuticle is

thick the stomata are sunk in grooves or pits and similar

devices occur which serve to reduce transpiration . P lantsgrowing in a wet so il may possess structu res characteristic

Of those found in habitats liable to periods of drought . If

the soil , though it contains much water, is too acid,too

cold,or if the water is otherwise rendered difficult to absorb ,

i t is said to be physiologically dry

CHAPTER XXV I I

PLANTS OF HEDGEROWS AND WALLS

Uses and di stri buti on of hedgerows .

—Hedgerows provideend less material for the study of plants and Offer numerousproblems for solution . They are , however , fences introduced by man and not a natural feature of the vegetation

of a country . Hedges are u sefu l in many ways . Theyprotect the crops and surface soi l from the drying and tear

338 ECOLOGY

PLANTS OF HEDGEROWS AND WALLS 339

climbing organs also those with fruits dispersed by

animals , especially birds .

Examine such a hedgerow and draw to scale a transect

passing through the above-mentioned zones and indicateon it the Species met with , as in Fig . 2 1 8 .

Make lists of the species found in each zone and carefully

compare the different forms .

Study the changes that occur throughout the year, e . g

Winter .

— The deciduous and evergreen habits ; branchsystems ; bark of trees winter-buds ; protection ;leaf- scars .

Spring — Nature of bud- scales ; opening buds ; folding

of leaves and their modes Of growth ; spring t intscharacteristics of spring flowers wind-pollinationplants with storage organs, tuberous roots, rhizomes ,bulbs .

Snmmer .

— Leaf~mosaics ; comparisons of stems and

leaves flowers and their insect -visitors .

Autumn — Fruits and fruit-dispersal ; autumnal t ints ;leaf-fall roads as highways for fruit-dispersal .

Many examples of organs adapted for special purposes

will be found , and the following should be studied

(I ) Shrubs with thorns and prickles

(a) branch- spines— Hawthorn (Fig . 2 1 9, Blackthorn , Gorse .

(b) pri ckles— Roses , Brambles, Gooseberry (prickleson the leaf-base)

(c) leaf- spines— Holly and Barberry1(Fig . 2 1 9, 2 , 3 ,

1 The Barberry has two kinds of shoots : (a ) long shoots bearingleaves reduced to branched spines (F ig . 2 1 9 , 2 and 4 , Ls) in theax ils o f these arise (b) dwarf shoots (Fig . 2 1 9 , 2 , a.s) bearing severals imple fo liage-leaves, each having a joint near the base (F ig . 2 1 9 ,

ECOLOGY

(2) P lants with nectaries on their leaves (extra-floral

nectaries) Guelder Rose (Fig . 2 1 9, Bird Cherry ,Wild Cherry (Fig . 2 1 9, and Bracken .

9.

FIG . 2 1 9 . MODIFIED SHOOTS AND LEAVE S .—I

, Hawthorn ; 2 ,

Barberry ; 3 , base of Barberry leaf ; 4 , spiny leaf on long shootof Barberry ; 5 , leaf Of Guelder Rose 6 , leaf o f Ch erry ; 7 , shooto f Cleavers with hooked fruits ; b.s , branch -spine ; d .s , dwarfshoot j, jo int ; l .s , leaf-spines n , extra-floral nectaries st, stipu le .

Climbing plantsThese are very numerous, and all the main forms

may be found and theirmodes of growth observed .

(A) Hook climbers or Scramblers . Brambles,Cleavers (Fig . 2 1 9,

(B) Root climber . Ivy (Fig . 222 ,

PLANTS OF HEDGEROWS AND WALLS 34I

(C) Twining stems , twining either

(a) to right or left indifferently— Woody Nightshade . (Also by means of its leaf-stalks . )

(b) clockwise (i . e . left to right or with the sun)— Hop

,Black Bryony (Fig . and Honey

suckle .

(c) Contra- clockwise (i . e . right to left or against

the sun) —Bindweeds .

(D) Sensitive organs (tendrils)(a) Branch tendrils —White Bryony (Bryoni adioi ca) (Fig .

(b) Leaf- stalk tendrils —Clemat is (Fig .

(c) Leaflet tendrils— Bush Vetch (Fig . 220 ) andClimbing Fumitory

The Ivy is well adapted to the conditions of life in a

hedgerow or wood, and possesses many points of interest .If it s long slender branches spread out on the ground the

leaf-blades face upwards . Commonly the branches climbthe trunks of trees by pressing their groups of advent itious

roots into irregularities of the bark , where they adhere

firmly and serve as holdfasts (Fig. 222 , The leaves arise

spirally on the axis , and in their broad bases the budsare part ly embedded . The leaf-bases are sensitive moti le

organs , and a very slight movement in this region carr iesthe blades at the ends of their long stalks through a wideare away from the shade towards the light by further

movement at the top of the leaf-stalk the blades are so

placed in relation to each other as to form good leaf—mosaics,and the t ips all point downwards . The upper surface of

the blade is glossy and concave , and the drainage—channelsare directed towards the apex

,which serves as a drip-tip

thus rain and snow qu ickly drain away . Observe the

behavi our of the Shoots which overtop the tree-trunk or

a wall and thus lose support and shade . On such shoots

342 ECOLOGY

adventitious roots are not formed the leaves arise in fiverows as before , but being illuminated on all sides the basesdo not bend , and the blades are not all directed to one

side (Fig . 222 ,they are also smaller and simpler in

outline . In October or November these Shoots produce

FIG . 2 2 2 . IVY .— I , c limbing shoot 2

, section through leaf-base ,

showing embedded bud ; 3 , flowering shoot ; 4 ,flower -bud ; 5 ,

flower seen from above 6,flower in side V iew 7 , vertical section

o f flower ; 8 , fru it ; a .r , groups of adventitious roots ; b, bud ;

d, d isk Lb, leaf -base p,

petals s , sepals st, stem .

umbels of flowers which possess several pecu liar features .

Often one or two flowers are formed before growth of the

umbel ceases , and these are left behind on the axis . The

flowers (4 , 5 , 6 , and 7) have five sepals, which are so small

that the five green petals which protect the inner organs

may be mistaken for a calyx five stamens alternate with

344 ECOLOGY

disturbed ground become covered by plants . The first to

invade and colonize the ground are annuals with goodseed-dispersal mechanisms ; these are in turn succeededby perennials, many of which have effective means of vege

tatiy e propagation . The effect of shade and of exposure

on plant -distribution is obviou s when we note how numerousare the Species on

,the sunny side

,and how few on the Shady

side ,o f a hedgerow . Similar differences may be seen in

hedgerows on Opposite S ides of a road running east and

west .Walls

In some districts,walls become so overgrown that , when

seen from a distance, they resemble hedgerows . This isoften the case in areas covered with glacial débri s and where

stones of various Shapes and sizes are abundant in the soi l .

When the land is brought under cultivation , the stones are

removed and used for bu i ldingwalls , often of great thickness .The interstices are filled with small stones and earth , forming a soi l which is very porous, and from it the water soon

drains away . Seeds which are depos ited in the crannies

by the wind or animals may germinate , but as the plants

grow they are liable to suffer periodically from drought .

It i s usual to find,therefore , that plants which succeed in

such a habitat are provided with devices to reduce transpiration ; the leaves are either very small or arranged in

roset tes , and often modified as water- storage organs . Manyo f the species are familiar as rockery plants , e . g . fleshy

leaved forms like the S tonecrops , Saxifrages, and WallPennywort (Fig . Heaths, Hai r- grass ,Gorse , and Broomhave reduced and wiry leaves . The Ivy- leaved Toadflaxhas S lender trailing stems and fleshy leaves ; the stalks ofits ripening fru its bend away from the light , lengthen , andcarry the capsules into the crannies , where the seeds are

shed . The Ferns found growing on the wall are all hardykinds , e . g . Wall- rue , Black Spleenwort , and Polypody .

WOODLAND PLANTS 345

CHAPTER XXV I I I

WOODLAND PLANTS

Features to observe in the study of a wood — The vegetationof woods varies considerably in different localities , according to elevat ion , slope , and aspect , nature of the soil , and

water- supply, but in all cases the striking Species are the

trees . In the study of woodland plants an attempt Shouldbe made to answer the following questions and to make

the following observations

(I ) Which is the dominan t Species of tree : i . e . whichSpecies is it that on the whole makes its influence mostapparent

(2) What are the subordinate trees

(3) Does their arrangement or the Character of the speciessuggest artificial planting

,or have the trees grown spon

taneously and formed a natural wood

(4) Look for seedlings , and see which trees are repro

ducing themselves from seeds .

(5 ) What are the dominant species of the ground flora

(6) IS their distri but ion influenced in any way by the

overshadowing trees

(7) Compare the shade produced by the different speciesof trees , especially that of Beech , Elm , P ine ,

Oak,Common

Ash , and B irch .

(8) IS the vegetation the same under trees with a close

canopy, like the Beech and Elm (Shade-endurers) , as

under trees with an open canopy, like the Oak ,Ash

, or

B irch (light -demanders)(9) Compare the parts closely planted with the more

Open parts .

(1 0 ) What i s the nature o f the soi l , (a) si liceous or calcareous , (b) coarse , stony ,

shallow, and dry ,or fine-

grained ,

346 ECOLOGY

deep , and moist (c) IS the soi l covered with humus , andif so , to what depth

(I I ) What is the aspect and how is drainage affectedby S lope, dip of the rocks , or other causes

(I 2) If differences are met with in these respects , do youfind accompanying Changes of species

(1 3) If the wood contains a wet hollow or if a streamruns through it , compare the plants (both trees and

undergrowth) of the wet parts with the drier part s Of

the wood .

( 1 4) Compare the undergrowth of the wood with that

of adjacent fields . To what extent are the Speciessimilar

(I 5 ) How will such a comparison help to decide between

(a) a recent plantation and (b) an old woodSelect a typical piece of woodland and mark out a narrow

strip across it,as indicated in Fig . 223 ,

r,A to B . This may

be subdivided into convenient squares and the parts studiedalong the lines indicated . Afterwards a more extended

study may be made,and the results recorded on compara

tive maps,as in Fig . 223 ,

r,2,and 3 , of which 1 is a treemap ,

2 a map of the common plants of the undergrowth , and

3 a soi l map .

From studies of this kind , we learn that , by a combina

tion Of factors such as increased shade , a mo ister atmo

sphere, more humus in the soil , a more regular water- supplyto the plants

,and protection by the overshadowing trees ,

an assemblage of plants is met with in a wood which differsin many respects from the adj oining vegetation . We

Shall also find that if trees are planted on pasture- land ,

the undergrowth for a time will consist of pasture—Species,but these will eventually give place to species which can

better endure the shade , and the ultimate flora will be determined by soi ls

,water- supply , and the other above-named

factors .

348 ECOLOGY

with stony débris and washed-down material from the

weathered sandstone edge . This débris rests upon a bed

o f fine-grained impervious shales, but the steepness of the

slope secures good drainage . The lowest part,beyond

the influence of the weathered sandstone, has a deeper andmoi ster soi l formed from the shales , and is covered byhumus several inches in thickness .The dominant tree is the Sessile Oak , the subdominant

ones Birch and Scots P ine, with occaSIonal trees of Mountain Ash , Holly, and Hawthorn . There is also a smallgroup of Beeches . In the upper part the trees are small ,produce little shade, and the undergrowth consists of Ling,Bilberry, and Hair-grass . Bracken , which is also abundant , has thick hard leaves . A little lower, on the stonyS lope , Ling is less abundant , Hair-grass and Bracken are

dominant , and there is also Bedstraw, Tormentil , Cowwheat , &c . In the lowest part , where the soils are deeperand moister

,the heath -plants give place to a society of Soft

grass, Bracken , and Bluebell , the Bracken here , however,having thinner and larger leaves than that of the upper part .

In a wet hollow in an adj oining portion of the wood occursuch trees as Alder , Willow ,

and Bird Cherry, as well as

the characteristic trees of the wood , while the ground flora

consists of Marsh Marigold ,B i tter Cress , Lady

’s Smockor Cuckoo Flower

,Greater S titchwort , Marsh S titchwort ,

Marsh Violet , Hogweed ,Sanicle, Yellow Deadnettle ,

Narrow- leaved Thistle ,Garlic , Rushes , Lady and Male

Ferns, and twenty other Species .

We thus see that in the drier, well—drained parts , the

species are fewer, and often possess small , up- rolled or backrolled leaves and other modifications , which enable them

to withstand drought . But when the water-supply is

constant,many more Species are able to exist and they

possess no such extreme forms as do the species characteristic Of the drier and more exposed parts . We Observe ,

FIG . 2 24 . OAK WOOD IN S UMMER .

FIG. 2 2 5 . OAK WOOD IN S P RING .

— Gr0 und flora of

Soft- grass , Bracken ,and Blu ebell .

FIG. 2 2 6 . TH E SULPHUR TUFT TOADS TOOL (Hypholoma

350 ECOLOGY

the seasons forms an interesting study . In the winter, treeand shrub layers stand out in sharp contrast

, as in the caseof leafless Oak and evergreen Holly . S till more strikingis the Spring aspect Of Ash and Hazel

, the early brightgreen foliage of the latter being very conspicuous against the

grey branches and black unopened buds of the Ash . The

green winter carpet of grasses and mosses is followed inthe Spring by low-growing plants (Fig . 225) like the Bluebell , Anemone ,

P rimrose ,Cowslip , and Celandine , to be

succeeded in the summer by the taller- growing Bracken

and other ferns . Meanwhile, the leaves of the trees are

expanding, and by their ever- deepening Shade, protect

the tender plants of the ground flora .

Complementary soci eti es .

— The diagram (Fig . 227) willhelp us to appreciate the significance of such adaptations

in the ground flora Of an Oak Wood where the three plantsillust rated commonly grow in Close association . In the looseleaf-mould on the surface run the rhizomes Of the Soft-grass .

Beneath this , in the dark soil containing much humus , arethe rhizomes of the Bracken , while in the fine yellow loambelow are the bulbs of the Bluebell , though young bulbs

on thei r way downwards may be found in the other twolayers . In November the young green blades of the Soft

grass appear , and through the winter and early spring forma bright green carpet . Meanwhile,

the leaves of theBluebellcome above ground , to be followed in the early spring by

a wealth of flowers (Fig . Towards the end of theflowering period , and as the fruits are ripening , the Bracken

unfolds its fronds , and raised on tall stalks above the topsof the young Bracken are the flowers Of the Soft-grass .

In the late summer and autumn the mature Bracken - frondsform a continuous cover . Eventually they die down to

form a warm winter carpet . Thus thei r soil- requirements ,thei r modes of life ,

thei r periods of active vegetativegrowth

,thei r times of flowering and fruiting, are for the

FIG. 22 7 . COMP LEMENTARY S OCIETY IN AN OAK WOOD .

A, Soft -grass B,Bracken and c , Bluebell .

352 ECOLOGY

most part different . Species growing mutually togetherin this way form a complementary society . Referenceto the maps (Fig . 223 ,

r and 2 ) will Show'

that these threespecies do not always grow together . In places you willfind that one may grow to the exclusion of the o thers .

Under the deep Shade of the Beech , the Bracken seldomoccurs

,but the Soft-grass is frequent , and sometimes the

only species is a weak form of Bluebell . The latter also

occurs on the stony Shallow soil among the Hair-grass .Types of B ri tish woodlands — There is very li ttle natural

woodland in the British Islands . P lantations are numerous ,and some of these

,being on the sites of native woods , pre

serve many of the features of primi tive forest . The wood

lands of Britain may be divided into two main groups ,namely :

( 1 ) Woodlands on si liceous soi ls : Clay ,loam, and sand .

(a) Alder-Willow wood : a lowland type with a ground

flora of marsh -plants

(b) P edunculate Oak wood , with a flowery carpet o f

moisture- demanding species

(c) Sessile Oak wood , on drier , often sandy, soil a type

of which has been given above (Fig . 223)

(d) Oak-Birch-Heath wood , with a ground flora of

heath -plants

(e) Birch wood : characteristic of the northern up

lands , in which the Birch is the dominant tree

(f) P ine wood : this type differs from the above de

ciduous woodlands in being composed mainly of

evergreen coniferous trees .

Native P ine woods occur in Scotland , and were formerly

extensive in England . The ground flora is usually of the

heath type ; and seedlings Of the native Scots P ine oftendevelop freely on heather moors , both lowland and upland ,and form a P ine—Heath wood . Many of the present P ine

woods are plantations , and exotic conifers are commonly

354 ECOLOGY

other trees and Shrubs , and the ground flora is veryscanty (Fig . The more common trees are

Gean (P runus avium) and Yew ; the latter some

times forms a shrub layer , as do the Hazel and Holly

in Ash and Oak woods . The characteristic Species

of the ground flora , especially in'

th e lighter parts ,

are Dog’s Mercury, Sanicle , Violets (V . sy lvestris,

V . Riviniana,and V . hirta) , S trawberry, Enchanter

’

s

Nightshade,Helleborines , Large Butterfly Orchis ,

and the saprophytes , Bird’s- nest Orchis and the

Yellow Bird’s -nest (M onotropa) also the Green and

S tinking Hellebores , Deadly Nightshade,Spurge

Laurel , and Butcher’s Broom (Ruscus aculeatus) .

CHAPTER XXIX

PLANT—LIFE IN HUMUS

Abnormal Modes of Nutrition

The work of Fungi in humus— The surface layers of thesoil containmuch organicmatter , and are commonly covered

by the remains of plants which are the accumulations ofsuccessive years of growth . In meadows and pastures , thistangle of vegetable matter, living and dead , forms theturf . In woods , we know it as leaf-mould or humus ;and it is often many inches in thickness . On the moors,i t forms deep beds of peat . Examine the leaf-mould ina wood , and , on lifting it from the ground , note that thedecaying leaves are Often held together by a white , feltlike mass of mould- threads . This felt is the vegetativepart of various Species of Fungi and is known as the

my celium . From this mycelium arise the fruit -bodies ofthe Fungi , some of which we are familiar with asMushrooms

PLANT-LIFE IN HUMUS 355

and Toadstools (Fig . The threads (or hyphae) Ofthe mycelium Obtain their food from the dead leaves and

other organic matter ; and , along with organisms l ike

bacteria , are responsible for their decay. The Toadstools ,therefore

,live upon the complex organic substances of

dead leaves and twigs , or on an imal remains and exore

ments whereas the food Of green plants consists Of

solut ions of certain mineral salts and carbon dioxide .

AS there is much available energy in the organic compounds

in humus , Fungi , by making use Of this , do not need toabsorb light—energy , and can th rive without developing

either leaves or chlorophyll .

S aprophy tes , My corrhi za ,and Symbi osi s

— P lants growingupon dead organic matter (animal or vegetable) are calledsaprophytes (Gr . sapros rotten) . Some fungal sapro

phytes are very restricted in their distribution , and occur

only on the fallen leaves of particular species of trees .

You will find mycelia abundant in the damp leaf-mould

of woods,and the roots Of plants growing in the mould

Often become intimately surrounded by hyphal threads .

Sometimes the hyphae enter the tissues Of the roots and coi l

up within their cells (Fig . 229 A) . They gain an entrance ,not merely by mechanical pressure , but also by means of

a ferment which they secrete and which digests the cell

walls Of the roots with which they come into contact .

Usually they do no harm to the roots , and possibly they

convey to them useful materials from the humus .

Fungi thus do an important work they decompose the

cast - Off leaves , prevent their accumulation ,and convert

their constituents into useful food for green plants .They may even convey this food into the t issues of theplants . In return they receive Shelter and possibly some

food from the roots .

Such a combination of fungal hyphae and the roots ofplants is called a mycorrh iza (Gr . myke

'

s a fungus,z z

356 ECOLOGY

rhi z a a root) , and a very large number Of plants which

grow in humus, trees and Shrubs as well as herbaceousspecies , have a mycorrhiza on their roots . These plantshave normal green leaves , and their mode Of nutrition is

,

on the whole ,the same as that of typical flowering plants ;

but by association with fungal hyphae they d irectly or

indirectly utilize the humus . The union of two organisms

whereby they mutually benefit is called symbiosis (Gr .

syn together, bios life) .The best example of symbiosis is found in Lichens , so

commonly seen as leafy incrustations on walls and treetrunks , or as grey branching threads on the ground , like

the Reindeer Moss . A Lichen , though usually regarded as

a distinct plant , is really a colony of plants of two kinds

the predominant one is a fungus , and this entangles within

the meshes of its mycelium innumerable green , algal cells .The fungus protects or imprisons the algae and suppliesthem with mineral food , out of which the latter , by virtue

of their chlorophyll, bui ld up organic materials, which in

turn are absorbed as food by the fungus . We have already

not iced (p . 326) the case of symbiosis in leguminousplants , wh

’

ere root -nodules are formed as the result of

the act ion of bacterioids which enter the root-hairs . The

Alder and Sea Buckthorn are further examples .

P lants that live entirely on humus or other dead

organic matter are generally lowly forms like Fungi , and ,

aswe have seen , have no need for and do not contain chloro a

phyll in their tissues . Some flowering plants grow in the

humus of woods and , like the Fungi , live entirely upon it .

Very few Brit ish plants are able to subsist in this waysome of them are Orchids , e . g . the B ird ’

s -nest Or chid

(Neottia Nidus-avis) and the Coral -root Orch id (Corallo

rhi z a) . Another , belonging to the heath family, i s theYellow B ird’s—nest (M onotropa Hypop i tys) , and all havemycorrhiza on their roots or rhizomes .

358.

ECOLOGY

P arasites .

-Not only do dead and decaying leavesprovide a habitat for many plants , but commonly living

plants (and even animals) provide habitats for manySpecies , especially Fungi . Familiar examples Of this are

the rusts , mi ldews , and blights , which often destroy valuablecrops . A plant which l ives at the expense of anotherorganism is called a parasite and the organism upon whichthe parasite preys is known as the host The guest , however , is uninvited and takes advantage of the

‘ hospital ity

to the injury of the host and Somet imes causes its death .

Living habitats are Often selected by plants other than

Fungi , e . g . many flowering plants prey to a greater or lessextent on their neighbours . The most familiar example

i s the Mistletoe, which grows perched on the branches of

the Apple, Poplar , and other trees . Birds eating the berries

are unable to swallow the seeds because Of the sticky

material around them , so they scrape them off on to thebranch ,

where they germinate . Suckers enter the branch

and form a union with the wood of the host from whichthey draw the mineral food for themistletoe . The influence

of this mode of nutrition is seen in its yellow- green leaves ,which contain chlorophyll, and the products of . photo

synthesis enable the plant partly to maintain itself . The

leaves , too , are evergreen , and are able to form organic

substances at favourable periods throughout the year .

These may be passed downwards and contribute somewhat

to the nourishment of the host when the latter is not in leaf .

The Mistletoe, therefore,is not ent irely dependent on its

‘ host ’

for food , and may be regarded as a partial parasite .

Many flowering plants are partially parasitic , and attachthemselves bymeans of suckers to the roots of neighbouring

plants, especially grasses . They produce green leaves andclosely resemble plants which obtain their food in the

normal manner . Examples are Cow-wheat , Eyebright ,Yellow Rattle , and Louseworts . The leaves of the Yellow

PARASITES 359

Rattle are, as in the Mistletoe , often pale—green , and thoseof the Louseworts are red or reddish-

green .

A few flowering plants are entirely dependent on hostplants for food . Some of these, like the partial parasites

above ment ioned , attach themselves by suckers to the

FIG . 2 29 . TOOTHWORT .

I , part of underground stem2

, roots ; h .r, root o f host

p lant P .r , root of parasites, suckers attached to hostse

, scale - leaves .

FIG . 2 30 . TWINING S TEMOF DODDER ATTACHED B Y

SUCKERS To THE S TEM OF

HOP

FIG . 2 29 A . SE CTION OF ROOTOF L ING SHOW ING MYCORRHI Z A .

roots of other plants, e . g . the Toothwort (Lathraea squa

maria) and the Broomrapes (Orobanche) .The Toothwort , frequently found in hedgerows and

woods , possesses many features in common with sapro

phytes like the Bird’s -nest Orchid and Coral - root

,e . g . i ts

36o ECOLOGY

vegetative organs are underground, i ts leaves are reduced

to scales , only the flowering shoot comes above ground ,

and the plant is a sickly yellow or purplish colour with

li ttle or no chlorophyll in its tissues . The rhizome is thickand bears four rows of curious scale- leaves (Fig . 229 ,

which are thick and fleshy,and back- rolled in such a way

as to give rise to a branched cavity opening to the exterior

by a narrow S lit at the base . Very small animals oftenenter the cavities and die there

,and the products of thei r

decay may be absorbed ; while special cells in the wallsof the cavities may serve for the excretion of water . The

roots form disk- like attachments (Fig . 229, 2 s) on the rootsof trees such as Hazel , Elm ,

and Beech,and suckers from

the disks enter the tissues of the host and absorb nu triment i t is also probable that some nutriment is absorbedfrom the humus after the manner of saprophytes .

Several species of Broomrapes occur in Bri tain and are

parasitic on the roots of such plants as Broom,Gorse,

Clovers , Hemp , and Ivy . They are dirty white or yellowishin colour , or tinged with pink and

,like the Toothwort ,

send only thei r flowering shoots above ground .

An extreme example of parasitism is found in the Dodders .These

,however, are stem-parasites , and they possess many

remarkable features . The seed , on germination , sends its

radicle a very short distance into the ground , while the

slender stem nutates , and is sensitive to contact likea tendril (Fig . If i t comes in contact with a hosti t twines round the stem and sends a sucker or haus

torium (Fig . 23 1 ) into i t , and both the wood and the bastof the haustorium form a union with the correspondingtissues of the host . By this means the Dodder can obtainthe whole of the food it requires . The root now dies away ,

and the S lender stem,which is without chlorophyll and does

not bear any green leaves , subsists entirely at the expenseof th e plant on which i t preys . As new branches arise they

INSECTIVOROUS PLANTS 36 1

spread over and twine around other stems and i t is an

interesting fact that usually only a few turns are made

around a single ‘ host —stem, but from these coils many

haustoria may be given off . In time, many bunches of

small flowers are formed , each flower being like a tinyConvolvu lus . Dodders (Cuscuta spp.) occur on a greatvariety of plants , such as Clovers , Vetches , Flax , Hop ,Gorse

,Ling , Bedstraw,

Thyme,Thistles , and Nettles ; and

theymay be so abundant as to do great damage to crops .Total parasites

,like total saprophytes

,show how de

generate and modified the vegetative organs become in

plants which have thus changed thei r mode of nutrition .

The flowers Show little or no modification except in colour,and much of the energy they derive from the

‘ host ’ isexpended in the production of an abundance of seeds .

Partial parasites and partial saprophytes aremore common ,

and Show intermediate stages of modification accordingto the degree of parasitism or saprophytism they have

reached .

Insectivorous plants .

— In a variety of ways plants may

entrap small animals . In the Toothwort , as we have seen ,there are cavi ties in the back- rolled leaves into which

small animals may enter . In the Teasel , the bases of the

Opposite leaves are united in such a way as to form a cup

which contains water, and insects , finding their way intothe cup , may become drowned . Often flower -stalks are

covered by glandular,sticky hairs to which small insects

adhere and die in large numbers . Some species of S i lene

have received in consequence the popular name of Catchfly In other plants more specialized traps are found

,

and the insects or other small animals caught in them may

contribute by their decay to the nutrition of the plant .Species which possess such peculiarly modified leaves or

shoots and supplement their nitrogenous food in this wayare known as insectivorous or carn ivorous plants .

362 ECOLOGY

Many of them occur in boggy or marshy habitats, usually

in soil poor in mineral food while some of them are water

plants . In all cases , however, they contain much chlorophyll in their tissues , and their general mode of nutri tionis like that of an ordinary green plant . The animal food

obtained by means of their traps is , therefore, only supplementary . S till

,their capturing devices are ingenious and

curious . They may take the form of ( 1 ) sticky hairs orsticky and sensitive tentacles (2 ) trap- like bladders andpitchers ; and (3) sensitive leaves which form rapidlyclosing traps .Two examples , the Sundew (Fig . 232) and Butterwort

(Fig . 234, r , are locally abundant in boggy places onthe moors

,both in hilly districts and on lowland moors .

Three species of Sundew occur, the most common one

being the Round- leaved Sundew (Drosera rotundif olia) . Iti s a small plant

,only a few inches high ,

whose slender rootsanchor the plan t in the wet soil

,or among bog moss , and

the leaves form a rosette pressed close to the ground . Atthe end Of the leaf - stalk is a circular, reddish blade, fringedwith long

,clubbed tentacles , and similar , but Shorter,

tentacles cover the upper surface . The lips secrete a

sticky, viscid fluid , forming shining dew- like drops , attrac

tive to insects . The secretion is mistaken for honey, and

i f a small insect alights on some of the tentacles at the

edge of the leaf i t is held firmly by the secretion . The

tentacles are very sensitive to pressure, and the stimulus

given by the insect in its struggles to escape results in the

tentacles bending over ; and the stimulus may extend to

other tentacles and they also bend over , and so carry the

insect to the centre of the blade , where i t is brought intocontact with other drops and eventually i t is smothered

(Fig . 23 The secretion of the tentacles is now changed ,and a ferment is poured out which digests the proteincompounds o f the insect

’s body, and these digestedmaterials

364 ECOLOGY

FIG . 2 34 . INS ECTIVOROUS P LANTS — I,Bu tterwort ; 2

, the same

showing leaves strongly reflexed when taken from th e ground3 , branch of Bladderwort 4 ,

bladder enlarged ; 5 , 6 ,leaves o f

P itch er-plants ; 7 , leaf of Venus’ Fly -trap

,Open 8

, the same c losed

bl , bladder ; h . sensitive hairs ; t, tendril .

INSECTIVOROUS PLANTS 365

3 and These have suggested both the common and

scientific names for the plant— Bladderwort and Utri cularia .

Several species occur in Britain , and all are remarkable in

that they never possess roots . The shoots float freely in

the water , but when in flower,the inflorescence is raised

into the air . The bladders are curious eel~traps filledwith water and provided with doors which open only

from the outside . Small aquatic animals may enter, butare unable to escape . After swimming about for a time,

they die and are decomposed by the action of bacteria ,

and the products of their decay are then absorbed bythe bladder . The Bladderwort probably does not secretea digestive ferment and thus its mode of nutrition is that

Of a partial saprophyte.

In the Indo Malayan region and elsewhere , a number ofbog

-plants occur which have large and remarkable water

pitchers , and many of these may be seen in hothouses andbotanic gardens . Fig . 234, 5 and 6 , Shows the leaves of

two Of these P itcher-plants , which are species of Nepenthes .

The midri b of the large leaf—blade is continued as a long

tendril (t) , which serves as an organ of attachment to a

neighbouring plant , and the tip develops into a large pitcher

with water at the bottom and overhung by a lid . Round

the mouth is a firm, smooth rim, proj ecting inwards and

fringed with Sharp teeth . The outer surface is blotched

with various Shades of red , brown , and green , and so isattractive to insects . At the entrance are honey-glands ,and below them the surface is glazed and smooth , forminga slide- zone On reaching this , insects find it easy todescend into the water, where they are drowned . Digestionis brought about by ferments secreted by the glands of thepitcher.Some pitchers are formed from whole leaves , as in the

S ide-saddle Flowers (S arracenia) of North America ; whilein Cephalotus, an Australian P itcher-plant , division of labour

366 ECOLOGY

exists,some leaves having normal flat green blades , and

others being transformed into pitchers .

A more complicated device is found in the Venus ’

Fly -trap (Di onaea muscipula) (Fig . 234, 7 and a plant

growing in mossy places in the woods of Carolina . Itsleaves , like those of the Butterwort , form a rosette close to

the ground ; the leaf -stalk is winged (phy llode) , and the

blade,slightly bent upwards along the midrib ,

is fringedwith long

,comb -like teeth . Many glandular hairs cover the

upper surface, and on either S ide Of the midrib are threelong j ointed hairs (Fig . 234, 7 h) . These are sensitive

,but

if slightly touched once no result is observable if , however ,a second stimulus is soon applied the blade suddenly closes ,and i f an insect supplies the stimulus it is at once entrapped .

The teeth along the edges interlock,and the two halves of

the blade draw Close together . A digestive secretion is

now poured out over the body of the insect and the digestedmaterials are absorbed by the leaf . Later it expands in

readiness for more food .

The advantage to insectivorous plants of this mode o f

nutrition is in the gain of ni trogen and nutritive salts supplied with the nitrogen compounds , and the plants thussupplied with animal food thrive better than those livingsolely on inorganic materials .

CHAPTER XXX

GRASS -LANDS : PASTURES AND MEADOWS

A LARGE part of the Bri tish Islands is devoted to pastur

age, about one—half of England , three—quarters of Wales ,one -half Of Scotland , and three—quarters of Ireland beingso utilized . Some of this is mountain and heath land , butthe greater part is permanent pasture dominated by grasses .

GRASS -LANDS : PASTURES AND MEADOWS 367

Thus a greater area is covered by grasses than by any other

type of plant . Favoured by good methods Of vegetative

increase ,social hab i t , and great range of species suited to

very varied condi tions , they form one of themost important

vegetation features of temperate regions , e . g . the extensive

pastures and meadows of Europe, the steppes of Russia ,

and the prai ries and savannas of America . They com

mouly form extensive carpets , as in our pastures and

meadows , and their numerousleaves and the accumulatedremains of rhizomes and feltedroots form turf or sod .

Grass moors .— On the Shaly

s iliceous P ennine S lopes large

areas are dominated by grasses

(Fig . two Species being

especially conspicuous . The

Mat—grass (Nardus stri cta)(Fig . 236) in the summer

forms large tussocks with

grey -green,wiry

, up—rolled

leaves (Fig . 25 5 , in theautumn it turns a light yel FIG . 2 36 . MAT-GRAss .

— P art

lowish -brown,colouring the Of a tussOCk ShOW ing th e

c losely-packed shoots on th emountain - S ides and forming rhi zome .

a conspicuous feature in thelandscape ; it is easily recognized in the winter by

its one- S ided empty spikelets .Along with it

, and Often becoming dominant over cons iderable tracts

,is another tussock- forming species , the

Waved Ha ir—grass (Deschampsia flexuosa) . Its leaves arestill finer than that of the Mat - grass

,and up

—rolled so as toleave only a very narrow groove (Fig . 255 ,

The Bent (Agrostis vulgaris) and Sheep’s Fescue (F estuca

ovina) (Fig . 255 , both with up- rolled leaves , are very

368 ECOLOGY

abundant , especially at rather lower levels . Associated withthese in the drier parts are many heath-plants

, e . g . Ling,

Cross- leaved Heath (Eri ca Tetralix) , and B ilberry . In thewetter parts of these grass moors the ground is occupied byhuge tussocks Of the Purple Moor-grass (M olinia caerulea) .In spring its pale yellow-green leaves

,especially those

following the burning Of the moor , are very striking .

Calcareous grass-land .

—Very different are the calcareousgrass -lands Of the hill-slopes of the mountain limestone andthe great sheep-grazing grounds of England , the ChalkDowns . The Mat -grass , Waved Hair—grass

,and Purple

Moor -grass are absent , and in place of their tussocks wehave a much Shorter grassy turf dominated by the Sheep

’sFescue -

grass (F estuca ovina) , and with it the Lesser Meadow

Rue (Thalictrum minus) , Lady’

s Fingers (Anthy llis Vulneraria) , Horseshoe Vetch (H ippocrep is comosa) , the LesserBurnet (P oterium S anguisorba) , the Rock Rose (H elian

themum Chamaeci stus) , the Lesser Scabious (S cabiosa Columbaria) , and the Hoary P lantain (P lantagomedia) , all of which

are absent from siliceous grass—land .

Neutral grass-land .

— Where much leaching has occurred ,on calcareous Slopes , heath -plants are found alongside

typical calcareous species . They are small at first and

hidden by the grass but in places they become dominant

and form a limestone heath . When grass -land is heavily

grazed and manured ,the number of Species is , as a rule,

reduced , and the typical plants of the two previous typesof grass - land are rare or absent . This is called neutral

grass -land and is dominated by such species as the Rye

grass (Lolium perenne) , Vernal—grass (Anthoxanthum odora

tum) , Cock’s Foot -grass (Dacty lis glomerata) , Yorkshire Fog

(Holcus lanatus) . Many of these species , however , may

occur within a limited area,and much may be learnt from

a careful study of an Old pasture or a meadow .

M eadows — Because of their higher cultivation , meadows

370 ECOLOGY

Yellow Rattle . The delicate roots of the last two species

are often attached to the roots Of grasses , from which they

absorb part Of their nutriment .

At the lower level , where the soil is finer—grained , wetter,and lies over a bed of shale,

the plants are quite d ifferent .

The rolled- leaved grasses are displaced by grasses withlarger flat blades , such as Cock’s Foot , Meadow Fescue, and

Yorkshire Fog ,while flowering plants like Lesser Spearwort ,

Ragwort , Knapweed , Lousewort , Yarrow, Red Campion

and Wood Betony occur .

In a limestone pasture, however, species likeWi ld Thyme,Yellow Violet , Lady

’s Fingers , Burnet , Yellow Bedstraw ,

Small Scabious , Hoary P lantain , Blue Sesleria,Sheep

’

s

Fescue—grass , and others are found .

CHAPTER XXXI

WATER AND MARSH PLANTS

Vegetation of a pond .

— Examine the vegetation of

a pond or lake,and compare the plants Of the banks with

those growing along the water’

s edge, and also with those

extending into the open water (Fig . At the inlet ,look for the stages in the development of a marsh , and

not ice how invasion of the pond takes place (Fig .

Draw a transect , e . g . Fig . 239, through the pond ,includi ng

a portion of the bank ,and Show in a diagram the succession

of plants met wi th . The upper part of the bank (A) iscovered by meadow—Species, but near the wetter soils be

low (B ) , these gi ve place to Rushes , Purple Loosestrife,Water Dropwort . Iris , Marsh Marigold ,

Lady’

s Smock ,Large Bit ter -cress

,Bog St itchwort , Ragged Robin ,

Meadow

sweet , Lesser Spearwort , and Bog Starwort .

Nearer the water’s edge is a belt of reed -like plants

FIG. 2 37 .

WATE R- P LANTS INV ADING A LAKE .

FIG. 2 38 . MARGINAL V EGE TATION OF A P OND ; WATE RBUTTE RCUP S EXTENDING FAR INTO TH E WATER .

372 ECOLOGY

surface by a leathery cuticle (Fig . P lants like these,

which bear different kinds of leaves , are said to be‘

hetero

phy llous (Gr . heteros different ) . Heterophylly is commonin water-plants and frequently occurs in land—plants .The Frog-bit has float ing leaves and much -branched

roots hanging in the water , but Often not rooted in the soi l

(Fig . 239,E) . The Duckweeds , with thei r curious leaf- like

stems (phylloclades or cladodes ) and roots hanging in the

water, are entirely float ing . In the more Open water many

plants occur wh ich are rooted and ent irely submerged ,

e . g . Water Milfoi l , Canadian Water-weed, Stonewort s, and

many Pond—weeds ; while plants like the Bladderwortshave neither root nor floating leaves , but are suspended

unattached in the water .Growing among these i s a rich flora of minute plants ,

the Algae ,some in the form of a tangle of delicate green

threads and others , though consisting each of a S inglemicroscopic cell, exhibiting, as in the case of desmids anddiatoms , structural detai ls which are both elaborate and

beautiful .

S tructural peculiari ties of water-plants .

— Specimens of

the di fferent types Of water-plants should be obtained ,

and their varied forms studied wi th especial reference totheir aquatic surroundings , on account of which waterplants form a d istinct type of vegetation .

Cut sections Of stems and leaves Of the larger Species andexamine them wi th a lens . Note that the bulky cortexcontains very large air-spaces (Fig . and these occurnot only in stems and leaves , but also in the roots . The

roots gr owing amongst decaying organic matter, and inbadly—aerated mud , are thus able to obtain a supply of

air by diffusion from the shoots above . The vascularbundles of the stem , as in roots (Fig . are Oftenconcentrated in the centre , which is a good position for

resisting the longitudinal strain of running water . The

FIG . 240 . WATE R-P LANTS IN A D ITCH . In th e foreground Arrowhead , and beyond th e Common R eed with leaves ind icating th e

d irection o f th e wind .

FIG . 2 4 1 . FLOATING LEAVE S OF TH E YE LLOW WATE R L ILY .

374 ECOLOGY

and therefore not read ily eaten by such aquatic animalsas snails . The epidermis is usually very thin

, and enablesthe plants to absorb through i t much of their food in theform of mineral salts and carbon dioxide di ssolved in thewater in which they live .

Invasion . Water-plants as land-winners .

— P lants growingin water are not subj ected to such extremes as plantsgrowing in the air

, and consequently grow rapidly ; the

rhizomes plough their way through the mud and give off

innumerable shoots into the water . This rap id vegetative

growth enables the plants to spread quickly, and they are

further aided by the ease with which detached Shoots growand form new plants . On the approach of winter , special

winter buds are formed inmany species , such as P ond-weedsand Frog-bit ; these break off, fall to the bottom , and restuntil the following spring . By such vegetative means ,rather than by seeds (see p . Water—plants reproducethemselves extensively, and rapidly invade the water .Interesting examples of this may be found in many

ditches , ponds , and lakes . Reed—like plants may be seento extend from the margin across the inlet . Their stems

and leaves form a filter, keeping back the mud , which ,

together with the remains of successive seasons Of plants ,chokes up the channel and provi des a soi l over which theplants f rom the banks push their way farther and farther .

Thus in time the pond or lake becomes converted into

a marsh .

By such invasion , plants become important land—winners .

The aquatic vegetation by its very luxuriance prepares the

way for its own extinction . It contributes to the changesof conditions which favour a drier type of plant -life, and

it is only a matter of t ime when it wi ll be succeeded by the

invaders . If further changes should result in improved

drainage , the marsh type will itself be supplanted . Inthis way invasion and succession follow each other in

WATER AND MARSH PLANTS 375

natural sequence, and form a widespread phenomenon .

A parallel example , as we have seen , is the invasion ofsand-dunes by grasses and sedges , whose very long rhizomesbind and fix the sand and prepare a soil on which a grassy

turf or a heath , and eventually a wood , may become

established .

Flowers of water—plants .

— The flowers of most waterplants are carried above the water

,and open in the air .

In a few cases they open and are pollinated in the water .This is seen in e . g . the Grasswrack, whi le some

,like the

Water B istort , may be self-pollinated under water , but the

flowers do not open , SO that really they are pollinatedin air and not in water . Usually

,however , the flowers are

at a disadvantage,owing to the scarcity of insect-pollinators

on water , but this is compensated for , as we have seen ,by

the great powers which water—plants possess Of vegetative

reproductionM arsh-plants .

— While there is every gradation betweenwater—plants and marshplants, typical examples differ in

several respects . The/aerial parts of marsh -plants agreeclosely in form and structure wi th those of land-plants ,and are exposed to S imi lar conditions ; the underground

part s grow in wet , cold , badly-aerated soil . In consequence ,

as in aquatics, some marsh-plants have large ai r—spacesin their t issues others have cylindrical stems and great lyreduced leaves , e . g . Rushes and Horsetai ls . Interest ing

modifications , related to differences in transpiration ,may

be easi ly seen in the Meadow—sweet . The lower leaves ,which are exposed to little evaporation , are wi thout hai rs

the intermediate leaves have patches of hairs on the lower

surface ; and the upper more- exposed leaves have a closecovering of silkyhairs ,whichmaterially reduce transpiration

The following is a list Of the common plants foundgrowing in a marsh at the head of a small lake which has

been invaded by the Pond-weed , Water Milfoil , Water

376 ECOLOGY

Horsetail , and Marsh Club-rush . Encroaching on theseinvaders were : Water P lantain , Common Reed ,

Bur- reed ,Soft Rush , Marsh Horsetail , Marsh Bedstraw,

Bog Stitchwort , Ragged Robin , Meadow-sweet , Hairy Wi llow-herb ,

Square- stalked Willow-herb,Lesser Spearwort , Great

Valerian , Large-flowered Bitter-cress , Lady’s Smock ,

Marsh Marigold , Brooklime , Water Forget -me-not , MarshThistle, Hemp Agrimony, Marsh St . John

’s -wort , TuftedHair-grass . Numerous trees surround the marsh , but onlytwo of the Species have invaded it , the Alder and Willow

These thrive well in the wet soil , and the marsh isbecoming converted into an Alder-Willow wood .

CHAPTER XXXI I

WEEDS

A CAREFUL examinat ion of a natural piece of vegetation

produces the impression of a natural blend of colour andform, and both are in keeping with the habitat . Such an

area contrasts sharply with a piece Of cultivated land,which

,

whether garden or farm , Shows an obvious selection and

arrangement of plants su ited to the needs or caprice of man .

Even here nature cannot be ignored , and i t impresses i tself

by topography ,soil , and climate in a manner which

compels even cu ltivation to keep along more or less definitelines . Nevertheless

,man ’s aim is to substitu te for the

less useful nat ive plants those needed by h im . In this waymuch Of the native vegetation is destroyed

,but an interest

ing meshwork persists along the hedgerows (Fig.

roadside patches , and in ditches and streams or some

WEEDS 377

peculiar topographical feature may render cultivation

impracticable, e . g . a steep bank , amoor, copse , or wood ,a mountain or fringe of the Shore, and here the native

plants maintain their footing .

(a) Cornfield W eeds

In order to render land suitable for cr0 ps , the farmer has

not only to destroy the native plants , but to change the

habitat as well , and this he does by ploughing , draining ,manuring

, and the like . On this freshly-made soil his seedsare sown

, and in time germinate . Meanwhile the surface is

exposed to invasion by the native plants which have escapeddestruction . Those with a good dispersal -mechanism , will

stand the best chance of Spreading ; others with runners ,such as the Silverweed , or the qu ick -growing rhizomes of

the Couch -grass , soon make headway . Unless care is taken

to eradicate them they will occupy the soil intended forthe crops

, and , being stronger and sturdier , will gain the

mastery . From man ’s point Of V iew these are plants inthe wrong place and he calls them weeds

If , however , we make a collection of the weeds of arable

land and examine them , we find that very few are of thesame Species as the native plants Of the district .The native plants are mainly perennials , while the weeds ,

like the plants man cultivates,are for the most part

annual s . The ground is prepared for annual crops , and

annual weeds find it a favourable soil , and thrive accordingly ; and as long as man disturbs the ground ,

perennialshave little chance of succeeding . Thei r opportunity comes

when cultivation ceases ; with a more stable soil , thesturdy natives soon invade the land

, and the annuals ,accustomed to rely on man for a suitable habitat , are

succeeded by perennials which have migrated from the

adj acent , more natural areas . Soon the land revertspractically to its original state .

378 ECOLOGY

Waste-heaps , quarry- tips,new embankments , or road

sides , furnish numerous examples of plant invasion and

succession and the plants of such habitats should be carefully studied as to their origin , means of dispersal , and

increase both by seed and vegetative propagation .

Native annuals occur along the coast , on the rocks , andon Shifting banks and some weeds which have somewhatfleshy leaves may have come origi nally from such habitats ,e . g . Fumitory (F umaria ofii cinali s) , Hedge Mustard

(S isymbrium ofii cinale) , Charlocks (Brassi ca Rapa and B .

S inapi strum) , White Charlock (Raphanus Raphanistrum) ,Goosefoot (Chenopodium album) , Orache (Atriplex patula) ,Black Bindweed (P olygonum Convolvulus) , Knot -grass

(P . aviculare) , P ersicaria (P . P ersi caria) , all of which are

annuals . The Mayweed (M atricaria inodora) is a biennial ,and another frequent weed , the Bladder Campion (S i leneinflata) , is a perennial . Other annuals have doubtlessbeen introduced with impure seed , and those with bright

and showy flowers have probably come from sunnier climes ,e . g . the P oppies (P apaver Rhoeas and P . dubium) , P oor

Man’s Weather—glass (Anagallis arvensi s) , and the Corn

Marigold (Chry santhemum segetum) . Many have beenintroduced in this way from North and Central Europe and

Asia .

Other common annual s are

Field Buttercup (Ranuncu lus arvensi s ) , Red P oppy (P apaverRhoeas) , Sheph erd

’

s P urse (Capsella Bursa -pastori s ) ,Corn P ansy ( Vi olatri color) , Corn Cockle (Lychn i s Gi thago) , Ch ickweed (S tellar i a medi a) ,Spurrey (Spergular i a arvensi s) , Soft- leaved Crane

’

s -bill (Geraniummolle) , Cut - leaved Crane

’

s -bill (G . di ssectum) , H erb Robert (G . Rober

ti anum) , Trefoil or Black Med ick (M edi cago lupu lina) , H op Trefoil(Tr ifolium procumbens) , Tare ( Vi ci a hi rsuta ) , P arsley P iert (Alchemi lla arvensi s) , Fool

’

s P arsley (Aethu sa Cynapium) , Cleavers (GaliumApar ine) , Field Madder (S herardi a arvens i s) , Cudweed (Gnaphaliumuliginosum) , Groundsel (S eneci o vulgari s) , Sow -thi stle (S onchus oleraceus) , Corn Forget-me-not (M yosoti s arvensi s) , Corn S corpion Grass(M y osoti s vers i color) , Ivy -leaved Speedwell ( Veroni ca hederaef oli a) ,

380 ECOLOGY

The most abundant weeds of grass -lands are perennials ,namely :

Uprigh t Buttercup (Ranuncu lus acri s) , Bu lbous Crowfoot (R .

bulbosus) , Jack-by-the-H edge (S i symbrium Alli ari a) , Mouse-ear

Chi ckweed (Cerastium trivi ale) , R est -h arrow (Onon i s arvensi s) ,Meadow P ea (Lathy rus pratensi s) , Tormentil (P otenti lla erecta) ,Lady ’

s Mantle (Alchemi lla vulgari s) , Burnets (P oter ium S angu i sorba

and P . ofli cinale) , Earth -nut (Conopodium majus) , Beaked P arsley(Anthri scus sy lvestri s) , Wild Carrot (Daucus Carota) , Yellow B ed

straw (Galium verum) , Field S cabious (S cabi osa arvensi s) , Daisy(B elli s perenni s) , Yarrow (Achi llea M i llefolium) , Ox -eye Daisy(Chry santhemum Leucanthemum) , Ragwort (S eneci o jacobaea) ,Knapweed (Centaurea n igra) , Great Knapweed (Centaurea S cabi osa) ,Cat’s-ear (Hypochaeri s radi cata) , Au tumn H awk—bit (Leontodonautumnale) , Dand elion (Taraxacum ofi

‘icinale) , Cowslip (P r imula

veri s) , Germander Speedwell ( Veron i ca Chamaedrys) , S elf-H eal

(P runella vulgari s ) , H oary P lantain (P lantago medi a) , R ibwortP lantain (P . lanceolata) , S orrel or Green Sauce (Rumex Acetosa ) ,Field Rush (Lu zu la campestr i s) , Spring Sedge (Carex caryophy llea ) ,Yorksh ire Fog (H olcus lanatus ) .

We thus see that for a weed to succeed among the turfforming plants of meadows and pastures it must possess

a S imilar mode of vegetative growth and reproduction , andbe a perennial . Very few annuals succeed here, and ofthese the most successfu l are root -paras ites , such as the

Eyebright and Yellow Rattle . But arable land , regularlydisturbed and prepared for the cultivation of annual and

biennial crops , is well adapted to the requ irements of annual

weeds .

CHAPTER XXX I I I

VEGETATION OF THE SEA COAST

A GLANCE at a geological map of Britain shows , not onlyhow Varied are the rocks inland , but also how varied they

are along the coast . Further , just as large inland areas are

covered by superficial deposits of ice-borne materials such

VEGETATION OF THE SEA-COAST 38 1

as clay, sand , and boulders , obscuring the solid rocks be

neath , so along the coast,thick beds of such materials may

be found , somet imes forming high , easily—denuded cli ffs .

Steep rocks offer a jagged resistant line to the tearing action

of the waves , and are covered with Spray at every high t ide .

At the other extreme , low ground may pass graduallyseawards and deaden the force of the incoming waves .

The varied materials of the coast are exposed to the cease

less efforts of the sea and atmospheric weathering ,and the

products of denudation are spread out in a characteristic

manner along the coast , and form a somewhat unstable soilfor plants . In some places it is finely pulverized and

muddy, in others it is coarser and sandy, and heaped up

into banks or dunes or the st i ll coarser pebbles and bou ldersmay form banks of shingle . The coast -line thus offersa great variety of surface and so il , and we might expect

the influence of these variations to be reflected on the coast

vegetation . But the factor which most powerfully influences plant - life along the coast i s the presence of salt water ,and the plants exposed to its influence show many peculiarit ies both in colour, form , and structure .

In consequence of these conditions , which of necessity

are confined to a narrow belt around the coast , we find

certain types of vegetation which present a strong contrastto the vegetation immediately beyond it . The best -marked

plant-format ions of the coast are those of the sand-dunes

and salt -marshes , the vegetation of which impresses us at

once by it s peculiar , blue-grey colour .S eaweeds .

— In the sea , or along that par t of the coast

Often covered by sea—water , seaweeds abound . If thecoast i s rocky, brown seaweeds , like the Bladder—wrack and

other Species of Fucus and P elvetia,often form a long belt ,

the plants being anchored to the rocks or to stones bypeculiar holdfasts . Farther seawards are the light , yellow

brown straps of Laminaria and in the rock-pools and in

382 ECOLOGY

parts always covered by sea-water are numerous red

seaweeds . All these are Algae , a group of plants ofmuchmore lowly organization than the flowering plants , and

differi ng widely from the latter in not having true roots ,stems , or leaves , and producing no seeds .

S alt-marshes .

—Between the t ide—marks is a belt destituteof vegetat ion here the ground is regularly under the influ

ence of the waves . If we listen to the roar of sand and

pebbles as the waves roll inwards and retreat , and watchthe constant movement of the surface

, we can realize howdiff icu lt it is for plants to secure a root -hold in such unstableground . In areas where the ground is bare for longerintervals, as along the Shores of Sheltered bays

,in estuari es ,

or the banks of t idal rivers , land-plants establish themselves .

The muddy soi l which accumu lates in such localit iesprovides a peculiar habitat for plants . It is badly aerated,liable to be covered by sea-water at very high t ides , andthere is often much salt in the ground-water . On the other

hand , during exposed intervals ,much evaporation may takeplace , leading to a concentrat ion of salt in the soi l . Or the

reverse i s possible during heavy rains much salt may be

washed out of the soil . Under such conditions it is notsurpri sing to find the ground occupied by a peculiar type ofvegetat ion .

A habitat of this kind is known as a salt-marsh (Fig .

The plants growing here have usually fleshy leaves covered

with a waxy bloom or grey hairs ; some develop shorthairs which break off and form a mealy covering over the

surface . Most salt -marsh plants have a reduced transpiringsurface , and store water in their fleshy t issues . They thus

possessmany of the characterist ics of xerophytes ; some of

them, however , e . g . the Glassworts (Sali cornia spp. ) andSea Aster (Aster Tripolium) , transpire freely, and are evenable to absorb water by their green surface . Salt -marshplants are known as h alophy tes .

FIG . 247 . OLDE R SAND - DUNEs .

— In th e foreground DwarfWillowsin th e centre i s seen th e invasion by Marram-

grass .

FIG . 248 . TRANS VE RS E SECTION OF LEAF OF MARRAM -GRAss .

VEGETATION OF THE SEA-COAST 383

The plant best able to withstand salt water is the Glasswort (S ali corni a) , which acts as a pioneer, but near the sea

the plants are few and occur only at wi de intervals . The

Grasswrack (Z ostera marina) often occurs in quantity, and

is interesting in that it flowers under water , and has pollengrai ns which float in and are carri ed by water from the

anthers to the stigmas . Other plant s generally met withon the salt—marsh are the following : Sea Poa (Glyceria

mari tima) , Sea Arrow—grass (Triglochin maritimum) , SeaAster (Aster Tripolium) , Glasswort (S ali cornia radi cans) ,Sea Oraches (Atriplex Sea Purslane (A . portulacoides) ,Sea Spurrey (Spergularia mari tima) , Sea Lavender (Limonium vulgare) , Sea P lantain (P lantago mari tima) , Sea Blite

(Suaeda mari tima) , Scurvy-grass (Cochlearia ofii cinali s)and other species , e . g . Cochlearia angli ca Sea Rush

(Juncus mari timus) , Sea Milkwort (Glauxmari tima) , Buck’

s

horn P lantain (P lantago Coronopus) , Sea Couch- grass

(Agropyron pungens) .These species vary much in d istribution with the nature

of the ground , as to whether it i s muddy or sandy low

lying and wet or raised , exposed , and drier . The associa

t ions of plants occurring in these di fferent part s of the saltmarsh , together constitute the salt -marsh formati on .

Rock-plantsl— Many of these plant s occur also on the

rocks of the coast , especially those washed by the spray.

The more characteristic are : Samphire (Cri thmum mari

timum) , Sea Lavender (Limonium vulgare) , Buck’s-horn

P lantain (P lantago Coronopus) , Sea P ink (S tati cemari tima) ,and Sea Campion (S i lene mari tima) .Sand-dunes .

— If we examine the sand along the shorewhich is subj ected to the action of the waves, characteri sticripples will be found on the surface ; but , in addition towave-ripples , other similar ripples may be seen , especially

on sand over which wind has blown for a few hours The

wind rolls the sand -

grains before it and heaps them up in

384 ECOLOGY

li ttle ridges the windward slope of each ripple is gradual,but the lee side is steep (Fig . If we watch the ripplesduring high winds we can see them shift thei r position the

sand is blown up the gentler slope to the crest of the ridge ,

then rolls down the leeward slope where it i s protectedagainst the wind and is likely to lodge . Thus , while thewindward Slope i s wearing away, accumu lation is going onon the leeward side . In this way the little ri pples movesteadily forwards in the direction in which the wind is

travelling. If in its progress a plant (or even a pebble) isencountered , a little heap of sand i s bui lt up around it , andi t may eventually be buried . If , however , the plant by

continued growth is able to keep it s tip above the surface ,

themound may increase in size and form a min iature sanddune . It i s in this way that sand-dunes are built up ,

and

they are thus the resu lt of two causes : (1 ) the action ofwind on mobile sand , and (2) the binding action of plantswhich establish themselves on the sand so transported .

The plant which is best able to overcome the difficultiesof shifting sand is the Marram-

grass (P samma arenaria) ,which

,by Vi rtue of its long perennial rhizomes and deep

growing fibrous roots,helps to bind the sand together ,

while it s shoots , by being able to grow and keep above thesurface, not only maintain the exi stence of the plant , but

aid considerably in bu ilding up the dune . By the decayof the older parts of the plants , humu s is added to the soil,so that the Marram-grass becomes a valuable pioneer o f

coast-vegetation . As we have seen (p . the vegetative

mode of reproduction of this plant i s put to pract ical usealong miles of our coasts as a

‘ land—winner (Figs . 247 ,

80,and

The windward side of a dune i s usually bare (Fig .

but on the crest are the Marram-

grass and Sea Lyme-

g rass ,which not only serve as sand-binders but provide protectionand a suitable soi l for other species . On the more sheltered

386 ECOLOGY

probably derived from internal dew in the sand . The

plants able to withstand salting and to endure the severeconditions along the shore are few In number and for the

most part xerOphytes ,with tough , leathery, rolled or reducedleaves (Fig . In some the leaves are fleshy and oftencoated with wax,

others are spiny ,and plants with branch

Sp ines are not uncommon . Grey-

green is the prevailingcolour of the vegetation .

The names shifting dunes travelling dunes grey

dunes and white dunes by which sand-hills are com

monly known , are suggestive of their most characteristic

features . Beyond the shifting dunes , and farther fromthe influence of mobile sand

,a grassy vegetation develops,

which forms a sod,covering and protecting the sand . The

dunes are low,the sand is more firmly fixed , and contains

more humu s there is greater variety of soil and surface , and

in consequence a much more varied flora is supported .

On the one hand are the dry sand-banks with their grey

green xerophytes , and on the other , wet hollows supporting

a marsh vegetation . To this part of the coast the namefixed dune is given nevertheless , the area is liable to becovered during high winds by blown sand , and this has aninfluence on the character of the vegetation . Cu ltivated

crops farther inland often suffer materially from the effectsOf blown sand . The dominant plants of the fixed dune areSand- sedge (Carex arenari a) , Fescue—grass (F estuca rubra

var . arenaria) , and sometimes Sea Couch -

grass (Agropy ronjunceum) . Associated with these and sometimes abundantare Sea Cat ’s- tai l—grass (P hleum arenarium) , Rest -harrow

(Ononi s repens) , S tork’s-bill (Erodium ci cutarium) , B ird

’sfoot Trefoil (Lotus corni culatus) , together with Speciesoccurring on the shifting dunes , and numerous Specieswhich havemigrated from adj acent pastures and meadows .In places

,bushes are so abundant as to form thickets , e . g .

Dwarf Willow (S alix repens) , Sea Buckthorn (H ippophae

FIG . 2 49 . A SHINGLE BEACH INVADED B Y ORACHE AND SALTWORT .

FIG . 2 50 . COTTON-GRAS S MOOR .— S ingle -h eaded Cotton-

grass in fru it .

388 ECOLOGY

and covered at high tides by the waves , it is devoid ofvegetation , and , lik

’

e the sand between tide-marks , theshingle is moved to and fro freely by the advancing and

retreating tides . On such a Shifting surface, plants cannotgrow . Even in larger banks , and when the crest is beyondthe reach of the highest tides , the shingle is more or lessmobile by reason of the heavy impact of the waves and the

readiness with which the sea-water percolates and buoysup the loose materials of which the bank is composed .

The shingle bank has a steep seaward S lope , and a more

gradual landward slope. On the seaward Slope very fewplants occur, and the general appearance is that of a bare

bank of rounded stones . The bank is apparently dry, butif a few of the stones are examined they will be found

to be wet even in very dry seasons , and often covered

with lichens . The water, too ,is fresh , not sal t . Drifted

materials, such as seaweed and animal—remains carried up

by the waves , especially during storms , accumulate between

the stones and form a black soil on which flowering plants

from neighbouring ground can establish themselves and

form an open association .

Shingle-binding plants .

— Before a plant—covering is possible

,the mobile beach has to be rendered more stable,

and$

several species of plants do great work as pioneers

and shingle-binders , e . g . the shrubby Sea Blite (Suaedafruti cosa) , Sea Campion (S i lene mari tima) , and the Sea

Purslane (Arenaria peploides) . As with sand-binders , theessential character required is the power of the plant togrow through the Shingle and regain the surface when

buried, and the shrubby Sea Blite possesses this power in

a remarkable degree. The plant , when grown on stable

ground , is much branched , three to four feet high ,and has

a stem an inch or more in thickness the leaves are small

and fleshy and covered with a waxy bloom . On mobile

Shingle,however

,the young plants quickly anchor them

VEGETATION OF THE SEA-COAST 389

selves by means of long roots,and produce stems , at first

erect , but which are Soon laid prostrate by shingle rolledover them by the waves . From the horizontal branches ,new erect shoots arise and grow above the surface these

in turn are bent over and covered , and so the process is

repeated . The plant , thus growing along the line of the

moving shingle,travels obliquely to the crest of the bank ,

where it establishes i tself . From the prostrate stems ,a tangle of adventi tious roots arises , which ,

together wi ththe mat of shoots

,serves to prevent the removal of shingle

as the water runs down the bank . Further, the shootsarrest the landward flow of shi ngle , and the crest becomes

raised beyond the reach of the highest tides ; thus a sea

wall i s formed which effectually checks the force of the

waves . The Sea Blite,therefore

,may , by its vegetative

growth and power of rejuvenescence ,become a valuable

protector of the land against the incursions of the sea .

Some of the plants on the shingle beach are halophytes ,e . g . the Oraches and Beet , Sea Blite , and Sea Campion ,

which are able to grow in parts influenced by the salt water .

Others are characteristic of sand -dunes , especially if the

beach has been formed on a bed of sand , e . g . Sea Purslane ,Horned Poppy (Glaucium luteum) , Biting Stonecrop (S edumacre) , Viper

’s Bugloss (Echium vulgare) , and Sea P ea (Lathyrus mari timus) or strand-plants , e . g . the Saltwort (SalsolaKali ) . Frequently plants from the neighbouring fields andcultivated ground occur, their seeds having been carriedto the beach by the wind or by birds , e . g . Elder (Sambucus nigra) , Woody Nightshade (S olanum Dulcamara var .

marinum) , Curled Dock (Rumex cri spus) , Creeping Buttercup (Ranunculus repens) , Herb Robert (Geranium Rober

tianium var . purpureum) . On themore sheltered and stablelandward slope of the beach ,

plants are more abundant , andthei r remains form a humus on which eventual ly a grassy

carpet may form . In this way the open association of the

390 ECOLOGY

shingle beach may be replaced by a closed associationof pasture Species .The conditions chiefly affecting plant—life on the coas t

are mobile soil and salt water . On the disturbed groundthe plants are usually annual s anchorage is secured bydeep—growing tap - roots , and the long rhizomes and numerousadventitious roots of perennials serve as binders for theloose soil . The Shoots are liable to be buried , but thei r

great power of rejuvenescence enables them to keep above

the surface and ai d in bu ilding up banks of sand and shingle .

The plants have usually a low habit,whereby the tearing

effect of the wind is reduced . The shoots are modified in

many ways : the stems and leaves may be Spiny ; the

leaves are often small or reduced by rolling fleshy plantsare common

,and the epidermis is covered by a grey waxy

bloom or by hairs . In some species the hai rs become

detached and form a meal ’ on the surface . By such

modifications the stomata are protected ,transpiration and

radi ation reduced,and the water-supply conserved . P lants

possessing these modifications are able to survive the con

d itions of the habitat,and they give a characterist ic

appearance to the vegetation of the coast .

CHAPTER XXXIV

MOORLAND AND ALP INE PLANTS

MANY of our Englishmoorlands occupy the sites of former

woodl and or scrub ,and are extens ively developed on the

Pennines and on the Cleveland Hills . Two distinct types

occu r ( 1 ) the Cotton-

grass moor (Fig . 25 0 ) and (2 ) theHeather moor (Fig . 25 1 ) but these are connected by severalintermediate phases or t ransition types .

MOORLAND AND ALP INE PLANTS 391

Cotton-

grass moors .-A large part of the Pennine plateau

is covered with deep,very wet , acid peat , which contains

much organic matter and is very poor in mineral salts . It iscomposed of the remains of previous generations of Cotton

grass and othermoorland plants , and ,in places

,of Bog-moss

and Hai r-moss,while buri ed at the base of it are numerous

remains of B irch and other trees . Growing on this is amonotonous stretch

, manymiles in extent , of Closely packed

tussocks or hassocks ’

of the Cotton -grass ; its growthbeing favoured by a high rainfall of 45 inches or more .

Locally these Cotton -grass areas are called mosses and

very many place-names are derived from them.

Very few other plants are found here the chief are theCloudberry

,Crowberry (Fig. 253 , r ) , and Bilberry (Fig . 254 ,

Here and there are patches of Bog-moss,growing over

which are the slender branches of the Cranberry (Fig . 254,

Two species of Cotton-grass are met with .

’

One ,by far

the more abundant (Fig . has narrow leaves permeated by two rows of large air- channels (Fig . 255 , and

when in fruit , bears a single cottony tassel . The other kind ,

Often confined to wet channels or hollows , has broader leavesand large ai r-spaces (Fig . 255 ,

and bears several cottonytassels on its fruiting Shoot (Fig . 1 58, r ) . The stomata

in both species are on the exposed surfaces and this

feature , together with the large air-channels,recalls struc

tures we have met with in water-plants . Another point

of comparison is that the Cotton -grasses grow in a wet ,

badly aerated soil , very rich in organic matter .

At the edges of the Cotton -grass moors , Where drainage is

better and the peat drier and shal lower , the Cotton-gras ses

are replaced by Bilberry (Vaccinium Myrti llus ) , and with it ,but growing less abundantly ,

are Cowberry (V . Vi tis -Idaea) ,

Crowberry (Empetrum nigrum) , and other heath-plants .

Often long Bilberry edges thus arise (Fig . On the

s teeper, more sheltered slopes , extensive stretches of

392 ECOLOGY

FIG . 2 5 3 . HEATHS AND H EATH-LIKE MOORLAND P LANTS W ITHBACK-ROLLED LEAVE S .

-I , Crowberry ; 2, Ling ; 3 , Cross- leaved

H eath ; 4 , Fine- leaved H eath ; a , leafy shoot ; b,transverse

section o f leaf ; 0 , fru iting branch ; d , male flower ; e, female

flower ; f , fru it from below g, fruit cut open to Show the seeds

h , section of leaf of Ling i , section of leaf of Cross-leaved Heath .

394 ECOLOGY

becoming rus ty brown in the autumn . The Heather moorsare a lighter green in summer assuming a rich pu rpletowards autumn , when the plants are in flower . This isa region of dwarf evergreen Shrubs

,the dominant species

being the Ling (Fig . 2 53 ,

The peat of the Heather moor is shallow, Often sandy ,

and acid , and is frequently developed over sandstones or

other areas with a Shallow, well—drai ned siliceous soil but

Heather moors a lso occur, as we have seen ,over limestone .

At the base of the peat is often found a hard gritty layer

called the moor pan consisting of sand-grains bound

FIG . 2 5 5 . SECTIONS OF UP -ROLLED LEAV E S OF MOORLAND GRAS SEsAND SEDGEs .

—I,Tu fted H air-grass ; 2

,Sh eep ’

s Fescue-

grass3 ,Mat -grass ; 4 , Waved H air-grass ; 5 , Many-h eaded Cotton

grass ; 6 , S ingle-h eaded Cotton-grass ; a , air-spaces .

together into a compact bed , a few inches in thickness , by

ei ther oxide of iron or humus—compounds . This pan isoften so hard that roots of young trees cannot penetrate it .

The plants found on heaths have many featu res in com

mon . The Shrubs,with the exception of the Bilberry

,are

all evergreen,with greatly reduced ,

back- rolled leaves , asShown in Fig . 253 . An interest ing series comprises Cow

berry (Fig . 254,2 ) with edges S lightly curled back, Cranberry

(Fi g . 2 54 ,and Cross - leaved and Fine- leaved Heaths

(Eri ca Tetralix and E farther back—rolled (Fig . 253 ,

MOORLAND AND ALP INE PLANTS 395

3 and In the Crowberry (Fig . 253 ,r ) the hai ry edges

meet , while the Ling has the Smal lest leaf, and its undersurface is confined to a narrow groove . In all these Casesthe stomata occur only on the under surface.

The Bilberry (Fig . 254 ,1 ) usually sheds its leaves in the

autumn ,but i ts bri ght-green angular stems (Fig . 254 , a , b, c)

render i t functionally evergreen . Small stunted forms ,however

,of the B ilberry retain thei r leaves through the

winter . The B ilberry is able to withstand great extremesi t ascends to a greater alti tude than the other species , and

is frequently the dominant plant on high , exposed , rocky

summits .

Moorland grasses have also rolled leaves (Fig . 25

Along thei r upper surfaces are ridges , between which are

lines of large,watercontaining cells . When water is

abundant and these cells are distended ,the blade spreads

out but in times of drought,water is withdrawn from the

cells , the ridges in consequence fall together , and so the bladerolls up . In the grasses , therefore, the blades are up

- rolled ,

and not,as in the heaths , back-rolled . In the grasses , too ,

the s tomata are on the sides of the ridges on the upper

surface, and are absent from the lower more exposed sur

face,which is protected by a thick cuticle . In ei ther case

the rolled leaf encloses a chamber of still air, and as the

stomata are in this,they give off very little water . In

these ways plants are well adapted to withstand the severeconditions of life on the moors .

The water- logged , acid peat decomposes very slowly, andthemineral substances i t contai ns are not readi ly avai lablefor plant- food . Peat-plants , however, agree in one respect

with those growing in humus they are able to subsis t by

the aid of mycorhiza , which is present on the roots of most

moorland plants .A plant often abundant on Heather moors and on moun

tain slopes is the Gorse or Whi n (Figs . 1 32 and and

it exhibits many interesting modifications which should be

396 ECOLOGY

carefully studied . What is the nature of the Short spines

Where and how do they arise D istinguish between leaves ,

and branches . Cut a section across the stem ,and note how

much the ridges . on it increase the green , assimilating sur

face- tissues (Fig. 256 ,Seedlings may eas ily be grown ,and the history of the leavesand spines determined (2 andThe cotyledons (2 , 3 , 4 , c) are

entire,but the first foliage

leaves (d) are trifoliate . AS the

plant grows , the newer leavestend to produce smaller lateralleaflets

, and eventually the

centre leaflet only is produced ,and this is very narrow and

sharp pointed , but flexible .

Buds arising in the leaf—axils

grow into shoots with narrow ,

undivided , and sharply- pointedleaves , and the branches alsobe

come Sharply po inted , harden ,

and so form a branch—spine .

Fm 2 56 . GORS E SEED The development of trifoliate

LINGS .

— I, transverse section leaves in the seedl ings suggests

Of S tems ? 2 , Young “flaming ? that the Gorse has probably

310mm seedhng ’4 ’ d lfi el ent descended from an ancestorki nds of leaves on a seedhng ;

c , cotyledon d to i , transition wi th compound leaves , wh l chfrom trifoliate leaf to need le nOW only persist in the seedl ingleaf ; m’

rOOt ' tuberd eS ° stage . We have al ready noticedthe interesting way in which

seeds of the Gorse are dispersed by ants (p . 226, Fig .

The Sphagnum bog— The Sphagnum bog is dominated

by species of Bog-moss (Sphagnum) and other peat-formingmosses such as the Hai r-moss (P oly tri chum) . It is developed on an impervious soil in situations where the air isvery moist , ei ther at low or high levels and an essential

398 ECOLOGY

grasses and sedges (Fig . or back-rolled as in heaths

(Fig . with s tomata sunk in pits or grooves . The

blades are usually small,leathery

,hai ry or fleshy

,and often

arranged in compact rosettes , form ing the cushions so

famil iar in rockery plants like the Saxifrages (Fig .

Houseleeks, Cushion P inks (S i lene acauli s) , or the woolly

leaves and flowering Shoots of Edelweiss (L . alp inum) .Some plants form dense mats of interlacing trailing stems .

Such are the procumbent Azalea, Crowberry (Fig . 253 ,

Alpine Club MOSS (Ly copodium alp inum) , the dwarf form s ofBilberry

,and Alpine Willows . These form a flat carpet

with their numerous rhizomes matted in the soil . Sectionsof the Willow-stem may Show many (from fifteen to

twenty) annual rings , but in spite of thei r age the plantsonly grow a few inches from the ground.

Insects are scarce,and usually of the lower types yet

many alpine plants produce large ,showy flowers like the

P inks,Saxifrages

,and Gentians . Vegetative reproduction

by means of Offsets , runners , and rhizomes is prevalent .Vivi parous plants (see p . 1 41 ) are not uncommon on the

mountains . Examples are Sheep’s Fescue (F estuca ovina) ,Alpine Poa (P oa alp ina) , Alpine Bistort , and some sedges .

The study of plants and their distribution reveals the

great power of adaptation which they possess . In relationto the factors of the envi ronment

,plant- organs are modified

in a great variety of ways and present remarkable contrastsin form and structure

,e . g . water-plants and plants of the

sea- coas t or the Heather moor plants of the mois t,shady

woodland and the dry,sunny desert t rees of the lowland

forest and the flowery cushions of themountains . Our knowledge of the conditions under which these varied forms grow ,

leads us to conclude that the mai n features of the vegetationof a country are determined by the condi tions of the habi tat .The plants of a given associat ion ,

however , react on the

habitat , and ,by changing th e condit ions of the hab itat ,

prepare the way for new forms and the extinction of the

FIG . 2 57 . A CUSHION OF SAXIFRAGE .

APPEND IX

EXAMINATION PAPERS

UNIVERS ITY OF OXFORD

LOCA L EXAM INATIONS,JULY 1 9 1 2

S eni or

I.Describe conci sely th e spec imen provided. $In describing

an inflorescence or flower, cand idates should i llustrate th e

relat ive posit ions of th e various parts both by a hori zontaland by a vertical plan ]

2 . S tate briefly h ow th e presence of starch in green leavesand in underground stems i s to be explained .

3 . Wh at spec ial structures are found in th e wood of a

D icotyledon ? Explain h ow th e form and nature Of thesestructures fits them to carry on their special work .

4 . Describe th e mode of pollinat ion a nd th e relat ion of

th e parts of th e flower in two o f th e following : Willow ,

Deadnett le ,Evening P rimrose ,

Sunflower .5 . Three leaves of an ind ia - rubber plant are cut Off , and

vasel ine i s rubbed on th e under surface of one , on th e uppersu rface of another, and on both surfaces of a th ird . Th ey arethen left for a week, hanging in air . S tate th e result in each case .

Give a brief explanat ion and an account of th e physiological

process concerned .

6 . Describe briefly th e Characterist ic fruits of Cruc iferae ,

S crophulariaceae , and Labiatae . Describe in one case th emode

of seed -d ispersal .

7 . Give an account of th e vegetat ion to be found in a cornfield

,or a sh ingle beach, or a sandy heath . Ment ion six

characterist ic plants from th e situat ion you select .

APPENDIX 40 1

8 . Describe three methods of vegetat ive reproduct ionamong flowering plants , giving examples of each case . What areth e advantages and d isadvantages of th is method as comparedwith reproduct ion by seeds

9 . G ive an account of th e structure (om itt ing microscopicaldetails) and s ituat ion on th e tree of th e male and female conesOf a P ine . H ow i s pollinat ion brought about in the plant


LOCAL EXAM INAT IONS , jULY 1 9 1 1

belonging to th e Labiatae .

I O . Explain why it i s that leaves are usually green , thin ,

and flat.


LOCAL EXAM INAT IONS , J ULY 1 9 1 1

P reliminary

I . Describe th e flower of ei ther th e Buttercup , or the P ea,

or th e Wild Rose . S tate, as far as you can ,th e uses of th e

various parts .

l 2$6

APPEND IX

EXAMINATION PAPERS

UNIVERSITY OF . OXFORD

Grateful acknowledgement is made of the permiss i ons

which have been g iven by the Univers ities and other bodies

under whose authority the examination papers here printed

w ere set.

1 296 Woodhead ’s S tudy of P lants To f acep. 4 0 1

5 .

“

Th ree leaves'

OI an Ind iai ru b be‘

r'

p lant are cut off , and

vaseline i s rubbed on th e under surface Of one , on th e uppersu rface of another, and on both surfaces of a th ird . They arethen left for a week, hanging in ai r . S tate the result in each case .

Give a brief explanat ion and an account of th e physiological

process concerned .

6 . Describe briefly th e characterist ic fru its of Cruciferae ,

S crophulariaceae , and Labiatae . Describe in one case th e mode

of seed - d ispersal .

7 . Give an account of the vegetat ion to be found in a cornfield , or a sh ingle beach, or a sandy heath. Ment ion six

characterist ic plants from th e situat ion you select .

40 2 EXAMINATION PAPERS

2 . What i s th e use of th e fru it to a plant ? Make drawingsof two fruits whi ch you have examined and name th e d iff erent

parts .

3 . Wh y does a plant spread its leaves to th e light and air

Describe two experiments you have seen whi ch prove what

you say .

4 . Describe fully h ow Daisy plants spread over a lawn .

5 . Describe a seed , and say what changes you would see

as it grows into a young plant .6 . Describe any winter—bud whi ch you have examined .

What becomes of th e d iff erent parts in Spring

UNIVERSITY OF CAM BRIDGELOCAL EXAM INAT IONS ,

DEC . 1 9 1 I

S enior . A

A I . Write a conc ise descript ion of th e specimen M $=B ouvardi a] . Show by means of sketches th e relat ive posit ionsof th e parts of th e flower and draw attent ion to any characterswhi ch have spec ial reference to i ts method of pollination .

A 2 . Describe some simple experiments to illustrate th e

effect of light on th e growth and development of a green plant .A 3 . What do you understand by vegetat ive propagat ion ?

Give three examples of structures spec ially adapted for th ispurpose .

A 4 . With what habitats would you assoc iate any four ofth e following Gorse, S tone-crop

,Dandel ion

,Wh ortleberry

(or B ilberry) , Sundew , Cleavers (or Goose-

grass) Ment ion anycharacters of th e plants selected which you m ight regard asdeveloped in relat ion to their respect ive habitats . (Cand idatesnot in th e United K ingdom may ,

i f they wi sh, substitute thefollowi ng quest ion for quest ion A 4

Ment ion th ree climbing plants , and give some account ofth e means by whi ch they ga in th e requ ired support . )

B

B I . Write a botanical account of th e spec imen N $=Acaciaseed ling] . Expla in , so far as you are able , any notable

peculiarities .

APPENDIX 40 3

B 2 . Describe with th e aid of sketches th e form and arrangement of th e parts of th eflower of (a) a Buttercup , (b) aWild Rose ,

and point out th e chi ef d iff erences between the two . (Cand idates at centres not in th e United K ingdom may ,

i f they wish,subst itute the following quest ion for question B 2

Describe w ith the aid of sketches the form and arrangementof parts of some papilionaceous flower, and suggest th e

method by whi ch pollinat ion is effected . )B 3 . Give Some account of th e phenomenon of leaf-fall and

th e changes in th e leaf whi ch precede its occurrence .

B 4 . Describe th e structure of th e seed of some monocotyle

donous plant (e . g . Wheat) , and give some account of th e

changes wh ich take place in it during germination .

UNIVERS ITY OF CAMBRIDGE

LOCAL EXAM INAT IONS ,DEC . 1 9 1 1

junior

I . Make labelled d iagrams to illustrate th e structure of

specimen K bud of Brussels Sprouts] and its parts .

2 . D issect specimen L fru it of Acer] and describe its

structure by means of labelled d raw ings . Ment ion in a few

sentences any po ints Of biological interest whi ch strike you .

3 . Why do grasses flourish, although they are closelycropped by grazing animals Expla in h ow it is that grassesmake a firm soft turf and why th e grass on a lawn should bekep t short .4 . Give some account of th e ways in whi ch plants are

adap ted to take full advantage of th e light which falls uponthem .

5 . Some trees are evergreen , others for part of th e year areleafless . Ment ion one tree of each k ind , and explain as far

as you can th e meaning of these d ifferent habits .

6 . What i s a stoma ? In what important funct ions do

stomata play a part

C C 2


7 . Name four dehiscent fruits , and describe in each case

h ow th e seeds are enabled to escape .

8 . H ow do water-plants Obtain their food

UNIVERSITY OF CAMBR IDGE

LOCAL EXAM INAT IONS , DEC . 1 9 1 I

P reliminary

1 . Describe an experiment which shows that water i s givenOff from th e leaves of a plant during a warm day . F rom whatsource i s thi s water obtained , and how i s it carried to th e

leaves2 . Give two examples of plants which accumulate largereserves o f food at some period of the ir lives . Wh at is th eadvantage of these stores of food to th e plants concerned

3 . What are th e ch ief d ifferences in external featuresbetween roots and stems ? Name a plant whi ch has an

underground stem .

4 . Describe briefly th e parts of some brightly coloured

flower . Give th e name of th e flower, and sta te prec isely th efunct ions o f th e parts you describe .

5 . Describe as fully as you can th e appearance presented byth e surface of th e stump of a tree after th e trunk h as beencut down .

6 . Th e root of a plant grows downwards and the shoot

grows upwards . Explain th e importance of these facts inth e life of th e plant .

UNIVERS ITY OF LONDON

MATRICULAT ION EXAM INAT ION , SEP T . 1 9 I I

I . Draw a floral d iagram and a median, longitud inal

sect ion (on a large scale and showing only th e parts cut ) ofth e flower A provided , nam ing th e d ifferent organs . In bothcases th e structure o f th e ovary should be included . Referth e plant to its natural order, giving your reasons .


BOARD OF EDUCATION TEACHERS’

PRELIMINARYCERTIFICATE

EXAM INAT ION , AP RIL 1 9 1 1

Special S ection C . Botany

7 . Describe care fully th e structure of th e flower of the

Orchi s , V iolet , or Dandelion. Make a drawing of a longitud inalsect ion of th e flower to show clearly th e position of th e variousparts , and draw th e floral d iagram .

8 . Compare th e structure o f th e corm of a Crocus with thatof th e bulb of a H yac inth, and Show ,

with th e ai d of sketches ,how new corms and bulbs are found on th e old ones .

9 . Draw and describe a leaf of Ivy and compare it witha leaf of P rimrose . Explain any obvi ous po ints of structurald ifference with reference to th e habit of th e plant and its

environment .1 0 . A stone lying in a field is removed and the grass beneath

is found to be d iscoloured . Account for this , and describeexperiments to Show what effect the cond it ions which produced iscolorat ion may have upon th e growth of the plant .I I . Describe, with th e aid of d iagrams, th e structures

likely to be found upon a branch of H orse-Chestnut in May and

June .

1 2 . What cond it ions affect th e rate of transpirat ion inplants ? Describe any experiment whi ch may be made to

determine th e rate of transpirat ion under various cond it ions ,and sketch th e apparatus used .

BOARD OF EDUCATION TEACHERS’

PRELIMINARYCERTIFICATE

EXAM INAT ION, MARCH 1 9 1 2

Special S ection C . Botany

7 . Describe, with th e aid of sketches , the two kinds of

flowers which are to be found on V iolet plants . Whatexplanat ion can be given of th e presence of these two kindsof flowers

APPENDIX 46 7

8 . How do plants ob tain their food and in what form ?

S tate clearly th e experimental evidence upon which yourstatements are based .

9 . Give an account of th e l ife-hi story of th e P otato , and showclearly , with th e aid of sketches , on what part of th e plantth e tubers are formed . Describe th e structure of th e P otatotuber .

1 0 . What experiments could you devise to show how th e

rate of transpirat ion of water from a leafy plant compareswith th e rate of absorpt ion of water by its roots Upon whatex ternal cond it ions does th e act ivity of transpirat ion dependI 1 . Describe some of th e common methods by whi ch weeds

are spread . I llustrate your answer by description of threespec ific instances of d if ferent methods .

1 2 . Describe th e structure of th e flowers in two plantswhi ch are cross-

pollinated by th e wind , and in two plan ts wh ichare cross- pollinated by insects . S tate clearly what experi

mental evidence there is for th e statement that , in many cases ,cross-pollinat ion is more effect ive than self—pollinat ion in th eproduct ion of seeds .

BOARD OF EDUCATION TEACHERS ’

CERTIF ICATE

EXAM INATION, NOV . 1 9 1 1

Speci al S ecti on C . B otany

7 . On cutt ing across th e stem of a plant , such as th e Sun

flower, Begonia ,Or P elargonium , it i s found , a fter a short time ,

that water exudes from th e cut end of that part of th e stemwhich remains attached to th e root . Account so far as you

can for thi s phenomenon, and describe any experiment whichwill throw l ight upon it .8 . Wh at i s meant by vegetat ive reproduct ion in plants

Give examples of four d ifferent methods Of vegetat ive reproduct ion . I llustrate your answer by sketches .

9 . H ow would you demonstrate th e cond it ions wh ich determ ine th e format ion of starch in leaves

I O . Give sketches of th e leaves of any three Of th e followingGorse , Dog-Rose , Wood Sorrel , Marsh Marigold , P rimrose .

Account for any peculiarities of structure Observed .


I I . Compare th e structure of th e seeds of Mai ze, Wheat ,Oak , and Bean . Show in what respects they resemble or d ifferfrom one another. H ow would you classify these seeds inrespect of fundamental d ifferences of structure ? Give the

essent ial characterist ics of each class .

1 2 . Ment ion th e names of Brit ish plants which possess th efollowing characterist ics , giving an example in each class

(a) Foliage-leaves in pairs on short special branches .

(b) Reproduct ion by means of small buds whi ch fall offand d evelop into new plants .

(6 ) Seeds (not fru its) which are d ispersed by th e agency

of wind .

(d) Nodules on th e roots .

(e) F lowers with stamens and pistil but no calyx or

corolla .

(j) Spec ial adaptat ions of the leaves to withstand drought.

CENTRAL WELSH BOARD

ANNUAL EXAM INAT ION ,JULY 1 9 1 1

B otany

1 . Describe a typical flower . Explain th e uses of the variousparts and show h ow they are adapted to fulfil their funct ions.

2 . What part of a flower i s a fru it derived from ? Name

three kinds o f dry and th ree ki nds of succulent fru its , and

Show in each case how th e d ispersal of th e seeds i s broughtabout .

3 . Describe th e vegetat ion o f one of th e following localit ies(a) a hedge , (b) a river-side, (c) a wood .

4 . What are th e d ist inguishing characters of th e orderRosaceae ? Ment ion three wild and three cult ivated plantsbelonging to the order .

5 . Give two examples of underground stems . By whatexternal marks would you d ist inguish them from roots6 . What i s meant by respiration ? What parts of plantsrespire Why should plants not be kept in bedrooms

4I O EXAMINATION PAPERS

3 . Wh at d ifferences would you expect to find in the seed

lings of Beans whi ch have been grown respect ively underord inary cond it ions and in th e dark4 . Give some account of th e part whi ch is played in plantnutrit ion by ( 1 ) sugar, (2 ) starch .

5 . Describe how you would demonstrate experimentallyth e growth in length of a root .6 . Give some account of th e t issues whi ch are concerned in

th e transport of water in a plant .7 . Write botanical descript ions of th e spec imens A and B ;

carefully po int ing out in what ways they ( I ) resemble and

(2 ) d iff er from each other.

OXFORD AND CAMBR IDGE SCHOOLS

EXAMINATION BOARD

H IGHE R CE RT IF ICATE

(e) Special Botany

I . Give an account of th e t issues which are concerned inth e transport of water through the stemof an ord inary land

plant .2 . Wh at do you understand by photosynthesis Show

how th e form and structure of a typ ical green leaf are spec iallyadapted to thi s funct ion.

3 . Give th ree examples of mod ificat ions of th e shoot forfood -storage . Po int out in each case th e purpose of th e store .

4 . Describe with th e ai d of sketches th e spikelet of a speciesof grass , and state th e funct ion of th e various parts whi ch youdescribe .

5 . Give some account of th e methods of seed -d ispersal inth e fam ily Rosaceae . S tate prec isely what i s th e morphological nature of th e various structures to whi ch you refer.6 . E i ther Give some account of th e method of growth and

the life-hi story (exclud ing details of fertili zat ion and embryodevelopment) of Coltsfoot or S tate what you understand f by

th e term plant-associat ion, illustrat ing your answer by one

or more examples .

APPENDIX 4 1 1

7 . Write a botanical account of th e spec imen A , and d rawspec ial attent ion to any structures which bear on its methodof pollination .

OXFORD AND CAMBRIDGE SCHOOLS

EXAM INATION BOARD

E LEMENTARY F OR LOWE R CE RT IF ICATESI . Describe briefly th e funct ions of a foliage- leaf .2 . Draw a d iagram of a P otato , nam ing all th e structures

observable . Give your reasons for dec id ing whether it i sa stem- structure or a root- structure .

3 . Explain clearly th e d ifference in origin between th e ed ible

port ions of a Cherry and an Apple .

4 . Describe , w ith d iagrams , th e flower of the Buttercup .

5 . Describe , with examples , th e various methods of seed

d ispersal w ith whi ch you are acquainted .

6 . Explain why th e growth of a plant i s checked by transplant ing it carelessly .

7 . Make a careful d rawing of th e specimen provided , namingth e parts .

COLLEGE OF PRECEPTORS

CE RT IF ICATE EXAM INAT ION, CHR IS TMAS 1 9 1 1

S econd Class

1 . Describe th e spec imens before you as fully as possible .

Make d iagrams of th e floral arrangements (not drawings of th eparts of th e flowers) . Refer th e plants to their classes and

d ivis ions (not orders) , giving your reasons .

2 . Write down th e characterist ic features of th e ordersMalvaceae and P rimulaceae , and Show h ow they d iff er in th estructure of th e pistil .

3 . H ow does th e Common d iffer from th e Round - leavedMallow , and th e P rimrose from th e Cowslip Wh at i s th eimportance of these d ifferences

4 . H ow are th e d ifferent spec ies of Buttercups adapted to

l iving in (a ) th e open meadow (Ranunculus bulbosus) , (b) on

4 1 2 EXAMINATION PAPERS

mud (R . hederacens) , and (c) submerged (R . tri chophy llns) ?S tate th e meaning of th e Lat in names .

5 . What are th e funct ions of ord inary green leaves , and whyhave some plants , as th e Dodder and Broomrape (S crophularineae) , no green leaves at a ll ?


CE RT IF ICATE EXAM INAT ION, CHRI STMAS 1 9 1 1

F i rst Class . Advanced S ecti on

I . Name and describe th e flowers of th e Brit ish genera of

Corylaceae .

2 . Explain , with a d iagram , th e origin of the vascular bund lesof th e st ipules of th e Geranium and Bedstraw .

3 . When wild plants are cultivated , what are th e mostprominent effects of the change of cond it ions Give examples .

4 . Give the life-history of a Moss .


CE RTIFICATE EXAM INAT ION, CHR IS TMAS 1 9 1 1

F i rst Class . Elementary S ection

I . Describe the spec imens before you as fully as possible.

Make d iagrams (i . e . cross- sect ions) only of th e floral arrangements , and refer th e plants to their classes and d ivisions , givingyour reasons for so doing.

2 . Wha t genera of Rosaceae are cult ivated P Explain th echanges whi ch cult ivat ion h as caused in them .

3 . Give examples of roots whi ch have adapted themselvesto other purposes than that of absorbing water from th e soil .

4 . Describe any experiments in germ inat ion . Wh at do theyteach us P

5 . H ow do plants get r id of superfluous moisture , and why

6 . Describe th e anatomy , as seen in cross -sect ion , of any

ord inary root and th e uses of its several t issues .


4 . Describe th e various stages in th e opening of th e bud of

some tree .

5 . What i s respirat ion and what purpose do you suppose itserves in th e l ife of the plant P H ow would you prove that

germ inating peas respire P Wh at do you know of th e respirat ion of green leaves in th e l ight P6 . Wh at i s an insect ivorous plant ? Ment ion three nat iveinsect ivorous plants and sketch and describe one of them .

7 . Describe and compare , with careful sketches , the pollinat ion of two flowers , one of which i s pollinated by th e wind and

th e other by insects .

8 . Wh at are th e advantages and d isadvantages Of climbingas compared with th e manner of growth of ord inary plants PDescribe three d ifferent ways in whi ch plants may climb .

UNIVERS ITY OF DURHAM

MATRICULAT ION EXAM INAT ION ,SEPT . 1 9 1 1

I . Write a short account of some one flower which youhave stud ied , and explain briefly th e funct ions of its variousmembers .

2 . Describe carefully th e structure of syncarpous and

apocarpous fru its . G ive examples of some common fru itswh ich come under these heads .

3 . Explain clearly how starch i s formed in the P otato tuber,and th e source from whi ch this substance i s derived .

4 . By what experimental evidence can it be shown thata healthy shoot i s cont inually absorbing water P How i s th e

rate of absorpt ion influenced by exposure to light or darkness P5 . Contrast th e external forms of plants grown in darkness,

in shade , and in full illum inat ion .

6 . Enumerate and briefly explain the princ ipal meanswhereby plants are able to climb , and expla in th e advantageswhich accrue from a cl imbing habit .

7 . Explain clearly th e meaning of th e knots and l ines whi chare present in a deal board .

8 . Describe as fully as you can the external appearances of

th e roots of annual and biennial plants .

APPENDIX 4 1 5

UNIVER SITY OF BRISTOL

MATRICU LAT ION EXAM INAT ION, SEP T . 1 9 1 0

I . Describe fully th e specimen A provided and refer it toits natural order, giving your reasons. Annotated Sketchesshould accompany your answer .

2 . Ident ify, if possible , and d iscuss th e morphology of th e

spec imens B , C, and D .

3 . Describe as fully as you can th e course taken by waterin th e plant , from i ts entrance at th e root unt il i ts exit fromthe leaf . Describe experiments establ ishing th e truth of yourstatements.

4 . H ow does th e shape of cotyledonary leaves compare withthat of th e later leaves of plants P Can you suggest any reasonsfor th e d ifferences usually observed P

5 . Describe th e pollinat ion-mechanisms known to you as

occurring in th e natural order Liliaceae (or P rimulaceae) .6 . Describe the method of d ispersal of seeds exhi bited by

the following plants Rose ,P lane , Crane

’

s- bill, Geranium,

H ornbeam , and Campanula .

7 . In what manner could you demonstrate th e act ion of

d iastase on starch ? What physiological funct ion does th isferment (or enzyme) perform in th e leaves P8 . Describe th e Character of th e vegetat ion known to you

as frequent ing one of th e following situat ions

( 1 ) A peaty marsh.

(2 ) An old overgrown wall .(3) A sandy sea-shore .

INTERMEDIATE EDUCATION BOARD FOR IRELAND

EXAMINAT ION 1 9 1 1 (JUNE )

H onours P aper (Thi rd Year)

Sect ion A )

I . (Obligatory ) Describe th e structure of th e bulb of some

bu lbous plant . What substances does it conta in ? Where dothey come from P Wh at becomes o f them ?


2 . When do evergreens shed their leaves P Compare th eleaves of evergreens with those of dec iduous trees . Can you

suggest any reasons for th e d ifference P

3. From what sources do th e opening buds of spring drawthe ir suppl ies of material P Ment ion th e materials in each case .

4 . Describe h ow th e d iff erent regions of th e root are formed .

What are the ir uses to th e plant P Give reasons for your answer.

S ect ion B

5 . (Obligatory ) Of what uses are green leaves to plants ?Describe experiments and observat ions whi ch support youranswer .6 . Describe th e cond it ions under which seeds germinatebest . P o int out why these cond it ions are necessary .

7 . Describe th e appearance of any F ern . P o int out some

of th e chi ef d ifferences between a F ern and a flowering plant .8 . Wh at i s pollen ? Wh ere i s it formed ? What function

does it perform P


EXAM INAT ION 1 9 1 1 (JUNE )

Special P aper (Thi rd Year )

Sect ion A

I . (Obligatory ) H ow do th e following insects affect the

growth of plants : Humble-B ee , Aphi s (or green fly) , grub of

Daddy- long-legs, Wireworm ? S tate in each case what partof th e plant i s acted on by th e insect , and whether th e resultis benefic ial or injurious to th e plant .

2 . Describe th e spec ial characterist ics of grasses that inhabitsand -dunes , and show h ow these are su itable to th e cond it ionsunder which th e plants l ive .

3 . H ow can you tell th e age of th e branch of a hardwoodtree (e . g . Beech, Lime , Elm) by external and internal features PExplain how these features are produced .


3 . Descri be h ow tree trunks increase in thi ckness . As treesincrease in age what changes do th e wood and bark undergo P

4 . Give an account of th e occurrence of root-nodules on th eroots of some plants . H ow are these nodules caused , and how

do they aff ect th e l ife of th e plant P

Sect ion B5 . (Obligatory ) Describe an experiment to show that plants

exhibit root-pressure . H ow i s thi s pressure produced , and of

what advantage is it to th e plant ? Wh at natural phenomenain herbaceous plants are due to root-pressure ?6 . Describe th e method of water-culture to prove th e

essent ial inorganic food -materials requ ired by green plants .

7 . Draw th e vert ical sect ion and floral d iagram o f th e WildRose , and name th e parts of th e sect ion . Draw and describe th eleaf of th e Rose .

8 . Give examples of variet ies , hybrids , and double flowers ,and describe how each may be developed .


EXAM INAT ION 1 9 1 1 (JUNE )

Speci al P aper (F ourth Year )

Sect ion A

I . (Obligatory ) What is respirat ion P H ow may it be shownthat plants respire P Wh at i s th e use of respirat ion P

2 . H ow would you proceed to find where th e most rapid

growth in length of th e root and stem takes place P3 . Describe th e changes whi ch take place in th e endosperm

of a wheat -grain during germ inat ion .

4 . Ment ion some causes of bend ing and curvature in plants .

H ow do these causes af fect th e d ifierent parts P Describeobservations illustrating your answer .

Sect ion B5 . (Obligatory ) A square i s punched from a Sunflower

leaf before sunrise and carefully weighed . A similar square ispunched from a leaf after sunset , and its weight also recorded .

APPENDIX 4 1 9

What d ifference do you expect to find ? Suggest th e causes of

th e d ifference . H ow would you test your suggest ions ?

6 . H ow wou ld you compare th e amount of water given off

from th e leaves of a branch st ill attached to a tree , and thatfrom th e leaves of a cu t branch supplied with water P Whi chwou ld you expec t to transpire th e larger amount ? S tate fullythe reasons on which you base you r answer .

7 . H ow is it that young tender seed lings are able to stand up

r igid ly ? Why is it that this st iffness d isappears when th eseedlings are killed P8 . What surm ises would you form as to th e method of

pollination of a flower which h as a large white corolla ,narrowed

below to a tube , with a honey-gland at its base , and whichemits a perfum e towards evening ?

422 INDEX

Arch ich lamydeae,2 32 ,

2 34 ,2 35 ,

Arctium , 263 .

Arenar i a , 38 5 .

Arrowh ead (S agi ttari a) , 37 1 .

Artich oke, Jerusalem (H eli anthus

tuberosus ) , 1 3 1 , 263 .

True (Cynari a S colymus ) , 263 .

Arum,1 34 .

Ash ,Common , 2 3

—4 , 27 ,

2 8,2 1 0 ,

2 1 5 . 2 2 2 . 30 8— 1 1

, 337 . 345 ,

349 , 350 , 353Mountai n ,

1 2 1 , 2 2 5 , 29 8—30 1 ,

348

Ash woods , 349 . 35 0 . 353Asparagus , 1 47 ,

266

Aspen , 279 .

Asph odel , B og , 266 .

Assimilation of carbon d ioxide ,

7 8 ,80 .

Aster , 263 , 382 , 383 .

A triplex, 37 8 , 383 , 387 .

Atropa ,2 5 5 .

Atropine,2 54 .

Attitudes o f plants , 1 47— 8 .

Aubreti a ,2 38 .

Au tumn Crocu s , 1—57 , 266 .

Avens , Mountain ,244

Water, 2 2 5 , (Fig . 2 44 , 349 .

Awn , 2 0 2 , 2 27 , (Fig .

Axillary branch es , 1 2 .

Axis , ascend ing ,1 2 .

d escend ing ,1 2 .

Bacteria , 2 2 0 , 324 .

in root nodu les , 326 .

in soil , 32 5—6 .

n itrO 32 5— 6 .

Balsam , 74 , (Fig . 2 2 8, (F ig .

Bamboo ,2 64 .

Banana , 2 1 1 , 2 1 8 .

h ow propagated , 2 1 8 .

Barberry, 2 2 5 , 339 , (F ig .

Barley, 54 ,26 5 .

B artsi a , 2 56 , 379 .

Bast, 69 , 7 0 .

Beaked P arsley, (see Ch ervil) ,380 , (F i g .

Beam , Whi te , 349 .

Bean,Broad ,

1 9—2 3 , (Figs . 6 ,

2 5 , 2 8 , 37 (Fig . 87 ,1 90 ,

Bedstraw, 348 , 36 1 .

Lady’s, 369 .

Marsh , 37 6 .

Yellow , 37 0 , 380 .

Beech ,1 1 4

— 1 8 , (Figs . 7 2 , 741 48 , 2 0 5 , 2 1 2 ,

2 36 , 2 89—9 1 ,

(F 1 gs . 1 9o—I ) , 34 5 , 352 , 35 3

4 , 360

Beet, 59 , 60 ,1 2 5 .

Belladonna ,2 54 .

B ellflower , 1 5 5 .

Nettle- leaved , 353 .

B elli s , 262 , 380 .

Bent-grass , 367 .

Berry, 2 1 8— 1 9 .

Betony, Wood ,2 54 , 37 0 .

B etula,2 36 .

Betu laceae , 2 36 .

B i dens ,2 63 .

Biennials , 1 24—5 , 379 .

Bi fo liar spu r, 1 1 8 .

B ignoni a ,2 2 2 .

Bilberry, 3 1 7 , 348 , 368 ,

edge , 39 1 .

moor, 3 1 7 , 39 1 , (Fig .

Bindweed , 34 1 , 379 .

Black, 37 8 .

S ea , 385 .

Binom ial system ,2 3 1 .

Birch ,1 2 1

,2 2 2 , 2 36 , 2 83

—6 ,

(F ig 294 , 345 , 348 ,

352

Birch wood , 352 .

Bird ’

s- foot Trefoil , 386 .

Bird ’

s-nest, Yellow, 356 , 357 .

Bird ’

s-nest Orch id , 356 .

Birthwort, 68, (F i g .

Bistort, Water, 37 5 .

Bitter Cress , 348 .

Large , 37 0 , 376 .

Bittersweet (see Woody Nigh tsh ade) , 1 1 6 .

Blackberry (Bramble) , 2 I 7 , (F ig .

2 1 9 .2 24 .

2 2 5 . 242 ,

Blackth orn ,1 1 9 ,

2 2 5 , 339 .

Bladder- fern ,Brittle , 349 .

Bladderwort (Utri culari a) , 365 ,(F la 37 2

Bladder-wrack, 38 1 .

Bleed ing , 98 .

Blinks , Water, 34 3 .

Bloom on leaves and fruits , 9 5—6 .

INDEX 423

Bluebell (Wild H yac inth ) , 34 , 6 0 ,

77 ,1 37

—40 , (R s 1 54 .

(Fi gs . 1 0 1 , 1 94 , (F i g .

2 0 2,2 0 6 ,

266 , 269 , 343 ,

348. 3 5 0 , (F lg . 369Borage ,

2 5 0 .

Boraginaceae , 2 50 .

B orago , 2 50 .

Box leaf,

structure of , 6 5—7 ,

(Figs . 29 ,

Bracken. 68 , 1 4 1 , 340 . 34 3. 348.

349 , 35 0 , 35 9Bramble , 62 , 2 24 , 339 , 387 .

S tone, 349 .

Branch spines , 339 (Fig .

396. (F laBranch es , sh edd i ng of , 1 1 8— 1 9 ,

1 2 2 .

Branchi ng ,1 1 9

—2 1 .

B rassi ca ,2 38 , 37 8 .

Broccoli , 2 38 .

Brome-

grass , False , 349 .

Soft, 379 .

B romus , 379 .

Brookl ime , 2 56 , 343 , 37 6 .

Brookweed , 2 50 .

Broom ,2 27 , 246 , 344 .

Broomrape (Orobanche) , 343, 359 ,360 .

Brussels Sprou t, 1 0 3—4 , (Fig .

2 38 .

Bryony, Black , 1 43 , (Fig .

1 44 ,2 2 5 , 34 1

1 47 ,1 49 .

Buckthorn , 349, 35 3 .

Bu ckwh eat, 56 .

Buds , 1 2,1 0 3

—2 2 .

dormant, 1 2 1 — 2 .

naked ,1 0 4 , 1 1 6 .

protection o f , 1 0 9 .

winter, 224 , 374 .

Bud -scales , 1 0 6 .

scars of , 1 0 8—1 8, (Figs . 66 , 7 0 ,

74 . 7 7 )Bugle, 2 54 .

Bu lbs, 1 34—40 .

descent o f , 1 34 ,1 39 .

Bu lrush ,2 2 2 .

Burdock, 2 26 (Fig . 263 .

Burnet, Great, 349 , 380 .

Lesser or Salad ,244 , 368, 37 0 ,

380 .

Bu r-reed , 37 1 , 37 6 .

Bu tch er’s Broom ,266 , 354 .

Bu tterbur, 262 .

Buttercup , 1 66—8, (Fig .

1 74 , 1 92 ,2 0 4 , 2 0 6, 2 1 2 ,

(I fig. 1 44tCreepi ng , 389 .

Field , 37 8 .

runner of , 67 , (Figs . 3 1 ,Tuberous , 1 66 , (F ig .

Uprigh t, 380 .

Water, 37 1 , (Fig .

Bu tterwort (P ingu i cula) , 362 ,

363 .

Cabbage ,1 0 4 , 2 38 .

Cactus , 1 47—8, (Fig .

Caki le, 387 .

Calcareous grass- land , 368 .

Calli tr i che, 343 .

Calluna , 3 1 7 , 387 .

Callus , 7 2—3 .

Caltha , 343 .

Caly stegi a , 385 .

Calyx , I 5 .

function of , 1 5 .

Cambium , 35—6 , 69 .

ring , 36 , 7 0 .

Campanu la ,1 5 5 , 2 1 6 , 2 2 3, (Fig .

26 1 . 353Campion, 68 , 2 1 6 .

Alpine , 2 39 .

Bladder, 2 39 , 37 8 .

Moss , 2 39 .

Nigh t-flowering , 242 .

Red , 2 0 4 , (Fig . 2 2 3 , 2 39 ,27 0 .

Sea ,2 39 .

Campylotropous , 2 0 8 .

Canadi an Water-weed (E lodea) ,80 , (Fig . 2 2 3, 37 2 .

Capitu lum,1 77 .

Caprifoliaceae , 2 58—60 .

Capsella , 37 8 .

Capsicum , 2 5 5 .

Capsu le, 2 1 6—I 7 , (Figs . 1 5 1 ,Caraway seed s 2 1 5 , 247 .

Carbon -assimilation, 84 5Carbon d ioxide in respiration,

44 .

Carduus , 379 .

Carex, 380 , 385—6 .

Carina ,1 88

, (Fig .

424 INDEX

Carmine ,89 .

Carnations , 9 5 , 2 39 .

Carni vorous plants , 36 1 .

Carpel , 1 7 , 2 0 ,1 58 .

Carpophore,2 1 5 , (Fig .

Carrot, 59 , 1 24 , 246 , 380 .

Carum,247 .

Caryophyllaceae ,2 39

—42 .

Castanea , 30 6 .

Castor-Oi l seed ,2 1 0 , 2 26 , (Fig

1 6 1 )Catchfly (S i lene angli ca) , 68 , 24 1 ,

Catkins , 1 59 ,276

—94 .

Cat’s-ear , 380 , 385 .

Cat’s-tail-grass , 386 .

Caucali s , 247 .

Cau liflower, 238 .

Cayenne pepper, 2 5 5 .

Celand ine ,Lesser, 60 , 62—4 , (F ig .

1 3 1 , 1 42 , 2 0 6, 350 .

Celery, 246—7 .

Cell-wall , 48 .

Cellu lose , 4 8 .

Censer fruits , 2 22—3 , (Fig .

Centaurea ,262 , 380 .

Cephalotus , 36 5 .

Cerastiurn, 3Chaerophyllurn Anthri scus)

Charlock, 1 24 , 37 8 .

Wh ite , 37 8 .

Chemical elements necessary forp lants , 5 5—7 .

Chenopodiurn, 37 8 , 387 .

Ch erry , 1 7 0 (F ig . 1 7 1 , 2 1 7 ,

(Fig . 2 24—5 .

Bird , 348 .

Winter, 2 1 0 , 2 54 .

Ch ervi l , or Beaked P arsley, 1 7 34 . (Fig I I 9) 1 93. 2 0 4 ,

2 1 5 .247 , 343

Ch estnu t, Sweet or Edible, 2 1 2 ,

Chi ck-

pea ,1 47 .

Ch ickweeds , 1 24 ,2 39 , 242 ,

37 8

Mouse- ear, 369 , 380 .

Water, 2 39 .

Chlorophyll , 67 , 84—5 .

cond itions necessary for

formation , 77—8 .

and starch , 80 —6 .

Ch loroplasts (ch lorophyll cor

pu scles) , 67 , (Fig . 85 .

Ch ristmas Rose , 2 37 .

Chry santhemum,262

, 378 , 380 .

Cicely , Sweet, 247 .

Cinc innu s , 24 1 .

Cinqu efoil , Creeping , 379 .

Circ innate , 1 1 9 .

Class , 23 1 .

Classification o f P lants , 2 29—34 .

hi story o f , 2 29—3 1 .

Claw ,I 6 .

Cleavers , 2 2 5 , (F ig . 37 8 .

Cleistogamous flowers, 1 86 , 2 0 3 .

Clematis , 90 ,1 44 , (Fig . 1 64 ,

(F ig . 1 68 , 2 2 2 , 2 37 ,

34 1 .

Climbing organs , 1 43—7 , 340

—1 .

plants , 1 43—7 . (FigS 89

340—1 .

Clover, Whi te ,1 49

—50 , (F ig .

63 9Club- rush , Marsh , 37 6 .

Cochleari a , 383 .

Cock’s-foot-grass , 368, 37 0 .

Cohort, 2 3 1 .

Colchi cum,1 57 ,

266 , 353 .

Cold , e ffect of , 3 1 5 , 335- 6 , 394—5 ,

397Collenchyma , 68 .

Colonization , 2 2 0 .

Coltsfoot, 1 5 5 , 1 79- 80, (Fig .

2 1 4 , 2 22 , 2 62 , 379 .

Columbine , 1 5 5 , 1 86—7 , (Fig .

1 92 , 2 37 .

Comfrey, 2 5 0 .

Compani on cells , 69 .

Comp lementary societies, 350

- 2 ,

(Figs . 2 2 5 ,Compositae ,

2 0 4 , 2 2 1 , 260 —3 .

Conifers, 27 0—6 , (Figs . 1 80 ,1 82—4)

Con ium, 246 .

Connate , 260 .

Conopodi um,247 , 380 .

Convallari a , 266 .

Convolute , 1 1 9 .

Convolvulus , 379 .

Coppice , Ash , 30 8 .

H azel , 2 8 1 .

Willow , 27 7 .

Coral-root, 269 , 35 3, 356 , (F ig .

2 2 8}

426 INDEX

Deadnettle , R ed ,2 54 , 379 .

Whi te ,2 54 .

Yellow, 348 .

Delphinium, 237 .

Deschampsi a , 367 .

D iadelphou s, 1 88 .

D i anthus , 2 39 .

D iastase, 86 .

Diatoms , 2 2 0 .

D ich asium ,2 39 .

D ich ogamou s , 2 0 4 .

D ich otomy, false , 2 39 .

Diclinous , 2 0 4 .

D icotyledons , 24 ,1 94 ,

2 30 2 32 ,

- 63D i ervi lla ,

2 58 .

Digestion of nitrogenou s food ,

362—6 .

o f starch ,85—6 .

D igi tali s , 2 56 .

D imorphi c flowers , 1 7 7 , (F ig .

2 0 4—5 .

D isk florets , 1 7 8 .

D itch es , p lants o f , 343 .

D ioec ious, 1 60 , 2 0 4 .

D i onaea , 366 .

D ivi-d ivi (Caesalpin i a) , 245 .

Dock, 6 1 , 1 1 9 , 2 0 5 , 379 .

Curled , 389 .

Dodder, 343, 360 — 1 , (Figs . 230— 1

Dog Daisy, 2 62 .

Dog’

s Mercury, 1 27 , 20 4 , 343,

Dogwood . 2 2 5 . 349 , 35 3 .

Dormant buds , 1 2 1 —2 .

Dracaena , 264 , 266 .

Drip-tip , 34 1 .

Droppers , 1 37 , (Fig .

Dropwort, Water, 247 , 343,

37 0

Drupe , 2 1 7 .

Drupels , 2 1 7 .

Dryas , 244 .

Du ckweed , 59 , (Fig . 60 ,

37 2

Dunes, 383—7 .

fixed, 386 , 387 .

grey , 386 .

shi fting , 386 .

travelling , 386 .

whi te , 386 .

Dwarf sh oots , 1 1 7 ,1 1 8

, (Figs .

7 4. 27 1—3 , (P le

Earth -nut , 247 , 380 .

E ccremocarpus , 2 2 2 .

E chium, 2 50 , 379 , 389 .

E cology, 3 1 5—2 0 .

Edelweiss , 263 .

Egg-cell , 2 0 7 ,

2 0 9 , 2 1 0 .

Egg-nu cleus , 2 0 9 .

E lder, 1 4 , 7 1 , (F ig . 1 1 9 , 2 2 5 ,2 58 , 387 , 389 .

Elm,1 1 6 ,

1 1 7 , 1 2 0 , (F i g .

1 2 2 ,1 48 , 2 1 5 , 2 2 2

, (F ig .

29 5 1 97337 , 360 .

Elodea ,8 0

, (F i g .

Embryo , 2 1,2 3, 24 , 30

—4 , 2 0 9

1 0 .

Embryo -sac ,2 0 7 , (F ig .

2 0 9—1 0 .

Ench an ter’s Nigh tshade (Ci r o

caea) , 354 .

Endocarp , 2 1 7 .

Endod ermi s , 35 , 7 0 , (Fig .

Endosperm , 32 , 34 , 2 0 9— 1 0 .

Entomophi lous flowers , 2 0 5 .

Envi ronment , 64 .

Eosin ,89 .

Eph emerals , 1 24 .

Epicalyx ,1 68, (Fig .

Epicarp , 2 1 7 .

Epidermi s , 34 .

Epigeal , 2 5—9 .

Epigynous , 1 7 1 .

Epi lobi um, 343. 379Epipacti s , 269 .

Eranthi s , 2 38 .

E ri ca . 368 , 387 . 394Erodi um, 386 .

E ryngi um, 247 , 385 .

E ssential organs of reproduction ,

1 60 .

E tiolation , 7 7—8 .

Euonymus , 353 .

Euphorbi a , 379 , 385 .

Euphrasi a , 2 56 , 379 .

Evening P rimrose, I 53—4 , (Fig .

I ooyExstipu late, 1 1 6 .

Extrorse deh iscence, 1 96 .

Exudation pressure , 98, (Fig . 60 )Eyebrigh t. 2 56. 359 , 369 , 379 .

380 .

R ed , 379 .

‘

Eyes 1 2 8—9 .

INDEX

Factors, 3 1 7 , 335 .

c limatic , 3 1 7 .

edaphi c , 3 1 7 .

topographi c , 3 1 7 .

Fagaceae , 2 36 .

F agus , 2 36 ,2 89 .

False fruits , 2 1 9 .

Fami ly, 2 3 1 .

Feath er-grass (S tipa ) , 2 2 2 .

Feh ling’

s solu tion test for grapesugar, 86 , 1 3 1 .

Fennel,247 .

Ferns , 2 20 , 2 2 1 , 2 3 1 .

Bladder, 349 .

Lady, 348 .

Male , 348 , 369 .

Marsh , 35 3 .

Fescue—grass , 385 , 386 .

Meadow, 37 0 .

Sh eep ’

s , 367 , 368 , 37 0 .

F estuca , 367 , 385 , 386 .

Fibrous roots, 59 .

Fig ,2 1 0 ,

2 1 9 .

Figwort, 2 56 .

Filament, 1 5 , I 6 , 1 58 .

Fir, S cotch (see P ine ) , 270 .

Douglas , 353Fixed - ligh t posi ti on ,

1 47—8 .

Flag ,Yellow,

267 .

Flax , 36 1 .

New Z ealand , 266 .

Purgi ng , 369 , 379 .

Floral d i agram ,1 7 .

Flowering Rush ,1 2 8 , (F ig .

Flowers , 1 4— 1 8 .

biology of , 1 56—2 0 3 .

explosive ,1 9 1 .

irregu lar, 1 7 3pollinati on of , 1 56—2 0 3 .

structure o f , 1 4— 1 8 .

F oeni cu lum, 247 .

Follic le ,2 1 6 , (Figs . 1 49 ,

Forget-me-not , 2 50—2

, (Fig .

263 .

Corn , 37 8 .

Water, 376 .

Foxglove ,1 2 5 , 2 56 , (Fig .

343F ragari a,

243 .

F raxinus , 30 8 .

F reesi a , 267 .

Fri tillary, 266 .

427

Frog-bit , 60 , 37 2 .

Fruits , 1 7—1 8, 2 1 1 —1 9 , (Figs 1 4 3

5 5 )d ispersal of , 2 1 9—2 8 , (Figs . 1 56

6 22 )dry , 2 1 1

— 1 7 .

explosive , 2 1 5 1 7 , 2 261 62 )

stru ctu re of , 2 1 1 — 1 9 .

su ccu lent, 2 1 7— 1 9, (Figs . 1 522 24

—5 ‘

F uchs i a , 97- 8 .

F ucus , 38 1 .

F umari a, 37 8 .

Fum itory, 37 8 .

Climbing , 34 I .

Funicle ,1 9—24 , 2 0 7

—8, (Figs . 6—9 ,

Fungi , 2 2 0 ,2 24 ,

2 3 1 .

work Of : 32 5 : 354 : 357 °

F unki a , 266 .

Furze (see Gorse) .

Galanthus , 267 .

Galeopsi s , 2 54 , 379 .

Gali um, 37 8 , 380 .

Gamopetalous , I 7 5 .

Gamosepalous , 1 7 2 ,1 74 .

Garlic , 1 4 1 , 266 , 343 , 348 .

G ean , 354 .

Geni sta , 246 .

Genus , 1 1 , 2 3 1 .

Geotropism , 38-

9 .

negative , 39 .

posit ive , 39 .

Geophytes , 1 40 .

Gerani um, 37 8 , 389Gerani um (P elargon i um) , Garden,

74 .8 1 —3 1 7 2 (Figs 52 ,

‘ 1 1 -7Field

,1 7 2 , 1 74 , (Fig .

Germination , 24—34 .

Geum, 244 .

G ipsy-wort, 2 5G laddon (see Yellow Flag) , 268 ,

35 3Gladi olus , 1 34 , 267 .

G lasswort , 382 , 383 .

Glauci um, 389 .

Glaux, 249 , 383 .

Glori osa,266 .

G lumes , 2 0 1 , (F i g .

Glyceri a , 343 , 37 1 , 383

428 INDEX

Gnaphali um, 263 , 37 8 .

Goat’s-beard (Tragopogon) , 343 ,379

Gooseberry, 1 47 . (Fig . 2 1 8,

(I fig . 1 54%Goosefoot , 37 8 , 387 .

Gorse , 1 90— 1

, (Figs . 1 32 ,

— 6

Gourd , 2 1 8 .

Gramineae , 26 5 .

Grape , 86 , 2 1 1 , 2 1 8 .

Grasses , 1 42 , 2 0 0 — 2 ,2 0 5 , 2 26 ,

2 27 , 264—5 , 269 , 343

Grass- land , 366—7 0 .

c alcareous , 368 .

neutral , 368 .

Grass-moors , 367—9 , (Fig . 2 3Grass-wrack, 37 5 , 383 .

Gravity, 2 8 , 38 .

Groundnu t , 246 .

G roundsel , 1 4 ,1 24 , 2 2 2

,262 ,

Growth ,cond i ti ons necessary for ,

34o i root , 2 2—5 .

o f shoot , 2 5—9 , 32—3 .

rate of , 77 .

Guelder-Rose , 2 2 5 , 2 58 , (Figs .

Gymnosperms , 2 32 , 2 33 , 27 6 .

Gynobasi c , 2 5 0 .

Gynoecium ,1 6 ,

1 58 .

H abenari a ,269 .

H ai r-grass , tu fted , 376 .

VVaved . 344 . 348 . 367 . 368 ,

369 . (FfigHalophytes , 3 1 8 , 382 , 389 , (Fi gs .

2 1 1,

Hangers 353 .

Hassocks , 39 1 .

Haustorium , 360 , (Fig .

Hawk-bit,Au tumnal , 380 .

H awk-moth flowers , 260 .

Hawkweeds , 262 , 369 , 385 .

H awth orn , 62 ,1 1 6 ,

1 2 1,

2 2 5 ,244 . 337 . 339 . (Fig348 .

Hazel , I 4 , 62 ,1 1 6 ,

1 1 7 ,1 59 ,

1 92 ,2 0 4 , 2 0 5 , 2 1 1 — 1 2 , 2 36 ,

2 8 1 —3 , (F 1g 1 87» 294 . 349 .

35 3: 354H eart-wood , 7 1 .

H eath vegetation, 3 1 5 (Figs .

2 5 1 387 .

H eath s , 54 . 2 2 1 , 235 . 263, 344 ,

387 . 392 . (F 1g - 2 5 3LCross- leaved , 1 7 5 , (F i g .

.

1 93, 368 , 394 , (F i g.

Fi ne-leaved , 394 , (F i g . 2 53)H eath er-moor

, 393—5 .

Hedgerows , 2 24—5 , 336—44 , (Figs .

2 1 8

H eli anthemum, 368 .

H eli anthus,262 .

H eliotropism , 4 2 , 7 6—7 , (F ig . 46)

negative , 4 3 .

H ellebore , 349 .

H elleborine , 269 , 349 , 353—4 .

H elleborus , 2 36 .

H emlock, 246 .

H emp Nettle ,1 24 , 379 .

H enbane,2 1 7 , 2 5 5 .

H eracleum,247 , (Fig .

H erbaceou s , 1 2 .

H erb Robert , 343 , 37 8 , 389 .

H ermaph rod ite ,2 0 4 ,

295 .

H eteromorph ic , 2 0 4—5 .

H eterophylly, 37 2 , (Fig .

H ibernating organs, 1 2 5—42 .

H i eraci um, 385 .

H ilum , 2 1 .

H ip . 2 1 2— 1 4 , (F ig .

H ippocrepi s , 368 .

H ippophae, 385—6 .

H ogweed ,2 1 5 , (F ig . 2 2 2 ,

(F ig 1 56»H olcus , 368 , 380 .

sea ;247 ) 385 ‘

H onesty (Lunari a) , 2 1 6 , 238 .

H oney-dew , 30 4 .

H oney-gu ides , 1 85 .

H ooked fru its , 2 2 5- 6 , (Fig .

2 52 .

H op , 36 1 .

Hornbeam ,1 1 7 , 2 2 2 , (Fig .

2 36 .

Horse-Ch estnu t , 1 0 8— I 3, (Figs .

68 ,1 1 4 ,

1 1 6 , 1 48, 1 54 ,

(F i g . 30 6— 8

, (F i g .

Horsetail Smooth (or Water)

Marsh . 37 5 , 376H ottoni a ,

249 .

430 INDEX

Leu coplasts , 87 .

L ifting power of shoot, 76 , (F ig .

4 5 )Ligature of stem , 90 , (Fig .

Ligh t , effect of , 7 6—7 .

absorbed by ch lorophyll , 88 .

Ligu late florets , 1 7 8, (Figs . 1 2 2

4Ligu le , 3 1 , 32 .

Ligu liflorae ,262 .

L ilac , 263, 3 1 1 — 1 4 , (F ig .

L iliaceae , 26 5— 6 , (Fig .

Lily (Li lium) , 1 34 ,2 66 ,

269 .

L ily-of—th e-valley, 1 27 , (Fig .

Limb , 1 5 , 1 6 .

Lime-tree ,1 2 2

,1 48 .

Limonium, 383 .

L inari a ,2 56 .

Ling , 348 , 36 1 , 368 , 387 .

L innaea , 260 .

L inum, 379 .

Li stera , 269 .

Lod icu les , 2 0 2 , (F ig .

Lolium, 368 .

London P ride ,1 0 5 .

Loni cera ,2 58 , 2 60 , 387 .

Loosestrife ,1 77 ,

2 50 .

Purple , 2 0 5 , 37 0 .

Lotus , 386 .

Lousewort , 2 56 , 359 , 37 0 .

Love-in-a-mist (Ni gella ) , 2 38 .

Lungwort , 2 50 .

Lupin (Lupinus) , 246 .

Luzu la , 380 .

Lychni s , 2 39 , 24 1 , 37 8 .

Lycium,2 5 5 .

Lycopus , 2 54 .

Ly simachi a ,2 50 .

Madder, Field , 37 8 .

Maize , 30 , 33—4 , 54 , 1 26 , 2 1 0 ,

2 1 4 , (Figs . 1 2 and

Mallow ,2 0 3 , 2 0 6 .

Round - leaved ,1 60 , (Fig .

Mandrake (M andragora ) , 2 5 5 .

Maple ,2 1 5 , 2 2 2 , 35 3 .

Maps of a wood , 347 , (F ig .

Marigold ,Burr, 2 2 5—6 ,

26 3 .

Corn , 37 8 .

Mars} ,1 64

—6 , (F ig . 1 92 ,

2 0 6 ,2 1 5

— 1 6 , (F ig . 343 ,

Mare’

s-tail (H ippuri s) , 37 IMarjoram ,

2 52 .

Marram -

grass , 1 27 , (F i g .

1 4 1 . 384 , (FigS 247Marsh plants , 343 , 37 5— 6 .

Mat -grass , 367 , (F ig . 368 .

M atri car i a , 37 8 .

M a tthi ola ,1 1 .

Mayweed, 37 8 .

Mead -

grass , 37 1 .

Floating , 343 , 37 1 .

Meadow Ru e,2 37 , 368 .

Saffron (see Au tumn Crocus) ,I S7 , 3S3

Meadow -sweet, 243 , 353 .

Meadows , 368—9 .

Meal—tree , 1 1 6 .

Mech anical supporting tissue , 68

(F lgs . 34 . 36. 38—40 )

M edi cago ,2 2 2

, 37 8 .

Med ick, 246 , 37 8 .

Megasporang ium ,1 59 .

Megaspore ,1 59 .

Megasporophyll , 1 591M elampyrum, 2 56 , 353 .

M entha ,2 5 2 ,

2 54 , 379 .

Mericarp,2 1 5 , (F ig . 246 .

Mesocarp , 2 1 7 , (F ig .

Mesophytes , 3 1 8 .

Metach lamydeae , 2 32 ,2 35 , 248

3Micropyle , 2 1 , 2 5 , 2 0 7 .

M icrosporangia ,1 5 8 .

Microspore , I 5 8 .

Microsporophyll , 1 58 .

M idrib , 1 2 .

Mi lkwort , Sea , 249 .

M ilfoil , Water (M yri ophyllum) ,37 2 1 37 5 2

M imosa ,1 5 2 , 24 5 .

M imulus , 2 56 .

Mint, Com ,2 54 .

Field , 379 .

Garden ,2 52 .

Water, 2 54 .

Mistletoe, 1 I 6 , 35 8 .

M olini a , 368 .

Monadelph ous , 1 6 1

Monkey-flower , 2 56 .

Monksh ood ,1 87

—8, (Fig . 1

Monocotyledons , 30 , 32—4 , 7 0

1 94— 2 0 3, 2 32 ,

264—9 .

INDEX 43 1

Monoeciou s , 1 60 , 2 0 4 .

Monopod ial branchi ng ,I 1 9—20 .

M onotropa , 356—7 .

Moor-grass , Purple , 368 .

Moorland plants , 390 —7 .

Mosch atel , 343 .

Mosses , 2 2 0 ,2 2 1 , 2 3 1 .

Motile organs , 1 49 .

Mountain Ash ,1 2 1 .

Movements of flowers and fruits ,1 5 2

—5 .

of plants , 1 42 .

protective , 1 48 ,1 52 .

Mu lberry, 2 1 0 ,2 1 9 .

Musk, 2 56 .

Mustard ,2 5 , 27 , (F ig . 2 8

,

2 38 .

H edge , 37 8 .

Mycelium , 354—5 .

Mycorrhi za , 35 5—7 , (F ig . 2 29A) .

M yosoti s , 2 5 0 , 37 8 .

M yrrhi s , 247 .

Myrsiphy llum,1 47 .

Narci ssus , 267 .

Nardus , 367 .

Narthecium, 266 .

Nasturtium , Garden, 97 , I 7 3,(Fig .

Nectaries , 1 60 , 1 98, 2 0 6 .

extra floral , 2 0 6, 2 58, 340 ,

(F i g . 365 .

on ovari es , 1 64 ,1 74 ,

1 7 5 , 1 77 ,1 79 ,

1 8 1 , 1 9 5 , 1 97 ,2 0 6 .

on petals , 1 66 , (Fig . 1 86 ,

(F ig . 1 88,1 98 , 2 0 6 .

on receptacle , 1 69 ,1 7 0 ,

1 7 1 ,1 7 2 , (Figs . 1 1 7 , 1 7 3,

on sepals , 2 0 6 .

on stamens , 1 6 ,1 7 2 ,

1 85 , (Fig .

2 0 6 .

Neotti a , 356 .

Nepenthes , 365 .

Nepeta ,2 54 .

Nettle, H emp , 2 54 , 379 .

S tinging , 68. 343. 353. 36 1 . 379 .

Neu tral grass- land , 368 .

Ni coti ana , 2 54 .

Nicotine, 2 54 .

Ni gella , 2 38 .

Nigh tsh ade , Dead ly, 2 5 5 , 354 .

Enchanter’s , 2 2 5 , 354 .

Nigh tsh ade , Woody, 1 1 6 , 1 82—3 ,(Fig ' 2 2 5 : 2 54 : 263:

Ni pplewort, 379 .

Nitrates , 32 5 .

Nitrification , 32 5—6 .

Nitrites , 32 5 .

Nitro -bacteria , 32 5—6 .

Nu cellu s , 2 0 7 , (Figs . 1 40

Nuc leu s , 48 , (F ig . 2 0 9 , (F ig .

Nutation ,1 4 3 .

Nu tlets , 2 1 2 , (Figs . 1 44Nu trition, 5 5—8 .

in insec tivorou s plants , 36 1 —6 .

in leguminou s plants, 24 5 ,

326 .

in parasites , 358—6 1 .

in saprophytes , 3 5 5—7 .

Nu ts , 2 1 1 , 2 1 2 , (F ig . 2 26 ,2 83 , (Fig . 29 1 .

Oak ,1 4 ,

1 1 6 ,1 2 2 ,

1 59 ,1 92 , 20 4 ,

2 0 5 , 2 36 , 29 1 , 294 , (Figs .

1 92—4L

P eduncu late , 29 1—2

,294 .

S essile , 29 1—2

,294 .

Oak woods, 347—5 2 .

d ry , 347 .

moist, 348. 349 .

Oat , 34 , 2 1 4 , 265 .

Obd iplostemonous , 24 1 .

Oenanthe. 247 , 343 .

Oi l stored in seed s , 2 3 .

Oi l-bod ies on seed s , 2 26 , (F ig.

On ion , 34 , 86 , 266 .

Onon i s , 246 , 379 , 380 , 386 .

Ophrys , 269 .

Orach e , 37 8 , 387 .

Orange , 2 1 1 , 2 1 8 .

Orchi daceae , 268—9 .

Orchi ds , 1 98 , 2 0 3 , 2 2 1 , 268—9 .

Orchi s , B ee , 269 .

Bird ’

s-nest, 356—7 .

Butterfly, 269 .

Early P u rple ,1 98

—2 0 0 , (Fig .

269 . 343. 349F ly ,

269 .

Spider, 269 .

Spotted ,269 .

Order, 2 3 1 .

Origanum,2 52 .

432 INDEX

Orni thogalum, 266 .

Orthotropou s , 2 0 8 .

Osier Willow, 2 35 , 27 6—7 .

Osmic acid ,2 3 .

Osmometer, P otato , 52—3 , (Fig .

Osmosis , 50 —4 .

Ovary, 1 7 ,1 59 .

Ovu le ,1 7 ,

1 59 ,2 0 6—8 .

Oxali s , 1 50— 1

, (Fig . 2 0 5 .

Oxygen ,necessity for , 4 3

—5 , 57 .

P ales , 20 1 , (Fig .

P alisade tissu e , 66 , (F ig .

P alms , 264 .

P ansy, 1 8 5—6 , (Figs . 1 27

Corn ,1 86 , 2 0 4 ,

2 0 6 , 37 8 .

Field , 1 24 .

P apaver , 37 8 .

P apilionaceae ,244

—6 , (F ig .

248 .

P appus , 1 80 .

P arachu te fruits , 2 2 1 —2 .

P arasites , 34 3 , 35 8—6 1 , (FigS

2 29P aris , H erb, 2 66 , 353 .

P arsley , 247 .

Beaked (see Ch ervil) , 1 7 3 , 380 .

Fool’s , 247 , 37 8 .

H edge ,247 .

P iert , 37 8 .

P arsn ip , 246 .

P assion -flow er , 1 44 ,1 47 , (F ig .

93P astu res , 366—9 .

survey of , 369 .

P ea ,Ed ible or Garden, 2 1

, 2 3 ,27 ,

2 8 ,87 ,

1 1 6 ,1 90 , 2 1 0

,

Meadow , 380 .

P eanu t , 246 .

P ear, 1 1 9 ,1 7 1 , 2 1 0 , 2 1 9 ,

244 .

P earlwort , 2 39 .

P eat. 3 1 5—1 7 , (Fig 39 1—5 .

P ed icel , I 5 .

P edi culari s , 2 56 .

P elargonium, 74 ,8 1 , 82 ,

1 7 2 .

P elveti a , 38 1 .

P ennywort (Cotyledon) , 344 , (Fig

Marsh ,247 .

P entamerous , 24 1 .

P entstemon ,2 56 .

P epper, 2 1 0 .

P eppermint , 2 52 .

P erennation ,1 2 5 .

P erennials , 1 2 5 , 379 , 380 .

P erfoliate , 260 .

P erianth,1 94 .

P ericarp ,1 8

, 3 1 .

P erigynou s , 1 69 ,1 7 0 .

P erisperm , 2 1 0 .

P ersicaria , 37 8 .

P etaloid , 1 64 .

P etals , 1 6 .

P etasi tes , 262 .

P etioles , 1 2 .

mech anical structure o f , 68 .

mod ified ,1 47 , (Figs . 9 2

1 5 2 .

P etuni a ,2 54 .

P eucedanum, 246 .

P haseolus , 246 .

P hleum, 386 .

P h loem , 69 .

P hormium, 266 .

P h otosynth esis , 79—80 .

P hragmi tes , 37 1 .

P hylloclade (or c ladode) , 1 47 ,

(Fig . 266 , 37 2 .

P hyllode ,1 47 , (F ig . 366 .

P hyllotaxy, 1 4 .

P hysali s , 2 1 0 ,2 54 .

P impernel , B og , 2 50 .

S carlet , 2 0 4 ,2 1 6 , (Fig .

2 50 .

P impinella ,247 .

P ine-apple ,2 1 0 , 2 1 9 .

P ine , Scots , (F ig . I 1 8—1 9 , 2 0 4 ,

20 5 , 2 2 2 , (Fig . 2 3 1 ,

2 33, 27 0—4 . (Figs . 1 82

P inks , 9 5 , 2 39 , 24 1 .

P inus , 27 0 .

P istil , 1 6 ,1 7 , 3 1 , 1 58

—9 , 20 6—7 ,

(F lg . I 39 )P i sum

,246 .

P itch er-p lants , 365—6 .

P ith, starch stored in , 9 1 .

u se o f , 97 .

P lacenta ,1 7 ,

1 9 , 2 0 , 20 6 .

P lane -tree , 30 4 .

P lant-associations , 2 33—4 , 3 1 9

2 0 : 34 5—99 '

c losed , 387 , 399 .

Open , 387 , 399

434 INDEX

Quercus , 2 36 , 29 1—4 , (Figs . 1 9 2

4

Qu icken- tree ,298 .

Qu ick-grass , 1 2 5 , 1 40 .

Qu ince , 244 .

Raceme , 1 5 , 1 94 , (F ig .

Rad icle, 2 0 ,2 1

, 2 2 ,2 3 .

pocket, 2 0 — 1 .

Radi cula, 343 .

Rad ish , 35 , 59 , (F ig . 1 2 5 ,2 38 .

Horse ,2 38 .

Ragged Robin, 2 39 , 37 0 , 37 6 .

Ragwort, 262—3 , 37 0 , 380 .

Ranuncu laceae , 2 36 , 24 2 , 248 .

Ranunculus , 2 36—7 , 343, 37 8 , 380 .

Raphanus , 37 8 .

Raspberry, 62 , (F ig . 1 2 2 ,

2 1 7 ,2 2 5 , 24 2

—3 .

Ray-florets , 1 7 8

- 80 .

Receptac le ,1 5 , 1 6 .

-cup ,1 7 0 ,

1 7 1 .

Reed ,Common , 37 1 , (F ig .

637Region of elongationin roots , 4 5 , 46 , (F ig .

in shoots, 47 (Fig .

Replum ,1 7 .

Reproduction, vegetative ,1 40

—2 .

in aquatic plants , 374 .

Reprodu ctive organs , 1 4— 1 8

,

2 0 6— 1 1 .

Respiration, 43, 44 ,1 0 7 .

Rest-barrow, 246 , 379 , 380 , 386 .

Revolute ,I 1 9 .

Rhinanthus , 2 56 , 379 .

Rhi zomes, 1 2 5—8

, (Figs . 79—8 1

and 1 I o ) .Rhododendron, 89 , 9 3 , 1 1 9 .

R ibwort (see P lantain) , Io5 , 1 0 6 .

R ice , 26 5 .

Roan-tree, 298 .

Rock-plants , 383 .

Rock Rose, 368 .

Root , 1 2 .

abnormal, 59

—60 , (F ig .

absorption by , 48 , 57 .

aerial , 60 .

aquatic , 60 .

bast (ph loem ) of , 35 .

-branch es, 1 2 .

cambium of , 35 .

Root-cap ,1 2 , 5 8 .

contac t stimu lus , 40 .

contractile , 1 34 , (F ig .

1 39 . (F i g . 87 )cortex of , 34 .

curvature o f , 46 , 47 .

d icotyledonou s , 34—6 .

d irection o f growth , 37 , 38 .

effect of dry and moist so ilson , 42 .

effect o f ligh t on , 42—3 .

endodermis o f , 35 .

environment of , 64 .

epidermis o f , 34 .

excretion by , 49 .

forms Of , 58—64 .

geotropism , 38—40 .

growing region o f , 4 5—6 .

-h air region, 4 8 .

-hairs , 1 2 ,27 , 48 , 6 2 .

hydrotropism , 4 1—2 .

monocotyledonous , 32 , 36—7 .

modules , 245 , 326 , 3 56 .

old , 34 .

oxygen necessary for , 43, 44 .

pericyc le o f , 35 .

-pressure , 97—8

, (F ig .

secondary growth , 35 , 36 .

sensitiveness o f , 38—47 .

sensory region o f , 40 , 4 1 .

separation layer, 1 39 .

stele or central cylinder, 35 .

storage o f food by , 59 , 60 .

structure o f, 34

—7 .

-system,1 2 .

tap , 1 2 , 58 , 59 .

tissues , 34—7 .

tuberous , 60 , 6 2 , (F ig .

vascu lar system of , 35 .

wood (xylem) of , 35 .

work of , 37—58 .

young , 35 » 36 »

Rosa ,244 , 387 .

Rosaceae ,242

—4 .

Rose , 62 , 9 0 ,1 2 2 ,

1 7 0 , (Fig .

1 7 1 , 1 74 , 1 93 , 2 1 0 ,

2 1 2— 1 4 , (Fig . 2 1 9 , 2 2 5 ,244 .

Burnet , 387 .

Rosemary, 2 52 .

R osette plants , 1 0 5 , 1 0 6 , (F i g .

59 ) 2 50 . 344 . 398 . (F 1g . 2 57 )Rosmari nus, 2 52 .

INDEX 435

Rostellum,1 99 , 2 0 0 .

Rowan (see Mountain Ash ) ,244 . 298

—30 1 . (Figs . 1 99 .

Rubus , 243 , 387 .

Rumex, 379 , 380 .

Ruscus , 266 .

Ru sh ,Soft , 376 .

Field, 369 , 380 .

Rush es , 2 26 , 34 8 , 37 0 , 37 5 .

Rye ,26 5 .

Rye-

grass , 368 .

Saccate ,1 6 .

S affron, Meadow (see AutumnCrocus ) , 353 .

Sage ,Gard en ,

2 52 .

Wood ,2 54 .

S agina ,2 39 .

Sainfoin (Onobry chi s ) , 246 .

S t . John’

s -wort, Marsh , 376 .

Salicaceae , 2 35—6 .

S ali corni a , 382—3 .

S alix,2 35 , 386 .

Sallow (see Willow) , 2 35 .

S alsola , 387 , 389 .

Sa lt in soil , 382 , 385 .

S alt-marsh , 3 1 9 , 382—3, (Figs .

2 1 1,

formation, 3 1 9 , 383 .

p lants , 382—3 .

Saltwort, 387—9 .

Samara , 2 1 5 .

S ambucus , 2 58, 387 , 389 .

S amolus , 249 .

Samph ire , 247 , 383 .

Sand -dune (see Dune) , 3 1 8 , 3 1 9 ,

(Figs . 2 1 0 , 246 383—7 .

Sand - sedge , 1 27 , (F ig . 385 ,863

Sandwort, 2 39 , 387 .

S anic le ,Wood , 2 2 5 , 248 , 348,

354 .

S ani cula , 248 .

S ap , 48 ,89 , 90 , 98 .

ascent of , 89 , 90 , 98 .

descent of , 9 0 .

Saprophytes , 35 5—7 , (F ig .

S ap-wood , 7 1 .

S arraceni a , 36 5 .

S axifrage (S axifraga ) , 9 8 , (F ig1 0 5 . 344 .

S cabi osa , 36 8 , 380 .

Scabious , 26 1 , 36 8 .

Field , 380 .

Small , 349 , 368 , 37 0 .

S carlet-Runner, 2 5 , (Fig .

S cent o f flowers , 1 8 .

S ci lla , 266 .

S clerenchyma , 68 , (Fig .

S corpioid cyme , 2 50 .

Scorpion -

grass , 37 8 .

S cots’ P ine (see P ine) , 1 1 8— 1 9 .

S crophular i a , 2 56 .

S cr0 phu lari aceae ,2 5 5 .

S cutellari a , 2 54 .

S cu tellum , 3 1—3 , (Figs . 1 3

S ea Arrow-

grass , 3 83.

Aster, 382 , 383 .

Bindweed , 385 .

E lite , 383 , 388 , 389 .

Buckthorn, 385 , 386 .

Campion , 2 39 , 383, 388 , 389 .

Cat’s- tail , 386 .

Cou ch -

grass , 383 , 385 , 386 .

H olly, 385 .

Kale , 387 .

Knotgrass , 387 .

Lavender, 383 .

Lyme-

grass , 384 .

M ilkwort, 383 .

Orach e , 383 .

P ea , 389 .

P earlwort , 2 39 .

P ink, 383 .

P lantain, 383 .

P oa , 383 .

Purslane ,2 39 , 383 , 38 5 , 387 ,

Rocket , 387 .

Rush , 383 .

Spurge, 385 .

Spurry, 2 39 , 383 .

Sea ’ coast, vegetati on of , 380 —9 0 .

Seaweeds , 38 1 —2 .

S econdary growth , 3 5 , 36 , (Figs1 5 ,

Sedge , 1 42 , 2 0 5 2 26 .

Sand ,1 27 , (F i g . 385 , 386 .

Spring , 380 .

S edum, 389 .

S eed d ispersal, 2 2 I 2 2 2—4 ,2 26—8 .

Seeds of Dicotyledons , 1 9 , 30 .

Of Monocotyledons, 30 —4 .

S elaginella , 2 2 2 .

436 INDEX

S elf-h eal , 2 54 , 380 .

Semi -parasites, 2 56 , 358—9 .

S eneci o, 262 , 37 8 , 380 , 385 .

S ensitive-plant, I 52 ,24 5 .

S epals , 1 5 .

S eparation-layer, 7 2—3 , (Figs . 4 1 ,

4 2 )in leaves , 7 3 ,

3 I O

in roots , 1 39 , (Fig .

in Shoots , 1 2 2 .

Sesleria ,Blue , 37 0 .

Shade ,

8

ef

fec

to f , on growth ,

34S hade plants , 348 .

Shad e position, 1 47 - 8, (Fig .

Sh eph erd ’

s P urse ,1 24 , 2 1 5 , (Fig .

1 5 0 )S herardi a , 37 8 .

Sh ingle beaches , 387—9 0 , (Fig .

249)S h ingle-bind ing plants , 388—9 .

Shootsadventitious, 6o -2

, (F ig .

1 2 2 .

ascent and descent in the so il,1 2 8 , (Fig . 1 34 , 1 37 ,1 39 .

dec iduous , 1 2 2 .

dwarf, 1 1 7 ,1 1 8 , 1 2 1 , (Fig .

effect o f stimu li on , 74—7 .

elongated ,1 2 1 .

environment o f , 64 , 6 5 , 1 2 3—4

growing region, 47 , (F ig .

growth of , 2 5 30 .

mod ified , 1 2 3—4 2

rate of growth o f , 77—8 .

scars , 1 1 3 , (F ig .

sensitiveness o f , 74—7 .

sh edd ing of , 1 2 2 .

stoo l 1 2 1 —2 .

underground ,1 2 5

—4 0 .

work of , 74— 1 0 3 .

S ide-saddle Flowers , 36 5 .

S ieve-tubes , 69 , (Fig .

S i lene, 2 39 ,24 1 , 24 2 , 36 1 , 37 8 ,

S ilverweed , 379 .

S i symbrium, 37 8 , 38o .

Skeleton o f leaf , 6 5 , (Fig .

o f stem , 7 0 , (Fig .

S ku llcap ,Greater, 2 54 .

S leep-movements , 1 49 52

Smilax,1 47 , (F ig . 266 .

Snapdragon, 1 2 5 , (F ig . 2 56 ,

(F igSnowberry, 2 58 .

Snowdrop ,1 36 .

Snowflake ,267 .

Soc ial plants, 1 4 2 .

Soft-grass , 1 2 5 , 343. 348. 350So ils , 32 0 —36 .

aeration of , 33 1 . 335 , 37 2—3 .

37 5 °

calcareous, 33 1 .

capillarity of , 332—3 .

composition of , 32 1 .

e ffect o f hoeing , 334—5 .

humus-content, 322 .

liming , 332 .

organic matter in , 32 2 .

organisms in , 54—5 , 323

—6 .

permeability o f , 330 .

physiologically d ry , 336 .

properties o f , 32 8—3 1 .

salts in, 382 , 385 .

sedentary, 320 , (Fig .

transported , 32 1 , (F ig .

water-content , 32 2 .

water-supply , 335—6 .

So lanaceae ,2 54

—5 .

S olanum, 2 54—5 .

Solomon’s S eal, 1 28 , 266 , 349 .

S onchus , 37 8 , 379 .

Sorre l or Green-sauce , 380 .

sh eep’s , 369 , 379 .

Spath e ,1 96 , (Fig . 1 98 , (Fig .

1 36 )Spearwort, Lesser, 343, 37 0 , 376 .

Species , 1 1 , 2 3 1 .

Speedwell , Corn , 379 .

Germander, 1 83—5 , (Fig .

Ivy- leaved , 37 8 .

Marsh , 2 56 .

Water, 2 56 .

Spergu la , 2 39 .

Spergu lari a , 2 39 , 37 8 , 383 .

Spermaphyta , 2 3 1 , 2 33 .

Sphagnum bog , 396—7 .

Spind le Tree (Euonymus ) , 2 2 5 ,

Sp ines , branch , 339 .

leaf , 339 .

Spi raea ,2 43 .

Spi ranthes , 269 .

438 INDEX

Sweet-P ea , 29-

30 , 1 44 , 1 47 ,1 88

90 , (Fig . 2 27 , (Fig .

2 35 , 246 .

Sycamore ,1 1 2— I 4 , (Figs . 7 0

—1,

1 1 7 .1 2 0 ,

1 2 2,1 49 ,

2 1 41 5 , 22 2 , 30 3

—6 , (F ig .

SymbIOS IS , 35 5—6 .

Sympetalae, 2 32 ,248 .

Symphori carpus , 2 58 .

Symphytum, 2 5 0 .

Sympod ial branching , 1 1 9—2 1 .

Syncarpous , 1 7 ,1 7 I

Syngenesious , 1 7 8 , 26 1Sy ringa , 3 I 1Systematic botany, 2 29

—33

Tap roots ,1 2 , 58, (F ig .

Taraxacum, 380 , 385 .

Tare , 246 , 37 8 .

Tea-tree ,2 5 5 .

Tease] , 26 1 .

Temperature , effect onabsorption, 1 2 3 , 336 .

carbon-assimilation,84 .

d istribu tion, 3 1 5— 1 7 , 395 , 397 .

germination,transpirati on , 9 5 .

Tendrils , 30 , 1 44—7 , (Figs . 9 1

—4 ,

34 1 , (Fig .

Testa or seed - coat,2 1

,2 3 , 24 ,

2 8,

3 1 .

Teucrium, 2 54 .

Thali ctrum,2 37 .

Th istle , 2 1 4 ,2 2 2

,26 2 , 343, 348 ,

36 1 .

Field , 379 .

Marsh , 376 .

Sow , 37 8 , 379 .

Spear, 379 .

Thorn-apple , 2 5 5 .

Thyme, Wild , 2 52 , 36 1 , 37 0 .

Thymus , 2 5 2 .

Toadflax , Yellow,2 56 .

Ivy-leaved , 2 56 , 344 .

Toadstool , Su lphur-tu ft, 355 ,

(Fig .

Tobacco , 2 54 .

Tomato , 2 1 8 , 2 5 5 . Valerian,2 2 2 , 376 .

Toothwort , 343, 359 , (Fig . Vaccinium, 3 1 7 , 39 1 .

36 0 . Vascu lar bund les , 68—7 1 , (Figs .

3 1—40

Tragopogon , 379 . c losed and open , 7 0 .

Transpiration, 9 1 —5 .

amount of , 92 , (F ig .

c ircumstances favouring, 95 .

force of , 98 .

rate of , 94 , (Fig .

reduction of , 9 5 , 382 , 386 , 39 0 ,

39 5 0

su ction action of , 99 , (F ig .

Traveller’s Joy (see Clematis) ,1 64 . (F lg . 353 .

Trees , 1 0 6—2 2 , (Figs . 6 527 0

—3 1 4 , (Figs . 1 80

Trefo il , H op , 37 8 .

Tri ental i s , 2 50 , 353 .

Trifoli um, 246 , 37 8 .

Triglochin , 383 .

Trimorph ic flowers, 1 77 ,2 0 5 .

Tr i toma , 267 .

Tropophytes , 3 1 8 .

Tubers , root 60 , 6 2—4 , (Fig .

stem 1 2 8—3 1 , (F ig .

Tubu lar flowers , 1 7 1—9 2 , (Figs .

1 1 5- 1 8 , 1 2 0

Tubu liflorae , 262 .

Tu lip , 1 34—7 , (Figs . 85 2 0 7 ,

266 .

Tulipa , 266 .

Tunicated bu lb, 1 35 .

Tunics , 1 35 .

Turgid ity, 52 , 96—7 , (Fig .

Turnip, 59 , (Fig . 1 2 5 , 2 38 .

Tussi lago, 379 .

Tussocks,formationof , 367 , (Fig

2

Tway-blad e ,269 , 349 .

Twining stems, 1 42—4 , 34 1 .

c lockwise , 1 44 , (Fig . 34 1 .

contra- clockwise , 1 44,‘

(F ig .

34 1

Ulex,246 .

Ulmus , 29 5 .

Umbelli ferae , 246—8

, (Fig .

Umbels , 1 7 3 , 246 .

compound ,1 7 3

S imp le ,1 76 , (F i g .

Urti ca , 379 .

INDEX 439

V egetable Marrow , 2 8 .

V egetation , study o f , 3 1 5—2 0 ,

(Figs . 1 6 3 , 2 0 6 ,2 0 8

grass-lands , 366—7 0 , (Figs . 2 356

h edgerows , 336—44 , (Figs . 2 1 82 2 ,

meadows , 368—9 , (F i g .

moors , 390 —7 , (Figs . 2 50

mountains , 397—8 , (Figs . 1 63,2 0 6 , 2

pastures , 366—7 0 .

Ponds . 37 0—5 , (Figs . 2 38

salt-marsh es , 382—3 , (Figs .

2 1 1 ,

sand -dunes , 383—7 , (Figs . 80

1,2 1 0 , 246

sea-coast , 380 —9 0 , (Figs . 2 1 0 ,

2 1 1 , 24 5—9 )

sh ingle beaches , 387—9 0 , (F ig .

wood lands , 345 2 23

7Vegetative organs , 1 4 .

reproduction, 1 40—2 , 2 80 .

V eins (see V ascu lar Bund les) , I 4 ,

67 .

V enus’ F ly -trap , 1 5 2 , 366 , (F ig .

Verbascum,2 56 .

V ernal -grass , 2 0 1 , (F ig . 368 .

V ernation, 1 1 9 .

Veroni ca . 2 56 . 343. 37 8. 379 .

38 0 .

V erticillaster, 2 52 .

V etch ,1 44 ,

1 47 , 1 90 , 2 0 3 , 246 .

Bush , 34 1 , (Fig . 379 .

Horseshoe , 368 .

V etch ling , Yellow, 245 .

Vi burnum, 2 58 .

Vi ew,246 , 37 8. 379

V ine, 98 , 1 47 .

Vi ola , 378 .

V io let , 1 1 6 , 1 1 9 ,1 85

—6 , (Figs .

1 2 7 2 0 3 , 2 0 6 ,2 1 6 , (Fig .

2 27 , (F i g . 2 35 ,

343Dog , 353 .

Marsh , 348 .

Sweet , 1 86 .

Water, 249 .

Yellow , 37 0 .

V iper’s Bugloss , 2 50 , 379 , 389 .

V irginia Creeper, 1 0 8 , 1 44 , 1 47 .

,

(FigV i v1pary , 1 4 1

—2 .

Wallflower, 2 0 6 , 2 38 .

Walls , p lants o f , 344 .

Wall-rue (Asplen ium) , 344 .

Water, course o f , in stem , 89 .

need for . 49—50 . 5 5 . 9 5 . 97 .

1 0 2—3 .

pollen transferred by, 37 5 .

Water Buttercup , 37 1 , (Figs .

2 38 ,

Cress , 2 38 , 343 .

-cu ltures , 5 5—7 , (F i g .

-d ispersed fruits , 2 2 3—4 .

Lily.1 57 . (F ig 37 1 . (F ig .

weeds , 1 42 .

Water-plants , 37 0 —5 , (Figs . 2 37

aerati on i n, 37 2 .

flowers of , 37 5 .

invas ion by , 374 .

slime on, 37 3—4 .

struc ture of , 37 2 (Figs . 242

vegetative reproduction in,

3Water-stomata , 98 .

W ax on leaves , 9 5—6 .

Wayfaring Tree, 1 1 6 , 2 2 5 , 2 58 ,

Weeds , 376—80 , (Fig .

cornfield , 377—9 .

meadow and pasture , 379—80 .

Weigelia , 2 58 .

Wh eat , 30 — 2 , (Figs . 1 2 , 84 ,

97 , (Fig . 1 26 , 2 1 0 , 2 1 4 ,

26 5 .

Wh in, 39 5 .

P etty , 246 .

Whorl , 1 27 .

Wickens , 298 .

Wicks , 1 2 5 , 379 .

Willows, 1 2 1 , (F ig . 1 60 , 2 0 2 ,

2 0 4 , 2 2 1 , (Figs . 1 56 2 35 ,276

—8, (F ig . 294 , 348 ,

376 ;Creep i ng , 353 .

Dwarf , 386 .

Goat , 276 , 27 8 , (F ig .

P ollard , 277 .

Wh ite , 277 .

440

Willow-h erb , 2 2 1 , 379 .

Hairy, 376 .

Square-stemmed , 343 , 376 .

Wilting , 49 5 0 , 96 , 97Winged fruits , 24 , (F i g .

Winter Aconite ,2 38 .

Winter buds , 374 .

Wintergreen, Ch ickweed , 2 50 ,

3 53Woodbine , 2 58 .

Woodlands , plants o f , 345—54 .

Wood -rush , Field , 2 0 4 .

Woods , Alder-Carr, 353 .

Alder-Willow, 352 , 376 .

Ash . 349 . 35 3Beech , 35 3

—4 .

calcareous , 353—4 .

Oak-Ash , 353 .

Oak-B irCh -H eath , 3 52 .

P eduncu late Oak , 35 2 .

P ine , 352—3 .

S essile Oak , 347—5 2 ,

,

3 2 3—5 )

S i li ceous , 352—3 .

types of , 3 52—4 .

Wood Sorrel , 1 42 , 1 49—50 , (F ig .

(Figs .

INDEX

1 52 .1 54 .

2 0 4 . 2 2 8 . (Fig34 3 .

Woody Ni gh tshade , or Bi ttersweet , 1 1 6 ,

1 82— 3 , (F ig .

2 2 5 .

Woundwort, H edge , 2 54 , 343 .

Marsh ,2 54 .

Xerophytes , 2 52 , 3 1 8 , 382 , 386 .

Xylem , 69 .

Yarrow, 37 0 , 380 .

YellowRattle , 2 56 , 359 , 37 0 , 379 ,

380 .

Yew .1 9 8. 1 49 . (H g . 354 .

Yorkshi re F og , 368 , 37 0 , 380 .

Yucca ,266 .

Printed in England at the Oxford University Press

Z onation, 3 1 5in h edge

-bank, 337—8

, (Fig .

in water-plants , 37 2 , (Figs .

2 37Z ooph i lous , 2 0 5 .

Z ostera , 383 .

Z ygomorphi c ,1 7 3 .

Woodh ead,Th oma s Wi l l i am

Th e s t udy o f p l ant s

Forestry

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