Full text of "The study of plants; an introduction to botany and plant ecology"

See other formats

. .

►

u~)—

FACUL1

UNIVERSIlY OF IOaGNTO

THE

STUDY OF PLANTS

AN INTRODUCTION TO
BOTANY AND PLANT ECOLOGY

\J BY '

T. W. WOODHEAD, M.Sc, Ph.D., F.L.S.

LECTURER IN BIOLOGY
AT THE TECHNICAL COLLEGE, HUDDERSF1ELD

OXFORD
AT THE CLARENDON PRESS

1915

OXFORD UNIVERSITY PRESS

LONDON EDINBURGH GLASGOW NEW YORK

TORONTO MELBOURNE BOMBAY

HUMPHREY MILFORD M.A.

PUBLISHER TO THE UNIVERSITY

1296

PREFACE

The course of work followed in this book is directed,
in the main, to the establishment of the fundamental
principles of Plant Physiology. Plant Morphology
receives a less extended treatment ; but this aspect
of the subject is freely introduced in the discussion
of Plant Ecology, i. e. the relation of the structure
and functions of plants to their habitat. More space
has been devoted to Ecology than is usual in an ele-
mentary text-book, but the Author believes that this
aspect of plant life gives to field work a more definite
aim, and broadens the outlook of the student by linking
up Botany with the study of climate, geology, and
topography. Similarly, to avoid the weariness of
lessons dealing merely with the comparison of forms,
the Author has throughout treated the forms of roots,
stems, and leaves in relation to their functions and to
the habitat of the plant.

The plants selected for study are common species :
nearly all of them can be obtained from the fields,
hedgerows, and gardens, and it is expected that speci-
mens will be in the hands of students using the book.
The experiments suggested are usually so simple and
require such inexpensive apparatus that every pupil
in a class ought to be able to do them. Details 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. It is hoped

A 2

4 PREFACE

that the photo-micrographs and drawings in the book
will clear up any difficulties. They have been made
specially for this book, and are designed not as sub-
stitutes for actual specimens, but as aids to the
practical observation of plants.

Technical words have been introduced when necessary
for accurate description, but they have been avoided
whenever simpler terms were adequate. The common
as well as the systematic names of plants employed
in the book are to be found in The Botanist's Pocket
Book, by W. Hayward (thirteenth edition, revised by
G. Claridge Druce. Bell).

Although no particular syllabus has been followed,
the subject-matter covers the work necessary for
Matriculation, Senior Local Examinations, and the
Elementary Teacher's Certificate Examination ; with
suitable omissions, the book can also be used for
Preliminary and Junior Local Examinations and for
Scholarship Examinations for entrance into Secondary
Schools.

The Author records his obligations to Miss M. M.
Brierley for the great care and interest which she has
taken in the preparation of the illustrations, and for
help in many ways ; to Miss H. Rigby for some of the
drawings ; and to Mr. A. W. Sykes, Mr. W. H. Sikes,
Miss H. M. Sikes, and the late Mr. H. G. Brierley, for
many of the photographs. To Miss D. Ventham, M.A.,
Miss E. M. Poulton, M.Sc, and especially to the
Rev. T. A. Jefferies, F.L.S., he is indebted for many
helpful criticisms.

CONTENTS

PAGE

PART I. THE VEGETATIVE ORGANS
CHAPTER I

THE GARDEN STOCK

The organs of a plant ; roots, stems, leaves, flowers, fruits,
and seeds . . . . . . . . .it

CHAPTER II
STRUCTURE AND GERMINATION OF SEEDS

(a) Dicotyledons : Bean, Pea, Sunflower, Ash. Germination.

(b) Monocotyledons : Wheat, Maize, Oat, Onion, Wild
Hyacinth, Germination . . . . . . .19

CHAPTER III

STRUCTURE OF ROOTS

The tissues of a root. Epidermis, root-hairs, cortex ; stele,
vascular bundles, bast, cambium, and wood. Their arrange-
ment in a young root. Structure of old roots ; cork. Roots of
Monocotyledons ........ 34

CHAPTER IV

WORK OF THE ROOT

Sensitiveness of the root. Geotropism. Sensitive region of
the root. Hydrotropism. Negative heliotropism. Respira-
tion. Regions of growth and curvature of the root. Origin of
root-branches. Growing-region of the stem. Root-hairs, their
structure and use ; the root-cap. Excretion by roots. Osmosis.
Water-cultures ........ 37

CHAPTER V

FORMS OF ROOTS

Tap-roots and adventitious roots. Roots as storage organs.
Climbing, aerial, and aquatic roots. Suckers from roots.
Root-tubers of the Lesser Celandine . . . . -58

CONTENTS

PAGE

CHAPTER VI

STRUCTURE OF THE SHOOT

The environment of the root and shoot. Dissection of a leaf.
Epidermis, stomata, skeleton, green tissue. The tissues of
a stem. Mechanical supporting tissues. Vascular bundles.
Annual rings. Cork. Separation-layer of the leaf. Leaf -fall 64

CHAPTER VII

WORK OF THE SHOOT

Sensitiveness of the shoot. Negative geotropism. Force
exerted by the growing shoot. Heliotropism. Etiolation.
The work of the leaf. Photosynthesis ; the formation of starch.
Chlorophyll. Functions of the vascular bundles. Crude sap
and elaborated sap. Storage of food ..... 74

CHAPTER VIII

WORK OF THE SHOOT (continued)

Transpiration. The Potometer. Protection of stomata.
Wilting. Turgidity. Root-pressure. Force of transpiration.
Air-channels in a shoot . . . . . . 91

CHAPTER IX

BUDS AND BRANCHES

The development of shoots. The Brussels Sprout. Branching.
Leaf rosettes. Lilac, Privet, Horse-Chestnut. Sycamore.
Beech. Pine. Dormant buds. Stool shoots. Adventitious
buds. Shedding of leaves and branches . . . .103

CHAPTER X

HIBERNATION ; THE STRUCTURE OF MODIFIED

SHOOTS

Annuals and Ephemerals. Biennials. Perennials. Rhizomes.
Tubers. Corms. Bulbs. Contractile roots. Droppers.
Elongated bulbs. Vegetative reproduction . . . .123

CHAPTER XI

MOVEMENTS AND ATTITUDES OF PLANTS

Nutation. Twining plants. Tendrils. Sun and shade positions
of leaves. Phyllodes and phylloclades. Leaf-mosaics. Sleep-
movements of leaves. Movements of flowers and fruits . 142

CONTENTS 7

PAGE

PART II. THE REPRODUCTIVE ORGANS

CHAPTER XII

BIOLOGY OF THE FLOWER. DICOTYLEDONS

I. Pollination of Simple Flowers by Wind and Insects

Structure and functions of the flower. Sepals, petals, stamens,
carpels. Wind-pollinated flowers. Self-pollination. Insects
as pollinators. Mouth-parts of insects. Pollen-flowers. Peri-
gynous and epigynous flowers ; the flower-tube. Devices to
secure cross-pollination . . . . . . .156

CHAPTER XIII

BIOLOGY OF THE FLOWER (continued)

II. Pollination of Tubular and highly developed Flowers

Dimorphic, trimorphic, and cleistogamous flowers. Irregular
bee-flowers. Summary of the chief types of flower-structure
in Dicotyledons . . . . . . . .174

CHAPTER XIV
BIOLOGY OF THE FLOWER (continued)

Monocotyledons

Simple trimerous flowers. Complex irregular flowers of Iris
and Orchis. Grass flowers. Summary of flower-structure in
Monocotyledons . . . . . . . .194

CHAPTER XV

POLLINATION, FERTILIZATION, AND THE ORIGIN OF

SEEDS

The chief methods of pollination. Nectaries. Structure of the
pistil and ovules. Fertilization. Changes resulting from
fertilization 203

CHAPTER XVI

STRUCTURE OF FRUITS

Dry fruits : {a) Indehiscent : Nuts, achenes, samaras, and
cremocarps. (b) Dehiscent : Follicles, legumes, siliquas, and
capsules. Succulent fruits : Drupes, berries, pomes, and com-
pound fruits . . . . . . . ..211

8 CONTENTS

PAGE

CHAPTER XVII

DISPERSAL OF FRUITS AND SEEDS

Colonization of a barren island by plants. Means of dispersal

by wind, water, animals, and propulsive mechanisms . .219

PART III. SYSTEMATIC BOTANY

CHAPTER XVIII
CLASSIFICATION OF PLANTS

History of systematic botany. The chief divisions of Flower-
ing Plants. The study of a local flora .... 229

CHAPTER XIX

DICOTYLEDONS : A. ARCHICHLAMYDEAE

Natural orders : Salicaceae ; Betulaceae ; Fagaceae ; Ranun-
culaceae ; Cruciferae ; Caryophyllaceae ; Rosaceae ; Papi-
lionaceae ; Umbelliferae ....... 234

CHAPTER XX

DICOTYLEDONS : B. METACHLAMYDEAE

Natural orders : Primulaceae ; Boraginaceae ; Labiatae ;
Solanaceae ; Scrophulariaceae ; Caprifoliaceae ; Compositae 248

CHAPTER XXI

MONOCOTYLEDONS

Natural orders : Gramineae ; Liliaceae ; Amaryllidaceae ;
Iridaceae ; Orchidaceae ....... 264

PART IV. COMMON TREES AND SHRUBS

CHAPTER XXII

CONE-BEARING TREES

Scots Pine and Larch ....... 270

CHAPTER XXIII

CATKIN-BEARING TREES

Willow, Poplar, Hazel, Birch, Alder, Beech, and Oak . . 276

CONTENTS 9

PAGE

CHAPTER XXIV

TREES WITH MORE HIGHLY DEVELOPED FLOWERS
Elm, Rowan, Laburnum, Sycamore, Horse-Chestnut, Common
Ash, and Lilac ......... 295

PART V. ECOLOGY
CHAPTER XXV

PLANT HABITATS AND COMMUNITIES
Types of Vegetation. Plant formations, associations, and
societies . . . . . . . . . • 3X5

CHAPTER XXVI
THE SOIL
Origin of soils. Sedentary and transported soils. Composition.
Organisms in the soil. Properties. Siliceous soils. Sand, clay,
subsoil, humus, and peat. Calcareous soils, liming, hoeing.
Water supply . . . . . . . • 32°

CHAPTER XXVII

PLANTS OF HEDGEROWS AND WALLS
Uses and distribution of Hedgerows. Plants of the hedgebank,
ditch, and sward. Trees and Shrubs. Climbing plants.
Herbaceous species. Walls . . . . . -336

CHAPTER XXVIII

WOODLAND PLANTS
Features to observe in the study of a wood. Dry and moist
woods on siliceous soils. Ash woods on calcareous soils.
Plantations. Complementary societies. Types of British
woodland ......... 345

CHAPTER XXIX
PLANT-LIFE IN HUMUS
Abnormal modes of nutrition. Saprophytes. Mycorrhiza and
symbiosis. Parasites. Insectivorous plants . . .354

CHAPTER XXX

GRASS-LANDS : PASTURES AND MEADOWS
Pastures and meadows. Grass moors. Calcareous and
neutral grass-lands. Survey of a pasture .... 366

io CONTENTS

PAGE

CHAPTER XXXI

WATER AND MARSH PLANTS

The vegetation of a pond. Structural peculiarities of water-
plants. Invasion. Marsh-plants . . . . . 370

CHAPTER XXXII

WEEDS

Weeds of cornfields, meadows, and pastures . -376

CHAPTER XXXIII
VEGETATION OF THE SEA-COAST
Seaweeds. Salt-marshes, sand-dunes. Strand -plants. Shingle
beaches .......... 380

CHAPTER XXXIV

MOORLAND AND ALPINE PLANTS

Cotton-grass moors. Heather moors. The Sphagnum bog.
Alpine plants ......... 390

EXAMINATION PAPERS 400

INDEX 421

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 the
soil ; and (3) to notice how they are related one to the other,
and their uses to the plant. It is necessary to describe the
structures 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, examine it carefully,
and draw the parts you see. Two regions are at once

1 The plants from which the chief garden Stocks have been
derived by cultivation and selection are known to botanists as
Matthiola incana, M. annua, and M. sinuata. Plants which have
come from one parent or one kind are said to belong to one species.
Thus the Queen Stock belongs to the species incana ; the Ten-
weeks' Stock belongs to the species annua. Both these, however,
agree in many important details of structure, and are therefore
grouped together under one genus, Matthiola. Each plant-name
thus consists of two words, a substantive or generic name, and
an adjective or specific name. The generic name, Matthiola, was
given to the Stock by Robert Brown, in honour of the Italian
botanist. Mattioli (1501-72).

12 THE VEGETATIVE ORGANS

recognized : (A) a part which grows downwards into the
soil, and (B) a part which grows upwards into the air and is
green. The former we may call the descending axis or
root. This consists of a main tapering root called the
tap-root (often distorted in cultivated plants) which gives
off numerous branches growing obliquely downwards.
These in turn produce branches which are white, and on the
younger parts minute root-hairs are developed. The root-
hairs are almost too small to be seen with the naked eye,
and are generally broken off in digging up the plant. At
the end of each root-branch is the growing-point; covered
by a protective root-cap. The older root-branches are
brown, being covered with a layer of cork, and are unable to
absorb water.

The part of the plant above ground is the ascending
axis, and consists of organs of two kinds : (i) a stem
which is erect, cylindrical, strong, and somewhat woody
below ; more tender, slightly ridged, and green above, with
a grey covering of branched hairs. A tender green stem
is said to be herbaceous. From this arise (2) thin, flat
leaves (Fig. 1,/). In the angle or axil between the leaf
and 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 young
leaves of the bud. In older plants the leaves have fallen
from the lower part of the stem, leaving scars (s) on the
surface. The base or region of attachment of a leaf is
somewhat enlarged, and this passes imperceptibly into
the blade without a definite leaf -stalk or petiole. The
shape of the blade is oblong-lanceolate with an even or
entire margin ; and the apex is bluntly pointed or some-
times rounded. Like the stem, the leaf is covered with
branched hairs. Running through the leaf from base to
apex is the midrib, which gives off a branching network of

Fig. i. The Stock Plant. — a, the root system; b, the shoot
system ; b, axillary branch ; /, foliage-leaf ; fl, flower ; fr, young
fruit ; g, ground level ; p, pedicel ; s, leaf-scar.

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 stem
and the way in which they are related one to another.

Perform the following experiment : Tie one end of
a piece of thread round the base of a leaf ; then wind the
thread round the stem from right to left in such a way that
it touches the base of each leaf in turn as it ascends.
Eventually you will meet with a leaf standing vertically
above the one with which you began. Count the leaves
passed by the thread, omitting the first, and determine the
number of times the thread has passed round the stem.
Commonly you will find that the spiral goes
twice round the stem and touches five
leaves ; thus we see that the leaves are
arranged spirally on the stem, and each is
separated from the one above or below it
by two-fifths of the circumference (Fig. 2).
Exceptions to this arrangement are not
uncommon in the Stock. The same test
might be applied to other plants, e. g. :
Groundsel, Oak, Deadnettle, Elder; and
Hazel. The arrangement of leaves on a
stem is called phyllotaxy (Gr. phyllon =
leaf, tasso = arrange), and is usually such
the leaves in a favourable position with

iC^I

Fig. 2.
Diagram of

Leaf
Arrangement.

as to place
regard to sunlight.

The three structures— root, stem, and leaf— are con-
cerned with the growth of the plant, and are hence known
as 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 flowering
shoots form the inflorescence. Notice that in either

THE GARDEN STOCK

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 arises
independently 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

3UJ 4

Fig. 3. Dissection of a Stock Flower. — 1, Vertical section
01 flower ; 2, petal removed ; 3, stamen removed ; 4, transverse
section of ovary; 5, pistil; a, anther; cl, claw; /, filament;
g, pistil; k, calyx; I, limb; n, nectary; 0, ovary; ov, ovule;
p, petal ; pi, placenta ; r, receptacle ; re, replum ; s, stamen ;
st, stigma ; sy, style.

before you so as to show their interrelations. The portion
of the stalk on which these parts are borne is called the
receptacle (Fig. 3, r). On the outside are four erect distinct
green leaves ; these are called sepals, and together form the
calyx (k). They serve to protect the inner parts when the
flower is in bud. When the sepals of a calyx are distinct
or free one from another, the calyx is said to be polyse-
palous (Gr. polys = many). Note that two of the sepals

16 THE VEGETATIVE ORGANS

are bulged or saccate at the base. Now press the flower
backwards against the stem and determine whether these
two sepals stand right and left, i. e. are lateral with refer-
ence to the stem ; or are anterior and posterior. These
sepals, though apparently lower, are fixed a little higher on
the receptacle than the other two. Now notice the next
four inner leaves, the petals. These, like the sepals, are
free from one another and form the corolla, which is
therefore polypetalous. The petals alternate 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 the
sepals, then spreads out at right angles as a broad, white or
highly coloured, thin blade, known as the limb (/). Further
inwards, and higher on the receptacle, are the stamens (s),
six stalked bodies together forming the androecium
(Gr. aner, a ndros = man, oikos = house). Each stamen
consists of a stalk or filament (/) bearing a two-lobed
yellowish body termed the anther (a), and each lobe con-
tains two parallel chambers called pollen-sacs filled with
minute bodies known as pollen-grains. The stamens are
not all alike : two are short and lateral in position, fixed
a little lower on the receptacle than the remaining four
longer ones, which are in two pairs, anterior and posterior.
Examine the base of each short stamen and you will find
on the inner side two swellings, known as nectaries («),
which secrete honey. The bulged sepals provide accom-
modation for these. When sepals, petals, or stamens are
free from and arise below the pistil they are said to be
hypogynous (Gr. hypo = under, gyne — female).

When the stamens are removed we find in the centre
of the flower an elongated green body, the pistil or
gynoecium (g). All the other parts — sepals, petals, and
stamens — stand below, i. e. are inferior to this. In other
words, the pistil stands highest on the receptacle and is

THE GARDEN STOCK

therefore superior to the other parts of the flower. If the
pistil be cut across (Fig. 3, 4) and examined by the aid of a
pocket lens, it will be seen to consist of two chambers, each
containing two rows of minute bodies called ovules (ov).
The structure from which the ovules arise is called the
placenta {pi), and the ovule-bearing part of the pistil is
known as the ovary (5 0). On the top of the ovary is
a very short neck — the style (sy), terminating in a
two-lobed structure — the stigma (st). The pistil may
thus be seen to consist of
two bodies fused together ;
these are called carpels.
When two or more carpels
are united, the pistil is said
to be syncarpous (Gr. syn
= together, karpos = fruit).
These organs are called floral
leaves ; the sepals and petals
are leaf-like, but the stamens
and carpels bear little resem-
blance to leaves. Fig. 4 is
a plan showing the relative
positions of the parts. Such
a plan is known as a ' floral
diagram '.

In the lower, older part of the inflorescence it will be
noticed that all the parts of the flower have fallen off, with
the exception of the pistil, and that this has grown enor-
mously to form a long narrow fruit (Fig. 1, fr). Select a
mature fruit and dissect it (Fig. 5). Remove the two side
lobes, which separate easily from the base upwards. It
will then be found that a frame is left, called the replum (re) ,
with a thin membrane stretching across it. Attached to
the frame by slender stalks are the flattened seeds (sd),
each surrounded by a thin wing. The wall of the ovary,

1296 R

Fig. 4. Floral Diagram. —
a, anterior ; g, pistil ; k, sepal ;
/, lateral ; p, petal ; Pr, poste-
rior ; s, stamen ; x, axis.

THE VEGETATIVE ORGANS

which forms the coat of the fruit, is called the pericarp
(Gr. peri = around) .

The flowers of Stocks are often sweetly scented, especially
at night. This attracts night-flying moths, which visit the
flowers and search for the pollen and honey. In the process
they become dusted with pollen, and, carrying it to other
Stock flowers, may deposit grains on the stigma and thus

Fig. 5. Dehiscent 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 of
a plant are of two distinct kinds, (1) vegetative organs —
roots, stems, and leaves — which are concerned with obtain-
ing food and building up the main body of the plant ; and
(2) reproductive organs — the flowers — whose function is to
produce seed, from which arises a new generation of plants.

STRUCTURE AND GERMINATION OF SEEDS

CHAPTER II
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 Pod. — 1, side view ; 2, pod opened along
the inner or ventral suture ; fu, funicle ; k, calyx ; p, placenta ;
st, stigma.

they perform their twofold function, (1) in helping to
sustain 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.
Pod and seeds of the Bean. — The Broad Bean provides

b 2

THE VEGETATIVE ORGANS

us with excellent material, and we will begin with the Bean-
pod (Fig. 6, i). This is a fruit derived from the pistil of the
Bean flower, but, unlike the Stock fruit, 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), and
often parts of the stamens are to be seen. The ovary has

Fig. 7. Dissection of the Bean Seed. — 1, seed with funicle
attached ; 2, end view of seed ; 3, dry seed ; 4, partly soaked
seed ; 5, concave edge of seed ; 6, testa showing entrance to radicle
pocket ; 7, radicle pocket in side view ; 8 and 9, cotyledons separated ;
c, cotyledon ; fu, funicle ; h, hilum ; m, micropyle ; pi, plumule ;
ra, radicle ; r.p, radicle pocket ; t, testa.

enlarged greatly, and now contains the seeds, or beans as we
call 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 (2), we find it is to this edge that the seeds are
attached. The seed-stalk or funicle (fu) is curious;
it grows from the edge or placenta (p) of the carpel, and
it enlarges into a much-thickened body clasping the seed.

STRUCTURE AND GERMINATION OF SEEDS 21

Remove a seed (Fig. 7, 1). Notice that it is flattened and
oval ; one edge is convex and the other slightly concave ;
it is covered on the outside by a thick, tough, light-brown
skin — the testa (6 1) ; and when the seed-stalk or funicle (fu)
is removed, a scar or hilum (2 h) is left, indicating the point
of 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
(4), then the seed swells so much that the skin is
tightly stretched, and if it be squeezed laterally, a little
drop of water will be seen to ooze out from a small hole
— the micropyle (Gr. mikros = small, Pyle = 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 hole
represents the micropyle of the ovule, through which the
pollen-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 the
concave edge ; find the little pocket and determine its use
(6 and 7 r.p). The structure enclosed by the skin consists
of two large fleshy lobes — the seed-leaves or cotyledons
— (8 and 9 c), and between these is a bluntly-pointed struc-
ture— the radicle (8 ra), the tip being directed towards
the micropyle. The pocket in which it rested is called
the radicle pocket.

Separate the two cotyledons and look for the young,
curved shoot, bearing tiny leaves at its tip. This is the
plumule (8 pi). Between the plumule and the radicle
thick stalks are given off to the cotyledons. These struc-
tures— the two cotyledons, radicle, and plumule — form
a young, dormant plantlet called the embryo.

Compare the pod and seeds of the Garden Pea or the

THE VEGETATIVE ORGANS

Sweet-Pea with those of the Bean. What are the most
important points of agreement or difference ?

Food stored in the cotyledons. — Seeds like the Garden Pea
and the Bean are common articles of food. In what
does the nutriment consist, and where is it contained ?
An instructive, though only partial, answer is easy to find.

Place a little powdered laundry starch in a test tube,
add water, and boil for a few minutes. Allow it to cool,
add a drop of iodine solution,1 and note the dark violet

Fig. 8. Fruit of Sunflower. — i, side view ; 2, fruit opened
and one cotyledon removed ; c, cotyledon ; fu, funicle ; pe, peri-
carp ; pi, plumule ; ra, radicle ; sc, scar ; /, testa.

colour produced. Repeat the experiment with flour, and
a slice of potato ; the same violet coloration is seen.
This coloration indicates the presence of starch ; in other
words, the addition of a solution of iodine to a starch-
containing substance produces a violet coloration. Now
take a cotyledon of the Bean and place a drop of iodine
solution on its uninjured surface. Scratch the surface of
another cotyledon, add iodine solution to the scratched

1 A solution of iodine and potassium iodide 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 the
Bean and Pea contain much starch, and it is chiefly this
which gives them their value as food.

The seeds of the Bean and Pea agree closely in their
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 fruits, e. g. those
of the Sunflower (Fig. 8, 1). Here we find a triangular
fruit with a narrower end, which was attached to the
receptacle, and also a broader end on which is a scar (sc),
left when the corolla and style dropped off. The outer
ribbed 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 the
seed to the pointed end of the fruit. Remove the seed-
coat and examine the embryo, noting the radicle (ra) at
the pointed end and the two flat cotyledons (c), between
which is the small plumule (pi). Test the cotyledons
with iodine solution : do they contain starch ? If a thin
section, treated with iodine solution, is examined under the
microscope, the cells will be seen to contain a number of
small yellowish granules. These are protein or nitro-
genous bodies called aleurone grains (similar 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 section is placed for
a while in ether the globules dissolve ; also, if a drop of
1 per cent, solution of osmic acid is placed on another
section, the globules stain a blackish brown. These tests
prove that the cotyledons contain protein or aleurone
grains and much fatty oil. Oil is a common storage
material in seeds, and often replaces starch.

Endosperm. Food stored outside the embryo. — The Ash

THE VEGETATIVE ORGANS

fruit (Fig. 9, i) is a different type. Examine its curious,
slightly-twisted, and winged fruit-case (i), which is swollen
at one end and contains a single seed. Cut open the fruit-
coat (2 pe) and notice the mode of attachment of the
seed (2 ju) ; then remove the seed-coat and examine
the contents. Split open the seed, and between the two
flat lobes you will find the embryo, consisting of a radicle
(2 ra), above which are the two cotyledons (2 c), having

Fig. 9. Fruit of Ash. — 1, side view ; 2, fruit opened and seed
dissected ; c, cotyledon ; e, endosperm ; ju, funicle ; pe, pericarp ;
ra, radicle ; /, 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, s per ma = seed) .

Plants similar 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

STRUCTURE AND GERMINATION OF SEEDS 25

determine the uses of the structures found in a Bean seed.
Soak a number of dry seeds in water for a day, and then
sow several in a pot of damp coco-nut fibre, sand, or saw-
dust. In a few days remove some of them carefully,
allowing the rest to continue their growth. Note what
has happened. Which structure is the first to emerge from
the seed — radicle or plumule ? As the radicle emerges you
will see that it bursts through the skin near the micropyle.
Later on, look for the plumule as it pushes its way through
the soil. Of what form is it ? Do you see any advantage
in this mode of emergence ?

At the end of the crook-like plumule note the tender
young leaves, observing that they are carried upwards
as the stem grows, with little risk of injury, and that when
well above the surface the plumule grows more quickly on
the under side than on the upper, and so straightens itself.
The leaves expand, new ones appear in succession, and in
time buds form in their axils, which grow into leafy shoots
similar to that from which they spring. In cases where
the plumule has been injured, note that buds arise in the
axils of the cotyledons.

Although a seedling is able to obtain little or no food
from the coco-nut fibre, sawdust, or sand, for some time
it continues to grow vigorously, increasing its roots and
enlarging its stem and leaves. Upon what is the plant
feeding ? Where does the material come from ? If we
examine an older Bean seedling, we find that the cotyledons
remain below ground and do not emerge from the seed-
coat, but gradually lose their contents and shrivel up as
the plant grows : i.e. the cotyledons, at first swollen with
starchy and other food, provide the materials upon which
the seedling feeds and grows in the earlier period of its life.

In the Kidney-Bean or Scarlet -Runner the cotyledons,
though fleshy, come above ground and turn green (Fig. 10).

Hypogeal and epigeal germination. — Sow seeds of Mustard

THE VEGETATIVE ORGANS

and Cress on damp blotting-paper or flannel, covering them
with a jar to keep the air around them moist, and note the
mode of emergence of radicle and plumule ; observe also

9 ^* 9

Fig. io. Seedling of Kidney-Bean.
g, ground level ; c, cotyledon.

how the cotyledons are folded, and that they come above
ground, turn green, and, while simple in the Mustard,
(Fig. ii, 1-5), they are three-lobed in the Cress, a rather

STRUCTURE AND GERMINATION OF SEEDS 27

unusual occurrence (6). As the roots of these seedlings
grow they become covered with a rich crop of root-hairs
(r.h). Notice carefully how they are distributed, and from
what part of the root they are absent.

Seeds of the Edible Pea, Sweet-Pea, Vegetable Marrow,

Fig. 11. Seedlings of Mustard and Cress. — 1, section of
Mustard-seed showing the folded cotyledons ; 2, 3, 4, and 5, different
stages in germination of Mustard-seed ; 6, Cress seedling ; 7, root-
hair, magnified ; c, cotyledon ; c.w, cell-wall ; e, epidermal cell ;
hy, hypocotyl ; n, nucleus ; P, protoplasm ; pi, plumule ; r, section
of radicle ; ra, radicle ; r.h, root-hair ; s, seed ; s.r, secondary root ;
/, testa.

fruits of the Sunflower, Common Ash, Sycamore, and Oak,
should be germinated in the same way and their modes of
growth compared. In the case of the Sunflower (see
Fig. 22), note that when the radicle emerges, the fruit-coat
splits into two halves along the edge and, unlike the Bean,

28 THE VEGETATIVE ORGANS

the stalk below the cotyledon (hypocotyl, Fig. u, hy)
grows in such a way as to bend in the form of a crook and,
continuing to elongate, carries the cotyledons and the split
fruit-coat above ground. The cotyledons now separate,
throw off the fruit- and seed-coats, and turn green.

Seeds of the Vegetable Marrow should be sown with
their flat faces horizontal ; in a few cases cut away a third
of one side of the seed-coat at the micropylar end and sow
these with the cut surface downwards, and determine the
mode of emergence of the plumule in each case, and note
how it separates from the seed-coat. As the radicle
emerges and turns downwards from the uninjured seeds,
a peg is formed on the under side, at the base of the hypo-
cotyl, which fixes the lower edge of the split seed-coat and
holds it down. The hypocotyl above elongates, the upper
half 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 of
the seed-coat has been removed, the peg is unable to act
as holder, and the cotyledons, unable to extricate them-
selves, 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 free
themselves more readily from the seed-coat. The position
of the peg is always on the under side, and, like the down-
growth of the radicle, is determined by gravity.

Two modes of germination are seen in these types. In
the Bean, Edible Pea, and Sweet-Pea, the seed remains
below ground and only the plumule grows into the air ; this
mode of germination is known as hypogeal (Gr. hypo
= beneath, ge = earth). In the Kidney-Bean, Mustard, Cress,
Sunflower, Vegetable Marrow, Common Ash, and Syca-
more, the part of the stalk below the cotyledon (the hypo-
cotyl) grows and carries the cotyledons and plumule
together into the air. In these cases the cotyledons turn

STRUCTURE AND GERMINATION OF SEEDS 29

green and act as the first green leaves. This mode of
germination is called epigeal (Gr. epi = upon).

Allow the seedlings to continue their growth, compare
the successive leaves as they appear, and note that the first-
formed foliage -leaves are often simpler than the later ones.
In this respect the Sweet -Pea is an interesting example
to study.

Development of the Sweet-Pea. — Sow a few seeds in soil
and allow them to grow for several weeks, supporting the
tender stems with thin sticks. Note carefully each leaf
as it appears until the fully-matured ones are formed.
Compare the first or ' juvenile ' foliage-leaves with the later
adult leaves and try to determine the structure and uses
of the parts.

As the arched shoot comes above ground (Fig. 131, 5,
p. 189), very small leaves appear ; the first is seen to consist
of two pieces or lobes, with a narrow pointed lobe between
them (Fig. 131, 6, t) ; the second leaf is a little larger, and
the lobes are better developed and toothed (Fig. 131, 7) ; the
third leaf still shows the two lobes close to the stem ; and
above these is a short leaf-stalk, then a pair of oval lobes, be-
tween which is a slender green thread (Fig. 131, 8). The two
lower lobes, or stipules (st), are outgrowths of the leaf -base;
they cover and protect the rest of the leaf in the bud. The
leaf-stalk and blade are represented at first only by the
narrow terminal lobe ; in the later leaves the blade develops
two large opposite lobes, and the terminal thread becomes
longer. Finally, the terminal part of the blade divides
to form paired structures agreeing in position with the
lobes of the blade, of which they are special modifica-
tions. Note their behaviour on coming into contact with
a stick, and you will see at once the use of this curious
modification as a clinging organ. In the older plant (Fig.
131, 1) these organs are well developed, and by twining
round a support enable the stems to grow up above

THE VEGETATIVE ORGANS

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 erect
position. In some plants, however, tendrils are formed
from organs other than leaflets.

a.r

Fig. 12. Grains of Wheat and Maize. — i, grooved surface ;
2, convex surface of Wheat grain ; 3, 4, and 5, stages in germina-
tion of Wheat grains; 6, germinating grain of Maize ; a.r, adven-
titious roots ; em, embryo ; /, foliage-leaves ; PI, plumule ; ra,
radicle ; r.c, root-collar ; r.h, root-hair ; sh, colourless sheath.

(b) Monocotyledons

The Wheat grain. Embryo with one cotyledon ; the endo-
sperm.— Soak a few grains of Wheat in water for a day ;
then place some of them in a jar lined with wet blotting-

STRUCTURE AND GERMINATION OF SEEDS 31

paper, and others in coco-nut fibre. Compare dry and
soaked grains as to size and shape. A grain of wheat
(Fig. 12) 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 easily distinguished. The outer
fruit-coat, or pericarp, is smooth, grooved on one side
(Fig. 12, 1) and convex on the other (2). Note the tuft of

Pi.

ep.

Fig. 13. Vertical Section of Wheat Emeryo. — a.r, adven-
titious root ; e, endosperm ; ep, epithelium of the scutellum ; /,
ligule ; PI, plumule ; ra, radicle ; r.c, root-collar ; sc, 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 along
the groove and apply a drop of iodine solution to the cut
surface. 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.

32 THE VEGETATIVE ORGANS

A section of the embryo is shown in Fig. 13. Below is the short
radicle (ra) ; above is the straight plumule (pi). On one
side is a shield-shaped structure, the cotyledon or scutel-
lum (sc), with its convex face applied to the starchy food-
reserve ; and opposite the point of attachment of the shield
is a tiny scale, the ligule (/).

The Wheat grain thus consists of a fruit-coat and seed-
coat fused together, an embryo consisting of a radicle,
a plumule, a single cotyledon (the scutellum), and a
ligule ; and, occupying the larger part of the grain, is the
food-reserve, which is outside the embryo and therefore
called endosperm (e). (Compare this with the fruit of the
Ash, Fig. 9.)

Plants which contain only one cotyledon in the embryo
are placed in a large class called Monocotyledons.

Germination of Wheat and Maize. — Examine germinating
grains in different stages of growth, and note the behaviour
of the parts of the embryo (Fig. 12, 3, 4, and 5). As the
radicle (ra) elongates, it bursts through the thick tissue
which surrounds it, and now encircles its base as a root-
collar (r.c). Continuing to grow, it becomes clothed with deli-
cate root-hairs (r.h) everywhere except at the tip. Look
for the root-branches (a.r) and determine their point of
origin. Note that some spring from the base of the stem.
Roots arising from the stem are called adventitious roots
(Fig. 12, 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 the main
root : the fibrous roots of the mature plant all arise from
the nodes of the stem.

Compare the mode of emergence of the plumule (pi) with
that of the Bean and other seedlings examined, and note
the differences. In the Wheat the leaves are rolled up and
enclosed in a smooth, colourless, tubular leaf, the whole
forming a compact structure well adapted for boring its

STRUCTURE AND GERMINATION OF SEEDS 33

way upwards and uninjured through the soil. Examine the
grain of an older seedling (Fig. 12, 5) and note the changes
that have occurred. It is no longer a firm, solid mass, but
has become wrinkled ; and
when squeezed, readily col-
lapses, ejecting a milky-
looking fluid.

As the green foliage-leaves
grow they push their way
out of the colourless sheath
(Fig. 12, sh) and unroll.
Soon a drop of water appears
on the tip of each leaf.
Where has this come from ?
Considering the conditions
under which the seedlings
have been grown, do you
think they are drops of
dew ? As the drops dry off,
note that a whitish deposit
is left. Is such a deposit
left when dew-drops evapo-
rate ? Note that such drops
occur freely when the seed-
lings are well supplied with
water. The root-hairs and
young roots absorb more
than the plant is able to
use, and the excess exudes
from pores at the leaf-tips.

Fig. 14. Vertical Section of
Maize Grain. — a.r, adventitious
root ; e, endosperm ; ep, epi-
thelium of the scutellum ; PI,
plumule ; ra, radicle ; r.c, root-
collar ; sc, scutellum ; st, stigma.

This water contains mineral

salts in solution, and when the exuded drops evaporate,

the salts remain as a powder on the leaf-tips.

Grains of Maize (Fig. 12, 6 and Fig. 14) and Oat should
be treated in the same way as the Wheat, and their parts

1296

34 THE VEGETATIVE ORGANS

compared. In the Maize, note the smooth pericarp, and
the remains of the stigma as a little point above the embryo
(Fig. 14, st), also the hard endosperm (e). A germinating
grain is shown in Fig. 12, 6. The Oat differs from the
Wheat and Mai2e in that the grain is covered with chaffy
scales. Other interesting examples belonging to the same
class are the Onion and the Wild Hyacinth. In these the
tip of the cotyledon remains in the endosperm and acts as
a 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 in
length 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 very
many years ; but under the conditions we have provided
— viz. moisture, air, and warmth — germination begins.

CHAPTER III

STRUCTURE OF ROOTS

Tissues of a mature dicotyledonous root. — We have seen
how roots arise, also their form and mode of growth ; let us
next consider how roots are constructed. Fig. 15, 1 is
a photo-micrograph of a cross-section of an old root of a
Dicotyledon showing the different tissues of which it
is composed. The outer surface is composed of a layer
of cells called the epidermis (e) (Gr. epi = upon, derma
= skin). In the young root some of these cells grow out to
form root -hairs (see Fig. II, 7). Beneath the epidermis is
a wide ring of cellular tissue — the cortex (Fig. 15, co) with
small air-spaces between the cells. The innermost layer of

ct5
o

<J"

X
D

ct5

"?r

-O

■ —

-o

-a

O
O

<4H

•

„ — s

O
O

3
O

• •«

i-i

—

"c3

Z-,

t/3

* *■

4-1

+->

u-i

■ *

—

><e

-M

STRUCTURE OF ROOTS 35

the cortex consists of closely-fitting cells with thickenings on
their radial and outer walls. This layer is the endodermis
(Gr. endon = within). The inner tissues form the cen-
tral cylinder or stele, and consist of a layer of delicate
cells next to the endodermis, called the pericycle (Gr.
peri = around, kyklos = circle) ; within this are the veins
or vascular bundles, each being composed of three kinds of
tissue — an outer tissue, the bast or phloem (Fig. 15, b) (Gr.
phloios = bark) ; an inner tissue, the wood or xylem (w)
(Gr. xylon = wood) ; and between the two a very delicate,
actively growing tissue, the cambium (c).

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 young root. — The structure of a very young
root, however, is different (Fig. 15, 2). The bast is not
placed on the outside of the wood, i. e. collaterally, but the
two tissues are arranged in alternating groups, i. e. radially.
The groups of first-formed or primary wood (Fig. 15, 2, w,
and Fig. 16, r, 2, 3, p.w) develop from outside inwards (the
ends 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. It is not until a cambium ring
is formed, winding to the outside of the wood and to the
inside of the bast, that the arrangement found in an old
root is developed. Fig. 16, 1, 2, 3, makes this point clear.
Secondary 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. 16, 2, 3, s.w), and new bast to the outside
(Fig. 16, 2, 3, s.b) ; and in this way a ring of vascular bundles
is formed, each bundle consisting of the three tissues — ■
bast, cambium, and wood. At first the cambium is a wavy

c 2

THE VEGETATIVE ORGANS

line (Fig. 16, 3, c), but as growth proceeds it becomes a
uniform ring (Fig. 15, 1, c), to the inside of which is the wood
and to the outside the bast. The root has now lost its
radial structure and grows in thickness by additions from
the cambium in the same manner as in the stem. Finally,
a layer of cork is formed from a ring of cambium, the cork
cambium (Fig. 15, r, 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. 16. Diagrams illustrating the Development of a Root.
— 1, very young root, showing alternating groups of primary wood
(P.w) and primary bast (P.b) ; 2, older root, showing cambium (c),
arising on the outside of the wood and on the inside of the bast ;
3, old root, showing a complete cambium (c) ; co, cortex; e, epidermis;
s.w, secondary wood, formed on the inside of the cambium ; s.b,
secondary bast, formed on the outside of the cambium.

bundles and the cortex, and the latter dies and crumbles
away, as shown in Fig. 15, 1, co.

The loss 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 life.

Structure of a monocotyledonous root. — The root of a Mono-
cotyledon 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
the wood are to the outside, the later ones are well developed,
large, and in some species they meet and fill the centre of
the root with wood ; in others the middle is occupied by
a pith.

The tissues of the root are of several kinds and modified
to serve special purposes ; the root-hairs absorb from the
soil water which is passed through the cortex to the wood,
and the latter conducts it upwards to the shoots. The
organic food, which, as we shall see later, is formed in the
leaves, is 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 germinating seeds we found that the
root was the first organ to be formed, and that its appear-
ance was followed by the emergence of the young shoot.
What is the future of such a root ? How does it grow ?
Of what special use is it to the plant ? How does it do its
work ? A few experiments and observations will help us
to answer these questions.

Direction of growth of root and shoot. — In a pot of fibre
or soil, sow three soaked Bean seeds, one with the radicle
pointing downwards, another horizontally, and a third
upwards. After a few days examine them. In what
directions have the radicle and plumule grown in each ?
(Fig. 17, 1, 2, 3.) 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,

THE VEGETATIVE ORGANS

and that the plumule just as persistently grows upwards
into the air and sunlight.

The stimulus of gravity. Geotropism. — What force is at
work which determines these directions of growth ? If a
growing seedling is placed on its side and attached to a rod
which is caused to revolve horizontally by means of clock-
work (Fig. 18), the radicle and plumule will continue to grow
in that direction. An instrument constructed for the pur-
pose of rotating plants in various positions is called a

Fig. 17. Seeds of Broad Bean sown in Different Positions.
In each case the radicle grows downwards.

klinostat.1 Further, if seedlings of the Pea are pinned on
a 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 of
rotation, and the plumules turn inwards towards the centre.
In this experiment the seedlings have grown under the
influence of a force stronger than the attraction of gravity.
The influence of centrifugal force affects the radicle and

1 A simple form of klinostat may be made from a small clock
by removing the hands and fixing a short tube to the axle of the
minute-hand. Fit up a light bottle as a moist chamber and bore
a hole in the cork, into which the tube may be firmly fitted. Seed-
lings pinned to the cork may be rotated as in the experiment
described.

WORK OF THE ROOT

plumule in opposite ways. The radicle grows in the same
direction as that of the force, and the plumule grows in the
contrary direction. Such experiments establish the fact that
growing organs are sensitive to a physical force in nature,
and the force acting on plants in this manner is gravity, the
radicle growing along the line of action of gravity towards
the earth while the plumule grows in the opposite direction.
The response of growing organs to the attraction of

Fig. 18. Klinostat. — c, case containing a clock, by means of
which the glass cylinder (ra.c) is slowly revolved; in this are seed-
lings (p) growing on moist turf.

gravity is known as geotropism (Gr. ge = earth, tropos
= turning), the radicle being positively geotropic and the
plumule negatively geotropic. Any influence which acts
upon the living organs of a plant, and induces in them
a change of behaviour, is called a stimulus. In addition
to gravity, plant organs respond to many other stimuli,
e. g. light, heat, contact, electrical currents, also to water
and other chemical substances. These stimuli are impor-
tant factors in the environment of a plant, and as they vary
frequently, it is necessary for the plant to respond and

4o THE VEGETATIVE ORGANS

adjust itself to the changing conditions. The power of
response and adjustment is the most characteristic feature
of life, and it is important that we should pursue the
subject a little 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-filled with stones or frag-
ments of broken plant pots, moistened with a little water.
Then attach two or three seedlings to the cork, and suspend
them with the radicles directed downwards into the bottle.
Notice what happens as they come into contact with the
hard fragments. The roots turn away, escaping the injury
which would result if the tip were forced against a solid
object.

The sensory region of the root. — This shows that some part
of the root must be sensitive, and the following experiments
determine the sensory region of the root.

Take four seedlings of the Broad Bean [a to d) with
radicles about i\ inches long, and treat them as follows :

i. Place seedling a horizontally on moist coco-nut fibre.

2. Take a razor and cut off one-sixteenth of an inch from
the tip of the radicle of seedling b and place it alongside a,

3. Place seedling c, uninjured, on its side for an hour,
then cut off the tip as in b and lay it horizontally on the
moist fibre.

4. Place seedling d on its side for a day until its tip has
curved downwards, then cut off the tip as with b and c,
but place the seedling with the root pointing downwards.

Allow the seedlings to grow and carefully compare the
results.

a turns downwards ; b grows, but does not bend ; c bends
as in a ; d does not turn downwards, but continues to grow
horizontally.

If the seedlings are allowed to grow under favourable

WORK OF THE ROOT

conditions a new tip is formed and grows downwards as
in an uninjured root. We thus see that, though able to
grow 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 region of the root.
The stimulus of water. Hydrotropism. — To pursue the
subject of root sensitiveness further, perform the following
experiment. Obtain a shallow box, remove the bottom,
and replace it by wire gauze (Fig. 19). Fill the box with
wet coco-nut fibre and sow in it a number of peas. Tilt

Fig. 19. Experiment to show that Roots are sensitive
to the Stimulus of Water.

the box at an angle of 450 and protect the bottom from
strong light. As the seeds germinate, the roots, owing to
the 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 back
and grow upwards into the wet fibre. From previous
experiments we should expect the roots to grow vertically
downwards in response to the stimulus of gravity. What
other force is now operating to draw the roots away from
the vertical direction ? We see that the attraction of water
is, under these circumstances, more powerful than that of
gravity. This tendency of roots to turn towards or be

42 THE VEGETATIVE ORGANS

attracted by water is called hydrotropism (Gr. hydor
= water). Roots are attracted to, and grow best in, the
moist layers of the soil ; and the roots of trees and shrubs
may be drawn considerable distances in the direction of
a suitable water-supply. A dry soil retards root growth.

In this connexion it 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, is concentrated on that part of the ground
immediately round the stem. Such plants have commonly
a long tap-root but no wide-spreading root-branches. In
other cases the leaves are so arranged as to throw the water
from their tips and the water falls over a larger circle to
the outside of the plant. The watershed of such a plant
is therefore a large one, and on examining its root-system
we find that the young absorbing branches spread exten-
sively, and collect water from a corresponding area.

The stimulus of light. Heliotropism. — If we observe the
roots of the Ivy we shall find that they very generally
turn 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 it is equally true that
they are growing towards the shady side and away from
the light. That roots can be tempted to grow from the
usually exposed surface of the Ivy stem can be shown by
the simple experiment of keeping a portion covered with
a wet cloth ; the roots will soon be seen to grow under
the cloth.

Suppose, however, that seedlings are grown on gauze
over a jar of water so that the roots hang downwards
into the water. If we now exclude light from the jar at
every point except a narrow slit on one side, through
which a strong light can be admitted, the growing roots

WORK OF THE ROOT

will turn away from the light towards the shaded
side. Thus Ivy roots are probably not merely growing
towards the moist surface, but also away from the sun-
light. The sensitiveness of growing organs to sunlight
is termed heliotropism (Gr. helios = sun), but as roots
usually turn away from, and not towards, the light
they are said to be negatively
heliotropic.

Our experiments have shown
that roots are sensitive to a
number of different stimuli,
namely, gravity, contact, water,
and light, and that in response
to these stimuli roots grow in
a definite manner. We will now
determine the important fact
that roots are sensitive only in
the presence of oxygen.

Necessity for oxygen. — Take
a wide-mouthed bottle fitted
with a good cork or stopper,
and fill half of it with water that
has been boiled so as to expel
the dissolved air. Select two
seedlings of the Pea with radicles
about an inch long. Take a board
(which has been previously boiled
to destroy mould-spores) and pin the seedlings to it in
such a way that the radicles are directed horizontally
as in Fig. 20. Place them in the bottle, submerging
one in the water (a), and placing the other well above
the water in the air (b) ; then close the bottle with
a stopper. Ensure that both seedlings have their radicles
directed downwards and place them horizontally only
when putting them into the bottle. Leave them for

Fig. 20. Experiment to
show that the root is
not sensitive in the ab-
SENCE of Oxygen. — a,
seedling in boiled water ;
b, seedling in air.

44 THE VEGETATIVE ORGANS

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 it
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 of growth ?

Respiration. — A simple experiment will enable us to
understand the important role played by plants in changing
the composition of the air. Soak a number of peas in
water for a day, and then place them in two jars (a and b)
lined with wet blotting-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 jars as follows : (a) insert a lighted taper,
and note whether the air in the jar containing the peas
will now support combustion ; (b) pour in a little lime-
water and note the result. From these tests we see that
the 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. If we breathe on to lime-water we observe a
similar effect. In other words, Peas, during their growth,
are using up oxygen and giving off carbon dioxide, just as
we are when breathing. This process, which is called respira-
tion, is necessary to the existence of plants ; they would soon
die if kept wet in a closed bottle and without air.

The oxygen taken into the tissues of the plant during
respiration acts chemically upon the complex organic sub-
stances which constitute the plant, with the result that
they are converted into simpler compounds such as carbon
dioxide and water. During these changes energy is set
free, and thus the work necessary to the life of the plant

WORK OF THE ROOT

is performed. Some of this energy appears as heat which
helps to maintain a suitable temperature within the living
tissues of the plant.

In describing the Stock we spoke of the growing-points
of root and stem. The root in pushing its way through the
soil meets with much resistance, but is protected at the
tip by a root-cap, the end of which is constantly dying
and wearing away, to be re-
placed by new tissue. On the
other hand, the stem-tip has no
cap, but is protected by the
overlapping leaves which form
the end bud.

Growing-region of the root. — It
will be interesting to compare
the manner of growth of root
and stem and to determine
experimentally the mode of
elongation in each case.

Select a germinating Bean
with a radicle about an inch
long, wipe off adhering par-
ticles, taking care not to injure
the Bean in any way, and
mark about a dozen lines across
it in Indian ink. This can be

done as follows: Take a piece of cotton thread and
hold it by both ends ; bend it, and dip the middle of
the thread into the ink. Then lay it across the root
so as to make a clear transverse mark. Begin quite
at the tip and make a series of marks about ■£* inch
apart backwards from the tip. Obtain a large, wide-
mouthed bottle or jar fitted with a cork (Fig. 21).
Line it with blotting paper so that the lower edge dips
into about half an inch of water ; this provides a moist

Fig. 21. Bean Seedling
marked to determine the
Region of Elongation in
the Root. — 1, at the com-
mencement of the experi-
ment; 2, at the end of 3o|
hours.

46 THE VEGETATIVE ORGANS

chamber in which to grow the seedling. Push a large pin
through the cork and fix the Bean seed firmly to the point ;
then replace the cork in such a way that the marked
radicle hangs downwards within the bottle so as to avoid
touching the sides. Make a sketch of the radicle at the
commencement of the experiment, showing the exact
number of lines and their distance apart, and at the end
of two or three days make another sketch and note what
has happened (Fig. 21, 2). Has the root grown ? Count the
lines and compare them with the original sketch. What
is their position now ? Which lines are most widely
separated ? What changes have occurred in some of the
lines ? Has elongation occurred at the extreme tip, or is
the position of the first line still unchanged ? We observe
that the extreme tip (the end of the root-cap) has not
grown, but that elongation has been most active in the
region immediately behind this and included within the
next two or three lines, which, as the root has elongated,
have been drawn out and now appear as a number of
dots.

Region of curvature. — Mark the radicle of another Bean
seedling and place it in a moist chamber as before, but
fix it with the radicle horizontal. Allow it to grow, and
note where curvature takes place. Observe that the regions
of curvature and elongation coincide and are included
within 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
allow 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

WORK OF THE ROOT

injured and its growth stopped, look for roots emerging
from the base of the stem. In a still older plant, note
what a large part of the soil is drained by the later branches
which grow in various directions.

Growing-region of the stem. — On seedlings still growing
in the pots carry out a similar experiment with the stem,
selecting plants in which the plumule has emerged an inch

" 2 ~ 3 *

Fig. 22. Mode of Emergence of the Cotyledons of
Sunflower Seedlings. — 2, 3, and 4 show the region of
elongation {a-b) in the hypocotyl.

or more above the soil. Beginning at the tip, make a series
of lines backwards as far as convenient. Make a sketch
true to scale and show in it the exact number of lines
(Fig. 22, 2). Seedlings of Sunflower and Kidney-Bean
(Fig. 10) serve well for this experiment. Allow them to
grow for a few days and note the result (Fig. 22, 3 and 4).
We see that the region of growth in a stem {a-b) is not
confined to such a small area as it is in a root.

48 THE VEGETATIVE ORGANS

Absorption by Roots

Root-hairs the organs of absorption. — If young roots,
bearing root-hairs, are examined by means of a pocket lens
or under a microscope, it will be seen that each root -hair
consists of a long, tubular outgrowth of an epidermal cell
(see Fig. n, 7, e). The wall (c.w) consists of a thin mem-
brane of cellulose, the substance of which the fibres of
cotton are composed. The outer exposed surface is some-
what slimy, and to this the soil-particles adhere firmly.
Within the tube is the living substance known as proto-
plasm (p), together with a little rounded body — the nucleus
(n). The protoplasm forms a thin living lining to the tube ;
and 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 surface
tissues are corky and no root-hairs are found. Root-hairs
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 in
a plant which a gardener would describe as ' pot-bound ',
i. e. a plant which has grown so long in a pot that its roots
have spread themselves out in a tangled mat between the
soil 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 soil
are tough, wiry, and covered with a firm brown layer of
cork.

What are the uses of these different parts ? The root-
cap doubtless serves to protect the young growing root as
it pushes its way through the soil. The older parts, sur-
rounded 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 polished marble,
place it in the bottom of a shallow box, and cover it 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 it. The tracks of the roots are
clearly marked by the corrosion of the polished surface.
Now take a little dilute hydrochloric acid, dip into it
a small camel-hair brush, and write the date of the experi-
ment on the polished surface. When this is dry it will 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 similarly leave its trail. Can it be that the young
roots and their root-hairs during their 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 mineral
substances in the soil. Thus they may bring into solution
substances otherwise difficult to dissolve, and these may
be absorbed as food by the plant.

Wilting. — Allow a plant growing in a flower-pot to
remain un watered 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 how
soon the leaves droop. Place the cut end in water, cut
off a small piece (under water), and note how quickly the
shoot revives. We see that, as the soil loses water, the

159B D

THE VEGETATIVE ORGANS

shoots above ground droop or ' wilt ' , but on renewing the
water-supply they become turgid, i. e. the tissues absorb
water. The leaves expand and once more become firm.
Water is essential to enable a plant to maintain its firmness.

Fig. 23. Osmosis Experiment.
a, thistle funnel containing sugar solution ; b, jar of water.

Osmosis

Osmosis is a natural process which has an important
bearing on the work of roots. We shall best understand
it by means of the following experiment. Obtain a thistle
funnel and with a piece of moistened parchment paper
close the mouth of it as in Fig. 23. Tie the paper firmly
round 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 51

At definite periods of time mark the height of the rising
column by means of narrow strips of gummed paper. If
the solution is sufficiently strong, the liquid will rise con-
siderably, 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 connecting a long piece of glass
tubing to the funnel by means of a piece of rubber tubing.

Consider the conditions of the experiment. In the bulb
of the funnel is a dense solution separated from a weak
solution 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 solution, whilst, 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 liquids of different densities through a per-
meable membrane which originally separated them is called
osmosis.

Let us now compare the conditions of the roots in the
soil with those of their counterpart in this experiment.
The root-hairs may be regarded as corresponding to the
closed funnels, their contents a dense solution, and their
walls permeable membranes. The soil-water will now be
the weak solution separated from the dense solution within
the root-hair by (1) the outer slimy or mucilaginous layer
which readily absorbs the soil-water, (2) the permeable
cellulose 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 sub-
stances shall enter or leave the cell. From such a com-
parison we are able to obtain some idea as to how water
is taken up by the root-hairs and passed on to the inner
tissues of the plant. The process, however, is extremely
complicated, partly owing to the complex nature of the

D 2

52 THE VEGETATIVE ORCxANS

cell-contents and the selective power of the plasmatic
membranes.

Each of the fine particles of which the soil is composed
is coated with a thin film of water containing mineral salts
in solution. The root-hairs press against and become
moulded to the particles, and water (together with a selec-
tion of the dissolved mineral salts) is drawn into the root-
hair. This continues as long as the osmotic attraction of
the cell-contents can overcome the surface tension of the
film of water surrounding the soil-particle. If water is
renewed from adjacent particles absorption will continue:
if 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.

Turgidity. — 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 have
seen how very small and tender the root-hairs are and how
easily injured, and we have noticed also their great impor-
tance as absorbing organs. The movement of the soil in
digging up and transplanting will obviously break off a large
number of these hairs and so reduce the absorbing power
of the root, hence wilting will occur. New root-hairs,
however, are gradually formed, which absorb water and
soon bring the plant back again to its fresh condition.
The condition of living cells, whereby their elastic walls
are stretched by the pressure of internal fluids, is called
turgidity. The freshness of a shoot depends upon its
turgidity ; loss of turgidity is the cause of wilting.

Potato osmometer. — Another experiment will enable us
to realize how the water taken up by the root-hairs may
travel through the outer to the inner tissues of the root.
Obtain two long and similar potatoes with uninjured skins.
Boil one of these for fifteen minutes and allow it 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 each
potato 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. Place
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 f^S~^S\

sugar solution has withdrawn water / \ a

from the cells lining the cavity, the I 4 \

sap of these cells thereby becoming I L

concentrated. These cells now with- p^~^^^^l b
draw water from those farther lc^__ _--<£>

outwards ; and this is repeated „

.. , „ c . , , Fig. 24. Potato

until the cells of the pared surface osmometer.-*, cavity

outside, which draw water from the in potato containing

dish, are reached. Very different is sugar ; b, dish of 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 level of the liquid in the two cavities. In the

living potato the liquid rises in the tube and eventually

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

will help us to realize the activity of living tissues in

taking up and transmitting water, as compared with the

action of a dead tissue.

We are now in a position to understand the importance

of root-hairs to a plant. The root-hair region, together

with the younger part of the root which has not yet formed

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

54 THE VEGETATIVE ORGANS

The root-hairs are often of considerable length, and their
form and number very greatly affect the absorbing power
of a plant, e. g. the root-hairs of Maize increase the surface
of the root five and a half times ; while those of Barley
increase the surface twelve times. In some plants with
very 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 depend
for their supply of water and mineral food on the absorbing
activity of the root-hair region.

The Food absorbed by a Root

Soil-organisms and their work. — Ordinarily the soil in
which the roots of plants grow is a very complex mixture
of substances — solid, liquid, and gaseous ; inorganic and
organic ; living and dead ; animal and vegetable. Myriads
of tiny organisms find a home there, and also bigger ones
such as earthworms and the larvae of many insects. These
feed upon the living and dead materials in the soil, reducing
them 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 the
food of a green plant. The organisms, however, differ
much in their usefulness in this respect ; earthworms are
great ploughers and pulverizers of the soil, and minute
organisms, like bacteria, are valuable or even indispensable ;
but others prey upon them and, by reducing their numbers
and therefore their usefulness, retard the formation of
soluble food-materials, thus rendering more and more
difficult the sustenance of plants. But these foes in turn
are checked by others, and so this complex society of inter-
dependent and ever-changing members is actively at work
reducing the complex materials and preparing from them

WORK OF THE ROOT

suitable food for succeeding generations. It is important,
however, that a suitable balance should be maintained
between the organisms in the soil, if higher plants are to
thrive in it. From what we have seen, the food which an
ordinary green plant can take up from the soil must be
a weak solution of inorganic substances, e. g. compounds
which form the mineral matter of the soil as distinct from
organic substances which are carbon compounds built up
by living organisms, e. g. cellulose, sugar, starch, and
proteins.

Water -cultures. — If soil-water or ordinary tap-water be
placed in a shallow vessel and covered by a sheet of paper
so as to prevent access of dust or other matter, and allowed
to evaporate, a sediment will be left at the bottom of the
vessel, consisting of substances which were held in solution.
These, when analysed, are found to consist of a number of
mineral salts which, in suitable proportions, are able to
sustain a green plant grown under the usual conditions
of air and light. Such a sediment, however, may possibly
contain substances not necessary to the plant.

Experiments have been made to determine which of
these compounds are essential. The following solution con-
tains the inorganic substances commonly present in a
natural soil : —

Distilled water (HO)

Potassium nitrate (KNOJ
Sodium chloride (NaCl)
Calcium sulphate (CaS04)
Magnesium sulphate (MgSOJ
Calcium phosphate (Ca.,(P04) )
Ferric chloride (FeCl3)

Such a solution is known as a normal water-culture solu-
tion, and in it plants may be grown up to the flowering and
fruiting stages (Fig. 25, b).

1,000 c.c.

i-o grm

o-5 „

0-5 „

05 ,,

a trace.

THE VEGETATIVE ORGANS

Fig. 25. Water-cultures of Buckwheat (Pfeffer).

a, without potassium ; b, normal solution ; c, without iron ; d, cover

split to receive the plant stem ; g, jar containing culture solution.

WORK OF THE ROOT 57

In order to show the importance of the various con-
stituents, plants should be grown in the following incom-
plete culture solutions and the results compared : (1) Cul-
ture solution without potassium nitrate (Fig. 25, a), (2)
without magnesium sulphate, (3) without calcium phos-
phate, and (4) without ferric chloride (Fig 25, c).

It will be interesting to carry out such experiments, but
as the results are often very variable and contradictory, it
is well to try several of each and express the average results
by means of curves. The jars containing the food solu-
tions should be covered with opaque paper in order to
exclude light, and the solutions 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 stem 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-culture experiments
prove to be non-essential. Silica, which is present in large
quantities in Grasses, Horsetails, &c, is one of these.
Chlorine also is necessary to only a very few species. On
the other hand, if potassium compounds or nitrates are
omitted, the plant suffers. If iron is omitted, chlorophyll
is not developed, and the leaves are sickly yellow in colour
(Fig. 25, c). By means of water-culture experiments we
learn that the food of a green plant must contain the
following elements : oxygen, hydrogen, nitrogen, calcium,
magnesium, potassium, phosphorus, sulphur, and iron ; all
of which a plant obtains in solution from the soil. One
important element, carbon, forms about half the dry weight
of a plant, yet is not present in a culture solution, nor is the
plant able to obtain it from the soil. The question there-
fore arises — How does a plant obtain the carbon which

58 THE VEGETATIVE ORGANS

forms so large a proportion of its substance ? But this
is a question we cannot answer until we come to the work
of leaves.

From the above observations we learn that in many
plants 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 is replaced by
adventitious roots from the stem. Roots fix the plant in
the soil and absorb weak solutions of mineral salts ; the
absorbing 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 are
not 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 cells
of the pericycle and opposite the groups of primary wood,
branch roots arise in vertical rows. The tip of each root
is protected by a root-cap and possesses a sensory region
which is able to perceive a stimulus and transmit an impulse
to the neighbouring tissue, where growth occurs. The root
is sensitive only in the presence of oxygen. The direction
of growth is determined by the nature of the stimulus,
i.e. towards the soil, water, and food; and away from
obstacles and light. Some roots, swollen with a large
cellular tissue, 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 Dicotyledons (e. g. Bean, Pea, and
Stock) the radicle 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

numerous branching fibres. In Wheat, Oat, Maize, roots
are developed not as branches of the radicle, but from the
stem. The radicle is usually short-lived, and the roots are
all similar and slender, and known as fibrous roots (Fig. 26,
4). As they are developed from some part of the plant

Fig. 26. Abnormal Forms of Roots. — 1, conical
root of Carrot; 2, spindle-shaped root of Radish; 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 its branches, they are known as
adventitious roots, and in Monocotyledons they are the most
common kind.

Storage, climbing, and aquatic roots. — In exceptional
cases (Fig. 26, 1-3) roots thicken considerably. The tap-
root becomes conical in the Carrot and Beet, and spindle-
shaped and sometimes globular in the Radish. The Lesser

6o THE VEGETATIVE ORGANS

Celandine (Fig. 28) and Dahlia have swollen or tuberous
roots. Such swollen roots serve as important food-stores
for the plant, and some of them, if tested with iodine solu-
tion, will be found to contain much starch. Others, like
Beet, contain cane sugar, and the Dahlia contains an allied
substance called inulin. Frequently plants produce roots of
more than one kind and serving different functions, (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. 84), Bluebell (Fig. 87). The adventitious roots of the
Ivy, which arise in clusters on the aerial stems, serve rather
as holdfasts and climbing organs than for the purpose of
absorption. The roots of some water-plants like the Duck-
weed (Lemna) (Fig. 26, 5) and Frog-bit (Hydrocharis) dangle
in 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 serve
as floats.

Aerial roots. — Roots, though rarely green, do sometimes
develop the green colour characteristic 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 :

(1) 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 collects
on the bracket of leaves.

Adventitious shoots : suckers. — One of the most constant
characteristics of roots is that they give rise to members
similar to themselves, viz. root-branches. Thus they differ
'from stems, which produce members unlike themselves,
viz. leaves, which are usually green. It often happens,

FORMS OF ROOTS

however, that roots give rise to leafy shoots. Familiar
examples are Dock and Dandelion. If, in attempting to
eradicate these from a lawn, we cut the plants so as to leave

Fig. 27. Plant of Raspberry, bearing a sucker (s)
on its root (r).

part of the tap-root in the ground, leafy shoots eventually
spring from the buried portion of the root. In the case
of the Dandelion, often five or six shoots, each bearing a
rosette of leaves, will appear in the place of the part we

62 THE VEGETATIVE ORGANS

have removed. Such shoots are called adventitious shoots.
Some shrubs and trees often produce adventitious shoots
from horizontal root-branches, e.g. Raspberry (Fig. 27),
Rose, Bramble, Hawthorn, Poplar, and Hazel. Shoots
arising in this manner from roots are called suckers.

Roots vary greatly in their duration : they may be
annual, a fresh crop being produced each season ; biennial,
living two years only ; or perennial, living for many years.
Even among perennials, some roots, such as those of bulbs
and corms, often live only one season ; the bulb of one
season dying away and leaving an offshoot or bud to con-
tinue growth which forms roots of its own.

Tuberous roots of Lesser Celandine.— -The Lesser Celan-
dine has roots which show some specially interesting
features. The plant flowers in the early spring. Some-
times it grows in open, sunny places and receives frequent
visits 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
studied. We have already seen (p. 60) that this plant
produces two kinds of roots (Fig. 28). From what part of
the plant do the tubers spring ? How do they grow ? How
is the compact cluster of tubers formed ? Of what uses are
the tubers to the plant ?

Take a few seedlings (Fig. 28, 2, 3, 4) and note the coloured
scale (sc) at the base and the small green foliage-leaf. In
the axil of the scale a tuber (t) is formed, which bursts
through it and grows parallel to the root (r). Later, a
young shoot elongates, uses up the food- reserves in the
tuber, and forms one or more leaves (I) . In the axils of these
leaves new tubers develop, and may often be found to elon-
gate and turn sharply over the edge of the sheathing-base
on their 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,

FORMS OF ROOTS

you will find the cortex to be very large, the cells crowded
with starch grains, and the central cylinder, a small strand
in the middle, to contain four groups of wood alternating
with four groups of bast.

If a shoot, bearing axillary tubers, be placed in water for

Fig. 28. Development of Tubers in the Lessek
Celandine. — i, plant with tubers at successive nodes;
2, 3, 4, seedlings bearing axillary tubers ; 5, tuber
bursting through the leaf -sheath; 6, node with axillary
tubers, one bearing a leaf ; 7, ditto, with the two leaves
removed ; /, fruit ; I, foliage-leaf ; /, tuber ; r, root ;
sc, scale-leaf.

a few days, leaves may be seen to arise from the axils of
scale-leaves at the bases of the tubers (Fig. 28, 6 and 7).
Tubers, therefore, are compound structures : the lower leaf-
bearing portion is a stem ; and the outer or distal part is
a root with a double function : (a) it absorbs by means of
root-hairs, and (b) stores up starch in the bulky cortex.

64 THE VEGETATIVE ORGANS

Such axillary tubers occur commonly on the older plants ;
and, as the other parts decay, the tubers fall to the ground,
and in time produce new plants from the buds which arise
at their base. Two or three tubers may arise at a node,
and when several leaves are produced close together a large
cluster of tubers results.

Fig. 28, 1, shows tubers springing from three successive
nodes. By the elongation of the tubers they may enter
the soil and become independently rooted. The decay of
the 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 vegetative
means, is of common occurrence.

CHAPTER VI
STRUCTURE OF THE SHOOT

Environment of the root and shoot. — The environment of
the shoot is totally different from that of the root. In the
soil the root is surrounded by a moist medium, and is in
the dark. It is less exposed than the shoot to drying winds
or heavy rain, to biting cold or the bright rays of the 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 often
extreme changes as are those parts growing above ground.
For healthy existence, their form and structure must be
adapted, not only to withstand, but to make the best use
of, these conditions. We have, therefore, to regard the
shoot of a plant from these different 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 air.
It is obvious, too, that the stem is the means of communica-
tion between root and leaf. In order to bear the weight of
leaves and branches, and to withstand the strain of heavy
winds, it needs to be strong ; and to resist the attacks of
numerous enemies, its outer surface must be tough or
otherwise resistant. To prevent the escape of sap, which
passes along the stem, it must be impervious. Structures
thus exposed to many and varied conditions, and having
to serve so many purposes, are likely to show a wide range
in duration and modification of form and structure.

Though the leaf and stem differ in many details from the
root, they are built up of the same general tissues — an
epidermis on the outside enclosing a cortex, and, within,
a ring of vascular bundles surrounding the central pith.
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.

Structure of the Box leaf. — A simple dissection will show
the relationship of these different, tissues of which the leaf
is composed. Boil a few Box leaves in a solution of caustic
potash for fifteen to twenty minutes, then wash gently in
water, 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, 1 and 2). There now remains the
skeleton, the meshes of which are covered by and filled in
with a soft green tissue. With a camel-hair brush carefully
remove this tissue, and so prepare a clean skeleton (Fig. 30).
Examine all these parts carefully with a pocket lens. How
do these skins differ ? Is one more readily removed than the
other ? and if so, which ? What structures do you find on the
under skin which are absent from the upper one ? Examine
these with a microscope ; and also the green tissue you have
removed from the meshes of the veins. Each of the dots,
seen with a lens on the under skin consists of two sausage--

1200. 5.

THE VEGETATIVE ORGANS

shaped cells joined end to end, leaving a pore or mouth
between them (Fig. 29, 1 and 4 s). These openings are
called stomata (sing., stoma, Gr. stoma = the mouth), and
their function is to communicate between the interior of
the leaf and the air outside. On the upper skin (Fig. 29, 2),
however, these are almost or entirely absent.

Fig. 29. Structure of a Box Leaf. — i, part of lower epidermis ;
2, part of upper epidermis ; 3, cross-section of Box leaf ; 4, part
of 3 at the point u, I, highly magnified ; 5, a cell of the mesophyll ;
a, air-chamber; b, bast; c, cuticle of epidermis; ch, chloroplast ;
g, guard cells ; I, lower surface ; l.e, lower epidermis ; n, nucleus ;
P, protoplasm ; P.t, palisade tissue; s, stoma ; sp, spongy tissue ;
u, 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 skins
is seen to be arranged in two distinct layers ; the upper
one, called the palisade tissue, consists of perpendicular
elongated cells, closely packed together and attached above
to the upper skin (Fig. 2g,4p.t). The cells below, known
as the spongy tissue, are loosely arranged, leaving large

STRUCTURE OF THE SHOOT

spaces between them filled with air (Fig. 29, 4 sp). These
cells 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. chloros= green, pIiyllon = 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 the meshwork of veins (Fig. 30) .
We can understand from such a section why the lower skin
should be more easily removed than the upper.

Structure of the stem. — Turning now to the tissues of a
stem like the Buttercup (Fig. 31), Dead-
nettle (Fig. 34), or Bean, we find these
similar to and continuous in structure with
those of the root and leaf ; and they are
also similar in function. A layer of cells—
the epidermis (Fig. 31, e) — covers the outer
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 the
epidermis is the cortex (co), followed by a
ring of veins, or vascular bundles (v.b). In
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 pith — occur generally
in plant stems, but become greatly modified according
to the requirements of the plant.

The epidermis may develop a very thick cuticle in ever-
greens, and is usually waxy and more or less impervious.
In water-plants the cuticle is often very thin or absent.
In some plants, hairs are so abundant as to produce a woolly
covering. Not uncommonly some hairs pour out a sticky

Fig. 30.

Skeleton of

Box Leaf.

k 2

68 THE VEGETATIVE ORGANS

secretion, e. g. Campion and Catchfly ; while in other
plants they secrete a poisonous acid and the hairs become
formidable stings, e. g. Nettle.

The cortex and mechanical supporting tissues. — Beneath
the epidermis is the cortex, and the cells of the outer part,
especially in herbaceous stems, may be strongly thickened
so as to form a firm supporting tube (Fig. 36 scl). In the
Deadnettle, the cortical cells of the angles of the stem are
strongly thickened at their corners (Fig. 34), and these,
together with the wood of the large bundles, are effective in
protecting the stem against the stresses of tension and com-
pression ; in fact the whole stem is built on the principle
of a box girder. A tissue consisting of cells which retain
their living contents, and whose walls are thickened at the
corners, is called collenchyma(Gr.fo//g« = gelatinous matter,
chyma = an infusion). A ring of collenchyma occurs in
the outer cortex of the Sunflower stem (Fig. 37), and it
is frequently found in leaf-stalks. Bands of cells in the
cortex of the Bracken and Birthwort are uniformly thickened
and devoid of living contents. Those of the Birthwort
(Fig. 36) form a strengthening ring immediately beneath
the epidermis (sc1), and a second one (sc2) as a strengthen-
ing cylinder midway between the epidermis and the bast.
Such a mechanical supporting tissue is called sclerenchyma
(Gr. skleros = hard).

The ring of wood in the Elder (Fig. 38, w) forms a sup-
porting mechanism on the principle of a hollow pillar, while
in older woody stems the arrangement is that of a solid
pillar. 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.

Structure and arrangement of vascular bundles. — A com-
parison of Figs. 31 to 34 and 36 to 39, which are transverse

"— j

• •*

ccj

E
o
o

J3
o

1-1
Q

<J"

-t->

■■>

"«*i

4->

■ -

+->

CD
'cn

t3
O

1— I

t— 1

-C

►sT

i-<

CD
—

«T

Co*

. ^

M
C/5

— <

■^

. _

>-.

!-l

l-i

M
CO

cd"

-3
a

i-i

CtJ

-
-

-i->

C/J

C/)

C/3

l-i

(/)

bX)

u-}

1— 1

(3
|3

— H

■»

O
tn

•-

►o

'ft

„

1— i

,£3

• ■*

C/3

■ —

S-i

tfl

0->

-r
o
*d

„

•d

■3

1-1

C/3

l-H

0
bo

C/3

t/J

c/3

■■»

—

X c/3

■i

ffl

• -

<-•

C/3

d
o

1/3

-t->

3
O

z
<

__-

—

• •*

+-»

(/)

+■>

STRUCTURE OF THE SHOOT 69

sections through the internodes of several dicotyledonous
stems, shows that the vascular bundles are arranged in the
form of a ring. Fig. 32 shows one of the vascular bundles
of the Buttercup, highly magnified. Note the three dis-
tinct groups of tissue of which it is composed. On the
outside is a group of delicate cells, the bast or phloem (b) ;
the larger elements — sieve tubes (s) — are accompanied by
very small ones, called companion cells (c) ; both are hlled
with organic materials. On the inner side of the bast is
a band of narrow, flattened cells — the cambium (ca). In
that portion adjoining the pith is the wood or xylem (w),
composed of wide, tubular, thick-walled 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 parallel course which a section through
the internode might suggest. Numerous examples of this
may be obtained from waste heaps where shoots such as
old cabbage-stalks are undergoing decay.

With a little 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 stems may be boiled in water to which a little
caustic potash has been added. This softens the cortical
tissues so that they may be brushed away from the veins,
as was done in preparing the skeleton of the Box leaf. If
a piece of stem including two or three pairs 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 join on to neighbouring veins. This will be clear
from a study of Fig. 33. By means of these veins direct
communication is set up between roots, stem, and leaves.

Fig. 34 shows the arrangement of these tissues in a trans-
verse section of the Deadnettle stem. At the corners are
the large fused bundles from the leaves (v.b), while at the
sides are the small bundles. In this stem the innermost

7o THE VEGETATIVE ORGANS

layer of the cortex stands out clearly as a layer of larger
cells— the endodermis {en). Examine the mature stem of
the Bean and compare it with that of the Deadnettle.
Although these stems are square, the general arrangement
of the tissues is the same as that which is found in the

Buttercup.

Scattered bundles of Monocotyledons. — The stems of

Monocotyledons differ in several
important respects from those just
described ; the vascular bundles are
scattered in the ground tissue (Fig.
35), and there is no cambium be-
tween the wood and bast, so that
when once these bundles are formed,
no further increase in thickness is
possible in them. They are therefore
called ' closed ' bundles to distin-
guish them from the ' open ' bundles
of Dicotyledons which possess a
cambium.

Woody stems. Secondary growth. —
The cambium of Dicotyledons,
though a small and inconspicuous
tissue, is a very important one, in-
asmuch as its cells are able to divide
repeatedly and form new tissue.
That formed on its outer side be-
comes part of the bast, while that
formed on its inner side adds to, and
increases the thickness 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 cam-
bium ring (Fig. 36, i.f.c) . This later-formed cambium, called
interfascicular cambium, produces small new bundles
between the original large ones, as shown in Fig. 37. Growth

Fig. 33. Diagram
showing the arrange-
MENT of Veins in
a Deadnettle Stem
(after Farmer).

STRUCTURE OF THE SHOOT 71

continues, bundles are introduced, and ultimately a compact
ring of wood is formed with thin medullary rays between
the bundles (Fig. 38) .

The formation of new tissue and especially of woody
tissue goes on actively in the spring and summer ; less is
formed in the autumn ; and little 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 with
each other, and may be clearly seen in a transverse section.
These annual rings (Fig. 39, a) are often irregular, and some-
times more than one ring may be formed in a season, but
their 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, unlike animals, they may add
to their body-substance year by year.

These different tissues may be determined by dissecting
a piece of Elder stem. Outside is the thin dying epidermis
with a layer of cork below ; next the green cortex, followed
by the slimy tissues of bast and cambium. The firm wood
is easily discovered surrounding the central pith. 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 its name.

Cork
Cork and lenticels. — During the early stages in the de-
velopment of the woody tissue of Dicotyledons, the outer
cells of the cortex and epidermis keep pace with it, but
eventually they lose their power of increasing and tend to
give way under the internal strain. Meanwhile, provision

72 THE VEGETATIVE ORGANS

is being made for a new protective covering. There arises
in the cortex another kind of cambium, known as the cork-
cambium, because its cells by repeated division form, not
wood and bast, but cork. Fig. 38 shows this cork-cambium
(c.c) arising just below the epidermis (e) in the stem of the
Elder, and its cells have divided in such a way as to form
somewhat regular rows of cells. These enlarge, lose their
living contents, and their walls become transformed into
cork (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 from
year 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
irregular group of cork cells is formed beneath a stoma, the
cells being so arranged as to permit air to enter or leave the
stem. These structures, which take the place of stomata,
are called lenticels (Fig. 42, /) and are formed on most
trees, their shape being peculiar to the species.

Other stems should be examined and compared. In the
Laburnum the cork-cambium is formed in the middle of the
cortex, while in the Black Currant it arises deeper still,
near the ring of vascular bundles (Fig. 40 c.c). As the cork
develops, the cortex to the outside of it dies and is eventually
thrown off.

Callus and separation-layer. — The formation of 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 place
around the cut surface of a branch. You will be able to
lind all stages of cork-formation from a narrow ring just
outside the wood to others broader and broader, gradually
encroaching and growing over the surface of the wound

<="

• *

C/J

H
O

w
in

T3
O

4->

,£>

t/1

'fl

1-1

cf\

. „

-4->
l-i

►J

-&:"

-d

—

■ —

£1

(7)

o
o

„

—

C/3

• *

<A
W

1-1

l-t

-r

'a,

<4>"

<«r

. r.

+->

,fl

i-i

►>*

4-J

I-.

f*^

H
(J

■+■>

-4-"
CO

+■>

— <

I-.

<4H

o •

°^

1 #*

*ft

'-»•.

—

In
O

l-H

l-l

_aj

<cT

H
U

K
W

ni
o

>
co

Z
<;

+->

-r
ft

-a

rfS

«H

4->

•*

u
<!

c 3

STRUCTURE OF THE SHOOT

and eventually closing it up. Such a healing tissue of cork
is called callus.

An interesting case occurs in leaves. Examine shoots of
Privet, Ash, or other common shrubs or trees in the summer,
and look carefuUy at the leaf -bases ; bend the leaf back-
wards, and note where it tends to break. Here a distinct
ring is clearly seen (Fig. 42, s. I), and as the leaves grow older,
they break off along this line very easily.
Observe what happens later in the season
and examine shoots just before the leaves
begin to fall. By means of a lens a
healing scar of cork may easily be seen
stretching like a plate across the leaf-
base. Note how easily the leaf breaks
off here, and also that the leaf has lost
its freshness, and is often torn and
withered, having clearly served its pur-
pose for the plant which bore it. In
compound leaves like the Common Ash
and Horse-Chestnut a separation-layer
is formed, not only across the leaf-base,
but across the bases of the leaflets as
well.

Fig. 41 is a longitudinal section of
a Sycamore twig through a node, and
at s.l it is seen that the separation-layer
(or absciss layer) is already formed before
the leaf falls. Notice that cork has not formed across the
vein (v) . This is kept open to the last, for along it much
of the nutrient material is passed backwards into the stem
before the leaf is finally snapped off by the wind.

The tissues we have considered not only form the struc-
ture of the shoot, but it is by their means that the work of
the shoot is carried on. It will be of interest to determine
something of this work. How and under what conditions

Fig. 42. Part
of Sycamore

Twig. — /, lenticel;
s, leaf-scar ; s.l,
separation-layer.

74 THE VEGETATIVE ORGANS

is it performed ? Do changes in any of the conditions affect
the behaviour and growth of the shoot ? Are the differences
we find in the form and structure of plants growing in
different habitats correlated in any way with the differences
in their environment ? These are problems we must now
endeavour to solve.

CHAPTER VII

WORK OF THE SHOOT

We have seen in the experiments with germinating seeds
that the main shoot grows upwards towards the light, in
the direction opposite to that of the main root, the stimuli
producing this result being gravity and centrifugal force.
We must now extend our knowledge by making one or two
further observations with older plants.

Perception of and response to stimuli. — Lay on its side
a plant of Geranium (Pelargonium) or Balsam in a hori-
zontal position, as in Fig. 43. Note at intervals the beha-
viour of both stem and leaves (a-e) ; the stem-tip turns
upwards and continues to grow vertically. Take another
actively growing plant, lay it on its side for an hour, then
place it in a normal upright position and observe its mode
of growth. Does the tip show signs of turning while lying
horizontally ? Does any subsequent bending take place ?
We see that the stem, did not bend during the short time it
lay in a horizontal position, but bending does occur later,
even after the plant is placed upright. This experiment
shows that a stimulus was received, though response was
not immediate ; and it is clear that the stimulus persists
for a time, as bending occurs even in the altered position of
the plant.

WORK OF THE SHOOT

Fig. 43. Shoot of Balsam placed horizontally, showing
Successive Phases of Curvature (a to e) (Pfeffer).

Fig. 44. Plant placed in a Horizontal Position and revolved

SLOWLY BY MEANS OF A KLINOSTAT (Jost).

THE VEGETATIVE ORGANS

A few trials will enable you to determine the time required
for the stem to perceive the stimulus, and also that required
for curving. If a plant is fixed in a klinostat (Fig. 44), and
caused to revolve in a horizontal position, the stem, like

the root, does not curve,
since it receives the stimulus
equally on all sides.

Force exerted by a growing
stem. — Just as roots exert
much force in their down-
ward growth in response to
the stimuli of gravity and
centrifugal force, so in the
reverse direction do shoots,
and their lifting power is
considerable. Obtain a
spring-balance, attach a
weight, and arrange it as in
Fig. 45, over the stem of a
Bean seedling so that the
weight is raised as the stem
elongates. Fix the weight
firmly to the hook so that
it is not readily tilted, and
determine the lifting power
of the shoot. In the experi-
ment illustrated, the shoot
in three days supported a weight of seven ounces.

Stimulus of light. Heliotropism. — Consider next the
heliotropism of the shoot.

Place a plant in a window so that light falls on it on one
side only, and note the behaviour of both stem and leaves
(Fig. 46) . In what direction has the stem turned ? Which
is the longer side of the stem, the one facing the light or the
one which has grown in the shade ? Has the light hastened

Fig. 45. Experiment to de-
termine the Lifting Power of
a Shoot.

Fig. 46. Seedlings turning towards
the Light.

Fig. 47. Bean Seedlings. — 1, grown in the light ;
2, grown in the dark.

WORK OF THE SHOOT 77

or retarded growth ? These experiments show that shoots
are sensitive to light, and that their growth is retarded
by it. Thus shoots turn to the light because they grow
more quickly on the shaded than on the illuminated side.
Such movements of plants due to the stimulus of light are
called heliotropic movements. And since shoots turn
towards the light they are positively heliotropic. Note
that the leaves also turn their blades towards the light.
The leaves of some plants, however, grow erect and expose
their tips and edges to the light, e.g. the Iris, Daffodil, and
Hyacinth ; 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 the dark (Fig. 47, 1 add 2). Compare them as to
colour, length of internodes, and size of leaf. Measure them
day by day, compare their behaviour and plot the results
in curves on squared paper as in Fig. 48.

Etiolation. Conditions necessary for the formation of
chlorophyll. — 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 etiolation (Fr. e'tioler = to
blanch). Shoots grown under ordinary conditions of light
develop the green pigment 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. Pine 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-culture experiments

THE VEGETATIVE ORGANS

that iron is essential. The shoots grown in solutions from
which iron is excluded are a sickly yellow colour (Fig. 25, c).
Further, a supply of oxygen and a suitable temperature are
also requisite. If 3^011 examine the young shoots of plants as
they emerge from the soil in the cold early spring, you will
find they are often very pale, and contain little chlorophyll.

24-
22
'20
16
16
1+
12
10
8
6

JC2

1 | 1 1 1 1 | | | [ | | | [ | 1 1 i/jb

~~1

~t_

± L

1 J

l Za

t -Z

£ __^7

/ ^

Z ^

^.s ^"

-~*k-- —

Days

10 12 14- 16 18

Fig. 48. Growth Curve of Bean Seedlings.
a, in the light ; b, in the dark.

The conditions necessary for the formation of chlorophyll
are light, warmth, and a supply of oxygen and iron.

We are now in a position to realize some of the most
general 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 endeavour
to find out the importance of these peculiarities of a shoot.

WORK OF THE SHOOT

Photosynthesis

Carbon as a plant food. Photosynthesis. — Take a series
of jars (1-5) similar to that shown in Fig. 49. In (1) place
a little water and charge the bottle with sufficient carbon
dioxide to extinguish a taper. Put in this one or two
green leaves and close securely ; then expose to bright
sunlight. Prepare the other bottles in the same way, but
in (2) place leaves that have been killed by boiling ; in (3)

Fig. 49. Experiment to
show that Green Leaves
exposed to Sunlight absorb
Carbon Dioxide.

Fig. 50. Experiment to
show that Shoots of Water-
weed exposed to Sunlight
give off Oxygen.

living non-green roots ; in (4) carbon dioxide only, as
a control, and in (5) the same as in (1), but let this be kept
in the dark while the others are exposed to sunlight.

Leave these for a day or two, then test each (a) with
a lighted taper for oxygen and (b) with lime-water for
carbon dioxide. Under what conditions has carbon
dioxide disappeared and oxygen taken its place ?

From this experiment we learn that green leaves under
the influence of sunlight are able to take up carbon dioxide

80 THE VEGETATIVE ORGANS

and give off oxygen, whereas non-green, living parts or
green leaves kept in darkness are unable to bring about
these changes. This absorption of carbon dioxide by green
plants under the influence of sunlight is called photo-
synthesis (Gr. phos, photos = light, synthesis = a putting
together), or carbon-assimilation.

That plants do give off oxygen under such conditions
as above described may be shown by an experiment
arranged as in Fig. 50. Take a jar or beaker filled with
tap-water and saturate the water with carbon dioxide.
Place in the water a branch or two of Canadian Waterweed
(Elodea canadensis), with the cut ends uppermost, and over
these a funnel with a shortened stem. Completely fill
a test tube with water and invert it over the stem of the
funnel ; then expose to sunlight. Set up a similar experi-
ment, but instead of charging the water with 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 it so as to remove all the free carbon dioxide.
Place the bottles side by side and compare.

In the second case it will be found that few or no bubbles
are given off, but in the former, bubbles are given off freely
and displace the water in the inverted test tube. When
sufficient gas has accumulated, test it with alkaline pyro-
gallic acid and note how suddenly the brown colour is
produced, or insert a glowing match which at once bursts
into flame ; these are proofs that the gas given off is oxygen.
We thus see that such a plant, when growing in water
containing carbon dioxide, and exposed to sunlight, gives
off oxygen.

Formation of starch in green leaves. Starch 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 its appearance and under
what conditions it is formed. For this purpose, plants of

WORK OF THE SHOOT

the cultivated Geranium serve very well. Keep a plant
in the dark for a day, then partially cover two or three
of the leaves while still on the plant with black paper,
tin-foil, cardboard, or pieces of cork, as shown in Fig. 51, 1,
in such a way that light is excluded from one part of the
leaf while the other may be illuminated. Place the plant
so prepared in sunlight for several hours or, if more con-
venient, on two or three successive days. At the end

Fig. 51. Experiment to show that Starch is formed in
Green Leaves when exposed to Light. — 1, leaf covered with
opaque paper, from which a cross has been cut ; below is a cork
pinned to the leaf to exclude the light ; 2, the same leaf when
tested later with iodine solution ; the shaded areas contain starch.

of a period of several hours' illumination 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 which means the green
colouring matter is gradually extracted. (This may be
hastened by boiling in alcohol, but it must be done very
carefully to prevent ignition of the alcohol vapour.) The
resulting colourless leaves should be washed in water, then
laid out in a shallow dish and covered with iodine solution.

1298

82 THE VECxETATIVE ORGANS

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 which
were exposed to light take on a blue-black colour (Fig. 51,2),
indicating the presence of starch, which appears only
in those parts to which light had access.1

Conditions necessary for the formation of starch. — A
similar test should be made with leaves of a variegated
Geranium, one with white patches on its leaves being
selected. The leaves need not be covered, but after exposing
the plant to sunlight as in the previous experiment, test
for starch by the same methods. It will be seen that
starch 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.
Place a little caustic potash solution in the bottom of
a bottle, tilt it as in the figure and turn into it a leaf of
the plant, taking care that the leaf does not touch the
liquid. Close the bottle with a split cork perforated to
admit the petiole without injuring it, carefully seal the
cork 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 composition of the air by the
action of a gieen leaf ? Test the leaf as above and deter-
mine whether starch has been formed under the conditions
of this experiment ? We have seen that plants absorb
oxygen from the air and give off carbon dioxide ; this
is the process known as respiration or breathing ; also
that a green leaf exposed to air containing carbon dioxide

1 If it is necessary to carry out these experiments during very
dull weather, satisfactory results can be obtained by exposing the
plants to artificial light, care being taken not to injure the plant
by heat.

WORK OF THE SHOOT

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. Experiment to show that a Leaf of Pelargonium
exposed to Light in Air devoid of Carbon Dioxide does not
form Starch.

of bringing about chemical changes resulting in the forma-
tion of starch. But starch is found only in those parts
of leaves which contain the green pigment chlorophyll,
and the experiment just performed proves to us another

F 2

84 THE VEGETATIVE ORGANS

important fact, namely, that a green leaf, working under
normal conditions, but in air devoid of carbon dioxide,
is unable to form starch. In addition to the above condi-
tions it is found that the work of a leaf can only proceed
at a suitable temperature and when the plant is able
to 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 that
starch is formed in green leaves only under the influence
of sunlight, and not in parts that do not contain chloro-
phyll, yet we found an abundance of starch in the
cotyledons of the Bean and in the endosperm of the Wheat
and other grains ; and it also occurs, as we shall see, in the
non-green parts of stems and roots. It is obvious, therefore,
that starch arises in more ways than one within the tissues
of a plant.

Now the starch grains formed in green leaves are
formed entirely from inorganic substances ; the exact
method is not known, but a possible explanation is the
following :

C02 + H20

= HCOH + 02

(carbon dioxide) (water)

(formaldehyde) (oxygen)

6HCOH

= C6H120,.

(formaldehyde)

(sugar)

w(C6H]206) -

nU20 = (C6H10G>

(sugar)

(water) (starch)

In words, the carbon dioxide and water within the living
chlorophyll-containing cells of the leaf, and under the
conditions already enumerated, may be split up and their
constituent atoms rearranged to form a compound called
formaldehyde and also the element oxygen. This will

WORK OF THE SHOOT 85

account for the carbon dioxide taken in and the oxygen
given out during photosynthesis. Six molecules of formalde-
hyde are now supposed to combine to form sugar. By
further action the sugar is deprived of a molecule of water
and 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 quite incapable of
being transferred from cell to cell in this form. Obviously,
if the grains are not removed, the cell will soon reach its
limit of activity in this direction.

Starch digestion. — The following experiments will help us
to understand how the transference of food-materials is
brought about. Place a little potato starch in a beaker, add
water, and note that the starch grains are not dissolved. On
boiling the liquid for a few minutes, a mucilage is produced,
but the starch does not completely dissolve. Dilute this
with cold water. Place a little of the cooled liquid 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 the
tube firmly in the left hand while the following experiments
are carried out. To another portion of the weak mucilage
add a little diastase or malt-extract (which contains
diastase), and allow it 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 little grape-sugar, add
water to it, and note how readily the sugar dissolves. Take
a small portion of this, test it with iodine solution, and
note that no violet coloration results. To the remaining

86 THE VEGETATIVE ORGANS

portion add Fehling's solution ] and boil. Note the deep
orange colour produced. This reaction is characteristic of
grape-sugar. Test by the same means (i) the juice of the
Grape and (2) a few small pieces of Onion and compare the
results. Grape-sugar occurs abundantly in each case ; it is
of common occurrence in plant tissues, and is a valuable
and easily transported food. Now examine the starch
mucilage which has been acted upon by the saliva. Note
that the mucilage has dissolved. Test a small portion with
iodine solution. Is starch present ? As no violet coloration
results, we may conclude that the starch has been converted
into some other substance. To the remainder add Fehling's
solution and boil. What is the new compound formed ?
From this experiment we learn that saliva contains a
substance which has the property of converting starch into
sugar. Such a body is called a ferment or enzyme, and it
is by means of such ferments that we are able to digest
the starch present in our food. The starch-digesting ferment
in saliva is called ptyalin. Apply these tests to the solution
acted upon by diastase and compare the results. In this
case 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 corroded
and disorganized, and finally converted into sugar.

We have seen above that sugar is formed in green leaves
during sunlight. Part of this is converted into starch
grains within the cells of the leaf ; the rest is drained away
to the stem or other parts. In these organs it may either
(1) be converted into starch and stored, or (2) serve for the
nutrition of tissues that are growing. At night, when the

1 Fehling's solution may be prepared and kept in two stock solutions
as follows : (1) dissolve 35 grammes of cupric sulphate in 200 c.c.
of water; (2) dissolve 70 grammes of rochelle salt in 200 c.c. of
a 10 per cent, solution of caustic soda. When required, make a
solution of equal volumes of 1, 2, and water.

WORK OF THE SHOOT

influence is withdrawn, and photosynthesis is not going on,
the ferment diastase is actively at work digesting the starch
in the leaves, and the sugar thus formed is drained away
to other organs. On the return of sunlight, the leaf is again
ready to continue the work of photosynthesis. We thus see
how a plant utilizes the alternating periods of day and night.

Starch formed from sugar in the dark by leucoplasts. —
By osmosis the sugar solution so formed in the sap is
transferred from cell to cell and carried downwards through
the leaf-stalk to the stem, and even to the root ; and in
plants developing their seeds it is conveyed to the cotyle-
dons, e. g. the Pea and Bean, or to
the endosperm, as in the Wheat.
On reaching these organs the sugar
is once more converted into starch
grains ; thus the surplus organic
food is transferred to storage organs
and there laid by until required.

In the inner parts of plants,
where light cannot penetrate, are
often found small, rounded, colour-
less bodies having the same origin
as chlorophyll corpuscles and

known as leucoplasts (Gr. leukos = white). Owing to the
absence of chlorophyll they are unable to manufacture
starch from carbon dioxide and water, but can build up
starch grains from sugar carried to them from the green
parts. In this way starch grains arise in parts that grow
in the dark (Fig. 53). If, however, tissues containing
leucoplasts, e.g. potato tubers, are exposed to light, the
leucoplasts develop the green pigment and become chloro-
phyll corpuscles. Thus, by the action of green corpuscles,
solid food-substances are formed during sunlight. These
are rendered soluble by ferments and can be transferred
to organs where they may be reconverted by white
corpuscles into solid food-reserves.

Fig. 53. Cells of the

Potato containing

Starch Grains.

88 THE VEGETATIVE ORGANS

Chlorophyll, the green colouring matter of plants, is
a very complex nitrogenous substance. As we have seen
(p. 81) it may be extracted by means of alcohol, and if
sections of leaves so decolorized are examined under
the microscope the corpuscles will still be found in the
cells (Fig. 29, 5 cli). In the living plant the pigment is
probably dissolved in some oil, and this solution is enclosed
in the meshwork of the corpuscles. Each chlorophyll
corpuscle or chloroplast, therefore, consists of (a) a proto-
plasmic body or plastid and (6) a pigment, chlorophyll.

Light rays absorbed by chlorophyll. — 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 light
by means of a spectroscope and note the band of colours —
red, orange, yellow, green, blue, indigo, and violet. This
band is called the spectrum of white light. Place an
alcoholic solution of chlorophyll in the path of a beam
of light before it reaches the slit of the spectroscope ;
note the spectrum which results, and compare it with
that of white light. Observe the dark bands produced
and note carefully their position in the spectrum. Seven
vertical bands are produced, but some of them are difficult
to 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 in
the yellow and green. We thus see that the rays of light
falling on a green leaf do not all pass through it. Chloro-
phyll 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 thus
absorbed from the sun's rays that enables the chloroplasts
to carry on the constructive work of photosynthesis. We
are now able to understand why starch is not formed in the
white parts of leaves or in green leaves kept in darkness.

WORK OF THE SHOOT 89

Currents in the stem. — Let us now perform a few experi-
ments which will enable us to determine the channels
along which travel the materials used by the shoot.

Place in a bottle red ink or a solution of eosin, and obtain
shoots of Rhododendron, Ivy, or similar evergreen. Place
the freshly-cut ends of the 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. Place a similar
shoot in another bottle, but instead of eosin, use water to
which a little 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 produce
a 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 from
the lower end of each and compare the cut surfaces. How
do they differ ? Cut off a piece two inches long and split
it longitudinally 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 whether
it extends into the leaves. Cut the leaf-stalk and leaves
across and note whether they are coloured ; and, if so, how ?

What do we learn from these experiments ? We find
that the shoots in eosin have taken up the 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 these
tissues have been removed the eosin has ascended, not-
withstanding their removal. The shoot in carmine,
however, remains uncoloured. Why ? Here the fine
particles of carmine are in suspension, not in solution,
and although a coloured solution like eosin may be
absorbed, the particles, even so fine as those of the
carmine, are unable to pass through the woody tissues.

THE VEGETATIVE ORGANS

Water, however, is absorbed and serves to keep the shoot
fresh, while that in eosin becomes discoloured and dies.
Judging from these experiments we may conclude that
the wood of such a shoot is the path along which water
ascends through the stem to the leaves. But what of the
other tissues of the bundle, for example the bast ?

If we examine the plants in a garden or park, especially
shrubs or trees which have been tied for some time to
a support, it will be interesting to note
the mode of growth in the neighbourhood
of the ligature. Fig. 54 is a sketch of
a rose stem which has been tied in this
way and allowed to grow for some time
without further attention. Careful ex-
amination of such a shoot shows that, as
the stem has grown in thickness, the
ligature has gripped it with increasing
pressure, and the delicate tissues of the
inner cortex and bast have been so com-
pressed that substances could not pass
along them, but the rigid walls of the
woody tissues have withstood the pressure,
and sap can still ascend as usual. The
chief changes noted, however, affect the
portion of the stem above the ligature,
materials have accumulated, obviously
carried from a higher level, and have become stored in
an abnormal tissue which forms a swelling.

Fluids are able to travel not only upwards through the
wood and downwards through the bast, but there are many
cross-currents as well, especially through the thin plates
of tissue, the medullary rays, passing from pith to cortex.
In some stems these tissues become loaded with food-
materials carried to them from leaves and other parts.
This is seen very clearly in the Clematis. Obtain a piece

Fig. 54.

Ligatured Stem

of the Rose.

Here nutrient

WORK OF THE SHOOT 91

of stem about the thickness of a lead pencil and cut several
slices across it. Lay them on a glass slip and place on them
a drop of iodine solution. By means of a pocket lens
examine the surface and note the effect of the stain.
Compare the yellow-brown walls of the wood with those
of the medullary rays and with the outer cells of the pith.
These are crowded with dark purple-stained starch grains.

CHAPTER VIII

WORK OF THE SHOOT {Continued)

Transpiration. — It is a matter of common observation
that, when plants are grown under a bell-jar or in a glazed
case, the sides of the chamber are covered with drops of
water. Where has this water come from ? Has it come
from the soil or from the shoots ? If from the latter,
seeing that a plant is provided in its roots with so excellent
a means of obtaining water, why should so much be thrown
off by its shoots ?

A simple experiment will enable us to decide the matter.
Plant in a pot a single rosette of London Pride, take a piece
of lead-foil large enough to cover the top of the pot, cut it
from one side to the centre, bring the two cut edges round
the stem beneath the leaves and fold them closely over,
pressing the sides around the pot so as to exclude all
moisture from the soil (Fig. 55). Take a small vessel,
fill it with dry calcium chloride (a substance which
readily absorbs water), and weigh it carefully; place this
on the top of the lead-foil alongside the plant, and cover
the whole with a bell-jar, sealing the edge with vaseline.
Allow this to remain for a day ; then examine. Remove
the bell-jar and note what change has taken place in the

THE VEGETATIVE ORGANS

contents of the vessel. Weigh again, and note the difference.
To what is this increase due and whence has the water
come ? This giving off of water by living shoots is called
transpiration. A vessel with the dry calcium chloride
weighing together 16 grammes has been found by experi-
ment to have gained I gramme in weight in twenty-four

hours ; i. e. the leaves have given off
during twenty-four hours i gramme
or i cubic centimetre of water.

If this water has come from the
leaves, has it come equally from
the two surfaces, and are leaves
similar in this respect ? To deter-
mine these points, prepare a few
sheets of cobalt paper by dipping
pieces of filter-paper in cobalt
chloride solution and allowing them
to 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-
posed to ordinary air or when
breathed upon. Obtain a dry duster,
fold it several times so as to make
a pad, and lay on it a few leaves,
some with the lower, others with
the upper surface to the duster.
Place over these a sheet of dry (blue) cobalt paper, and
cover immediately with 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 it likely that the differences noted can be

Fig. 55. Experiment
to determine the
Amount of Water
given off by a plant.
—a, vessel containing
calcium chloride.

WORK OF THE SHOOT 93

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 other with vaseline. Carefully weigh each ;
then expose both to air for half an hour or more, and weigh
again. What difference do you find ? How does this
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 given time.
To do this, arrange an experiment as shown in Fig. 56.
Take a wide-mouthed bottle provided with a tight-fitting
rubber stopper with three holes. Through one is passed
the tube of a funnel provided with a tap. Through the
second is passed a bent, thick-walled capillary tube,
passing only to the lower level of the stopper. Behind
the tube is a scale marked in inches or centimetres. Through
the third hole is passed a shoot which has previously
stood in water (Rhododendron or Laurel will answer very
well). Fill the bottle completely with water and press
the stopper, together with shoot and tubes, firmly into the
bottle. If the tap of the funnel is open, water rises in the
tubes. Now close the tap and fill up the reservoir. By
opening the tap, water flows along the bent tube and drops
from the open end. Now close it, and the water stops
immediately. As the shoot absorbs, water is drawn back
along the tube and readings may now be made. Care
should be taken that the temperature is fairly constant.
Obtain the capacity of the tube and determine the amount
of water absorbed in a given time.

By turning the tap, the tube may be refilled and the

THE VEGETATIVE ORGANS

experiment repeated or varied in several ways ; e. g. by
coating some of the leaves with vaseline (i) on their

FlG. 56. POTOMETER, TO MEASURE THE RATE OF

Transpiration in a Shoot (Farmer).

upper and (2) on their 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.

WORK OF THE SHOOT 95

The food of plants, taken up by the roots, is absorbed
as very weak solutions, and one of the great functions of
leaves is to get rid of surplus water. The rate of transpira-
tion varies in different plants and under different conditions ;
there are many peculiarities and exceptions, but generally
the circumstances which favour transpiration are : (1)
winds ; (2) warm air ; (3) height of the plant above
ground, the upper layers of the atmosphere being drier
than those near the ground ; (4) numerous leaves, large
leaf-surface, and many stomata. On the other hand,
transpiration is reduced : (1) in calm weather ; (2) when
the air is cold ; (3) in plants which are low-growing ; and
(4) in plants which have fewer leaves, smaller leaf-surface,
and fewer stomata.

Protection of stomata. — For a shoot to perform its func-
tions in a satisfactory manner it is important that the
stomata should not become blocked by rain or dew, and
it is interesting to determine how leaves are protected
from this danger. Dip the leaves of several common plants
in water, then take them out and examine both upper and
lower surfaces. To what extent are they covered with
water ? Has immersion resulted in blocking a considerable
proportion of stomata ? What are the peculiarities of
surface-structure which prevent the surface from becoming
wetted ? Not only is the leaf practically non-absorbent,
but surface coverings such as hairs and wax render wetting
difficult or impossible. Repeat these experiments with
leaves of Pinks or Carnations ; note the blue-grey coating
of wax or ' bloom ' and see how easily it may be wiped
off. Dip a leaf in cold water, note the silvery-looking air-
cushion on the surface ; then remove it. Is it wet or dry ?
Dip another leaf into hot water, note what happens to
the bloom ; remove the leaf and compare it with a fresh
one. Bring the flame of a match near an uninjured leaf
and note the effect of heat on the bloom. Other leaves

THE VEGETATIVE ORGANS

(and many fruits) provide similar examples, and in each
case we find that the waxy coating very effectually prevents
the surface from becoming wetted. Further modifications
will be noted in connexion with the habitats of plants.

In the familiar process of wilting we have another good
illustration of transpiration. Take two shoots and place
the freshly-cut end of one in water, but allow 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 has
become limp, i. e. the shoot cut off from its water-supply

Fig. 57. Experiment to illustrate Turgidity.— i, piece of
Daffodil stalk ; 2, cut into two strips ; 3, cut into four strips ;
4, the same in water.

has wilted. Similarly, if a plant rooted in the soil be
insufficiently watered it wilts, i. e. its shoots and leaves
become limp and droop ; but such a plant soon regains
its freshness and turgidity on being watered.

Turgidity. — A simple experiment will help us to under-
stand this. Take a piece of the flower-stalk of the Dandelion
or Daffodil, about three inches long, and cut it down the
middle, as in Fig. 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 longer
side, in what condition were the tissues of this surface
before the stalk was cut ? Clearly they were compressed,

Fig. 58. Excretion of Water by Wheat
Seedlings.

Fig. 59. Leaf-Rosette of a Saxifrage. — The margins of the leaves
are encrusted with lime from chalk glands at the ends of the teeth.

WORK OF THE SHOOT 97

and, being released from the rest of the stalk, have expanded.
Make another cut, at right angles to the first, and note the
result. Now place the cut end in water and note what
happens. The inner surfaces have become still more
convex.

Our previous experiments in osmosis will help to explain
this. The water, through the attraction of the cell-contents,
has been absorbed by these cells, increasing the internal
pressure and stretching the elastic cell-walls. The dis-
tension of the cell by the internal pressure of sap in plants
is called turgidity. Next place the cut stalk in strong
salt solution and note the change in shape. The salt
solution, attracting water from the cells, reduces the internal
pressure ; the walls contract, the cells become smaller,
and consequently what was before the convex side becomes
now the concave side. Wash the cut stalk thoroughly in
water, and allow it to remain in water a short time. Do the
cells regain their turgidity and the strips resume their
former shape ? It is by such changes in the internal
pressure of the cells of plants that shoots are at one time
fresh and turgid, at another limp and wilted. The pith cells
of herbaceous stems, and of quick-growing shrubs, show
the same tendency to elongate, and though unable to do
so, owing to the resistance of the surrounding woody tissue,
they help considerably to maintain the rigidity of the
shoot.

Root-pressure. — We have already seen, in our observations
on Wheat seedlings (p. 33), that the roots may absorb more
water than a plant can utilize in a given time, and that
the excess is forced out of the tips of the leaves (Fig. 58).
Drops of water may often be seen on the leaves of certain
plants in the early morning, e. g. on the leaf-teeth of
Fuchsia and Lady's Mantle, and at the ends of the main
veins in the Garden Nasturtium. Sometimes the salts
in solution are so abundant as to leave a deposit on the leaf

1296 r-

98 THE VEGETATIVE ORGANS

when the water evaporates ; this occurs in Wheat seedlings,
and especially in some Saxifrages, where the salts form
chalky incrustations on the ends of the teeth (see Fig. 59).
Water is usually given 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 night the stomata close, but
absorption of water by the root goes on ; the plants
become turgid, and as the amount absorbed exceeds the
amount of water- vapour transpired, water in a liquid
state is forced out of the leaves. Some leaves, e. g. the
Garden Nasturtium, have special stomata which are
permanently open for this purpose and are called water
stomata.

Obtain an actively growing plant of Sunflower, Fuchsia,
or Dahlia, cut off the shoot about three inches above the
soil, dry the cut end and examine the surface with a pocket
lens. Soon water exudes from the cut surface. Arrange
an experiment as shown in Fig. 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 will be forced
upwards. By this means the pressure of exudation may
be measured. The pressure which exists in the tissues 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 plants
in spring is often very great. If, for example, the stem
of the Vine is cut as the leaves are unfolding, so great
is the flow of sap, that it can only with difficulty be
stopped. This exudation of sap is known to gardeners
as 'bleeding'.

Force of transpiration. — It is obvious that considerable
force must be exerted in drawing water up a stem to the
leaves to replace that given off as water-vapour through

WORK OF THE SHOOT

the stomata. Some idea of this force may be obtained
from the following experiment (Fig. 61). Take a long,,
thick-walled glass tube fitted at one end with a rubber

Fig. 60. Experiment
to show the pressure
of Exudation (Jost).

Fig. 6i. Experiment to
demonstrate the Suction
Action of Transpiration

(Jost).

stopper. Through a hole in the centre push the end of a
Laurel shoot, selecting one thick enough to fit tightly.
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

ioo THE VEGETATIVE ORGANS

secure the tube with the shoot to a retort-stand or other
suitable support. Fix a scale to the tube and take readings
at intervals. When the mercury has reached its maximum
height, ascertain the weight of the column of mercury
raised by the force of transpiration.

After a time, 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 liquids has resulted in air being drawn
through the stem, and that this has accumulated on the
top of the column ? Or did the water contain air which
may have risen to the surface ? The value of the latter
suggestion may be tested by using water which has been
previously boiled and allowed to cool. If air then accumu-
lates 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-pump
firmly to the water-tap and connect it to a bottle by means
of thick-walled rubber tubing. Fill the bottle with water
and insert a rubber stopper, through the hole of which
is passed the stem of a Laurel or the stalk of a single leaf,
as shown in Fig. 62. Turn the tap gently, then steadily
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 shoot ?

This experiment may be reversed. Place the leaves
in the water and the cut end of the shoot in the air;
observe the air-bubbles coming out from the numerous
tiny points on the under surfaces of the leaves and more
vigorously at any broken or injured places. Suddenly turn
off the water and note the change of colour in the lower
surface of the leaf. Why is this ? Turn on the water again
and the leaf regains its colour. Repeat the experiment

WORK OF THE SHOOT

IOI

and notice that with the sudden back-rush of water the
air-spaces of the leaf have become filled with water. How
can it enter the leaf ? What force has been exerted to
bring about this striking result ?

The living cells of a plant are tiny chemical manufactories,
and very elaborate indeed are some of the compounds

Fig. 62. Suction of Air through a Leaf.

made there. The raw materials are carried to them in
the water from the soil and in the air which enters the leaves
and other green parts. The latter are exposed to the
influence of sunlight, and this is one of the necessary
conditions for the formation of the green pigment, chloro-
phyll ; otherwise plants would, as a rule, be sickly in colour,
as they are when grown in the dark. The presence of this
pigment gives to a shoot the power of utilizing the energy

102 THE VEGETATIVE ORGANS

of the sun's rays in bringing about and carrying on many
important changes in the substances entering the cells,
also of rearranging their component atoms and building
up new compounds from them. During these chemical
changes much heat is evolved, as we have already seen in
the experiment with germinating peas ; but the leafy shoots
of plants are always cool, and commonly cooler than the
surrounding air. How is this ? With all the chemical
changes going on in plant-tissues, why does the temperature
of the plant not rise much above that of the air, as it does
in our own bodies ? Some heat may be lost by radiation,
but for a fuller answer we must go back to our experiments
on transpiration and try to realize the enormous amount
of heat required to convert the water of the cell-sap
into 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 dissipated
in this 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 its artificial representative, a water-culture solution)
a dense, or a weak, food-solution ? Is it necessary for the
solution to be a weak one ? and, if 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-solution. This involves the absorption
of an excess of water above that needed for the building
up of tissue-materials. Hence we see the value of a thin,
flat leaf whose exposed surface is very large compared
with the amount of its tissue. Again, the spongy tissue
of a leaf, with all its cells hung out, as it were, in drying-
chambers, has an interesting meaning. These chambers,
communicating by way of the stomata with the air outside,

WORK OF THE SHOOT 103

render the whole an admirable arrangement for getting rid
of the excess of water. It seems from this that a large
leaf-surface might coincide with great absorption, involving
a large food-supply and consequent rapid growth. At any
rate this is worth keeping in mind, and it 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
ditch, a hedge, on a moor, a rock, a sandy shore ? Meanwhile,
we see how important it is that the functions of the stomata
should not be interfered with, and some of the most
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 arise 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 tightly
packed, and the parts are so small, that they are difficult
to dissect. The essential features, however, may easily be
made out from an examination of a Brussels Sprout
(Fig. 63). Each ' sprout ' arises in the axil of a leaf, like
the 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 leaf
a small bud will be found. How many leaves are there ?
How many axillary buds can you find ? When you have
removed all you can, cut the remainder of the bud (the

io4

THE VEGETATIVE ORGANS

' heart ') longitudinally into halves and make out by
means of a pocket lens the end of the axis or growing-point,
covered over by many tender, undeveloped, or rudimentary
leaves. Such a bud is clearly a condensed, immature
branch-system, consisting of a central axis, which bears

Fig. 63. Brussels Sprout in Vertical 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 little that, when the
plants are full grown and ready for market, they still bear
all the characteristics of huge buds. They are not protected
on the outside, however, by tough scales, and are hence
called naked buds. It will be interesting to compare with

BUDS AND BRANCHES

105

these such plants as the Daisy (Fig. 64), Dandelion, Plan-
tain, Primrose, and London Pride, or other Saxifrage
(Fig. 59), where the leaves all spring close together round
a short stem and quite near the ground. Each resembles
a bud which has opened out its leaves and by pressing
them out in a close rosette has secured a little patch of
ground for itself. The leaves of such plants should be
drawn and the peculiarities of outline noted. In the Daisy

Fig. 64. Daisy, showing Reproduction by means
of Offsets.

and London Pride the leaves are spoon-shaped (spatulate) ;
in the Ribwort or Plantain they are lanceolate ; and in
the Primrose they are obovate and wrinkled. The margins,
too, are peculiar, being even or entire in the Daisy and
Plantain, wavy in the Primrose, and edged with small,
rounded lobes (crenate) in the London Pride ; while the
margin of the Dandelion leaf has large teeth pointing
backwards (runcinate), which have earned for the plant
its popular name.1 The tips of the leaves, too, vary from
blunt and rounded in the Daisy to sharp-pointed or acute

1 Dandelion is a corruption of Fr. Dent-de-lion.

io6 THE VEGETATIVE ORGANS

in the Ribwort. Note the differences in the length of the
leaf-stalk and the size of the blade from the lower and outer
to the upper and inner part of the rosette, and observe how
this 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 from
leaves rising, like those of a Stock, on a taller stem above
ground and known as cauline leaves. The habit of forming
rosettes 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 other
habitats, especially in grassy swards. As the buds which
arise in the leaf-axils of such plants also tend to form rosettes
close to the parent, a large cushion is in time produced.
Short lateral shoots of this kind are called offsets, and they
serve as an important means of vegetative reproduction
(Figs. 64 and 257).

If opportunity offers, it will be interesting to study the
various rosettes of the plants growing on a rockery. You
will find many forms, some compact, others lax. There
will 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 thick indeed and
able to store much water for use in times of drought.

Observations on opening buds. — If you place winter shoots
of trees in water for a few weeks you will be able to watch
the opening of the buds, and it is easy to study the more
important details of their structure. In such opening buds
observe : (1) the number and arrangement of bud-scales ;
(2) their origin from leaves, leaf-bases, or stipules ; (3) the
transition from bud-scales to foliage-leaves ; (4) the
arrangement and manner of folding of the foliage-leaves ;

(5) whether the leaf-stalk 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 107

Try to realize the great amount of work which is going on
as the buds open, and to determine where the material
comes from and how it is utilized. If opening buds are used
instead of germinating peas in the experiment we have
performed previously (p. 44), you will find that they
absorb a large amount of oxygen and give off much carbon
dioxide. It has been found that during this period of
active respiration many of our common trees lose from
20 to 45 per cent, of their total dry weight. This helps us
to appreciate the fact that respiration is a wasting or
breaking-down process.

Lilac. — Quite different from the rosette type are the buds
of the Lilac. If we watch them expanding in the spring
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. 205).
The arrangement of the leaves on the stem, and the relative
positions of leaves of different sizes, stand in strong contrast
with what we find in a typical rosette. Compare the leaves
from below upwards, and notice the transition from small
scales 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
advances, not when the bud opens, as in many trees.

Privet. — Now compare the Lilac shoot with a shoot of
the Privet (Fig. 65). Note the small, brown scales below ;
their arrangement and the varying sizes and shapes, not
only of the scale-leaves, but of the green foliage-leaves ;
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 light
falls on the shoot ? What part of the leaf is concerned in
bringing the blade into such a position ? The movement

ro8

THE VEGETATIVE ORGANS

occurs at the leaf-base. This is of common occurrence in
plants ; and the Yew, Ivy, and Virginia Creeper provide
further interesting examples. By means of a pocket lens
carefully examine the mode of attachment of the leaf to
the stem. The three parts of a typical leaf are easily
determined : (i) the swollen base, each
side running as a ridge down the stem ;
(2) the short stalk marked off from the
base by a dark transverse line, and (3)
the ovate, entire, acute blade.

Bend the leaf back and press the
bent stalk against the stem until it
snaps. Where does the break occur ?
Repeat this and notice that the dark
line is a line of separation (Fig. 65, s).
Examine older shoots for leaf-scars, and
notice that when the leaves fall it is the
blade and stalk that are thrown off, and
that the base remains on the axis as a
more or less prominent scar. Compare
other shrubs and trees in this respect,
e. g. the Common Ash.

Horse-Chestnut. — If a twig of Horse-
Chestnut (Fig. 66) be examined we may
learn much of its history. At the end is
a large terminal bud, and below this are
two large leaf-scars each showing seven
dots, which are the broken ends of veins,
while above each scar is a small bud.
Lower down, at intervals, are other crossed pairs of scars and
buds, the lowest of the series being frequently smaller than
the rest, and below these again we find a number of small
scars 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 tiny buds which, in ordinary circum-

Fig. 65. Shoot
of Privet. — l.s,
leaf-scar; s, separa-
tion-layer.

BUDS AND BRANCHES

109

stances, will not further develop but remain dormant
Thus the whole of the shoot from the
rings of scale-scars to the large ter-
minal bud has been developed during
one season from the terminal bud of
the previous year. The internodes
between the scale-scars elongate very
little, and this part of the axis remains
practically in the condition in which
it was formed, while the internodes
between the foliage-leaves greatly
elongate and separate the leaves by
considerable intervals.

Place two or three shoots in water
in the early spring and watch the buds
as they open. We are thus able to
learn a good deal about the develop-
ment of a shoot. The photographs
(Fig. 68, 1-9) are taken from shoots
so treated. The scales of the unopened
bud are covered with hairs, which
secrete a sticky mucilage composed of
gum and resin. This covers the surface
and binds the scales together, and,
with the thick scales, provides a double
protection for the young leaves within.

Watch the scales as the bud opens,
and follow their movements. At first
they are incurved and clasp the inner
leaves, later they turn outwards and
backwards out of the way, the higher,
bigger scales growing for some time
and arching over the pleated, woolly
foliage-leaves felted together with a
tangle of hairs. The stalks elongate and carry the blades

Is.

"V.

Fig. 66. Winter
Shoot of Horse-
Chestnut. — d, dor-
mant bud ; /, lenticel ;
l.s, leaf-scar; s.s, scale-
scars ; v, broken ends
of leaf- veins.

no THE VEGETATIVE ORGANS

upwards, their tips, for a time, being fastened together by
hairs, which soon fall off as the leaf grows. One by one
the leaves move outwards ; the leaflets expand and, growing
more on the upper than the under side, bend backwards
until only the upper surfaces can be seen. Growth on the
under side now quickens, and the reverse process occurs,
the leaflets being raised until they reach a horizontal
position.

When all have unfolded, examine the shoot from above
and notice that they form a closely-fitting pattern, or
mosaic. 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 smallest
blades ; 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 scale-
scars which indicate the beginning 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 after
the rest have fallen off. Then they frequently develop
little blades (Fig. 69, s), which are different from the lower
ones and are in some respects intermediate between them
and the foliage-leaves. The fact that they may bear blades
suggests that the true scales are really leaf -bases, the blades
being usually 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
it is easy to detect their scars, even on old twigs.

Usually seven leaflets are formed, which arise from the
top of the leaf-stalk, but often there are only five, and
occasionally six occur, 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. 67. Vertical Section of Bud of Pine. —
Note that the growing point is protected by overlapping
leaves ; I, leaves which bear buds in their axils.

78 9

Fig. 68. Opening Buds of Horse-Chestnut. — The shoot (5)
shows an inflorescence-scar between the branches.

BUDS AND BRANCHES

3U,

Fig. 69. Young Shoot of Horse-Chestnut. — s, leaf -blade
developing at the end of a bud-scale.

112

THE VEGETATIVE ORGANS

Fig. 70. Sycamore Buds. — 1, winter shoot of Sycamore with
a large terminal flower-bud ; 2-10, the parts of the bud dissected
out ; 2-7, one of each pair of bud-scales ; 8-9, one of each of the
two pairs of foliage-leaves; 10.. inflorescence; 11, large scale of
opening bud with rudiment of blade at the tip ; 12, 13, 14, stages
in the opening of a leaf-bud ; d.b, dormant bud ; f.b, flower-bud ;
/, lenticel; Lb, leaf-bud; l.s, leaf-scar; r.b, rudimentary blade; s.s.
1-3, scale-scars.

3
O

.—1

,3.

3
3

Li
u

L»J

fa
o

H
O

-a

t/3

(/)

cc!

-t-j

• »H

_CD

<
u
I*

Cfi

"+-I

4-1

CO*

1-1

1— 1

'3
ft

H
O
fa

CD
V3

t/D

en
O

V-i

en
CD
>

CD*

+->

bo 43

6 •

e ^

O T?

—i *~~'

en m

ii4

THE VEGETATIVE ORGANS

These observations help us to understand the true nature of
the bud-scales. The upper, large, green ones are, like those
of the Horse-Chestnut, leaf-bases bearing rudimentary
blades, while the lower, exposed ones are leaf-bases only.
Some of the earliest buds to open, however, are larger than
these and contain flowers as well as leaves (Fig. 70, 1, f.b).
When fully expanded the blades are seen to be in one
piece (simple), the five lobes not being divided into separate
leaflets 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- 73)- 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. 78), and note that in the case of the latter, similar
advantages are secured in another way, viz. by long
internodes and narrow blades.

Beech. — The bud of the Beech (Fig. 74) presents several
interesting differences from those we have examined.
Observe its long, tapering form and the light-brown
membranous scales which are arranged in pairs. Remove

I S3.]

m 3.3.2.

S.3.3.

r.3.4.

IS. 3. 5.

d.s.

raass^^

[s.s.6.

Fig. 74. Six-year-old Winter Shoot of Beech. — d s, dwarf
shoot ; s.s.i to s.s,6, scale-scars of six successive years.

n 2

n6 THE VEGETATIVE ORGANS

the outer scales and examine the inner ones carefully. You
will find between each pair a tiny green blade ; the outer
ones have no leaf -rudiment between them. Farther in-
wards are the foliage-leaves, folded fan- wise (Fig. 72), 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 careful 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, having
served 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 stipules, and not, as in the Sycamore
and Horse-Chestnut, of leaf-bases. In the case of a few
plants, e. g. the Laburnum, the scales do not fall when the
bud opens, but wither on the branch. In many plants the
stipules grow with the growth of the leaf, are green and
leaf -like, and last as long and serve the same general
purposes 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 and many herbs are not protected
by scales 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 by
a mealy covering of star-shaped hairs, hence it is sometimes
called the Meal Tree.

Watch the buds of the Beech as they open in the spring
(Fig. 75) and compare the behaviour of the leaves with
that of the Horse-Chestnut leaves. Note the elongation
of the bud, the separation of the scales, the bright yellow-
green leaves peeping above them, folded fan-wise and

*>4'»

Fig. 75. Opening Buds of Beech.

Fig. 76. Later Stage of Opening Buds of Beech ;
leaves pressed downwards by greater growth of the upper
surface.

116

BUDS AND BRANCHES 117

clothed with silky hairs. As they emerge you will see that
the leaves hang downwards in such a way as to expose
only their upper surfaces (Fig. 76), thus reducing loss of
water by transpiration and loss of heat by radiation, as
in the Horse-Chestnut. Finally, they are raised by increased
growth on the under surface and thus the blades are brought
into a horizontal position.

On comparing a given shoot with that of the Lilac we
find similarly that the lowest and oldest leaf is the smallest,
the highest and youngest leaf the largest (see Fig. 191, 2).
This difference in size, however, together with the horizontal
position of the blades, results in the leaves not only forming
a flat plate, but the available space is occupied with the
least amount of overshadowing. In this way a leaf-
mosaic is formed, but by a very different means from that
of the Sycamore or Horse-Chestnut.

These features should be looked for in other trees, such
as Elm (see Fig. 197), Hornbeam, and Hazel, and also in
herbaceous plants. Leaf-mosaics are common in the plants
of temperate climates.

Examine a winter twig of the Beech similar to that
shown in Fig. 74. Note that there is a slender zigzag
shoot at the tip with a bud at each bend. Below that,
a series of scale-scars (s.s) shows the limit of the year's
growth. These features are repeated as we pass backwards,
six such portions being shown in the figure at 1-6. At the
bends, in place of buds, are short branches with many
scale-scars and terminated by a bud. Clearly these
branches grow very slowly and the leaves produced by
such buds are separated by very short internodes. Such
short, slowly- growing branches are called Spurs, or Dwarf -
shoots. Figs. 74, 75, 76 show what is produced from such
a shoot in the following spring. The end bud has grown
into a long, slender, slightly zigzag shoot with leaves at
the bends. The next two lateral buds form the beginnings

n8 THE VEGETATIVE ORGANS

of dwarf shoots with crowded leaves, while the buds at the
ends of the dwarf shoots of previous years have each de-
veloped several leaves, also crowded together, owing to the
slow growth of their internodes. If you examine several twigs
of the Beech, you will find that, while the end bud may grow
a foot or more in a season, a dwarf shoot may have grown
only three inches in ten or more years.

Scots Pine. — An excellent example of the development
of dwarf shoots is seen in the Scots Pine (see Fig. 182).
Examine a small branch, and you will find that it is
terminated by a large bud, round the base of which are
three or four smaller lateral buds standing at nearly the
same level. Farther back the axis appears to be covered
by tough evergreen needle-leaves. Carefully examine the
shoot to see where and how the needles arise. Do they
spring, like many leaves we have seen, singly from the axis ?
Remove a few of them. Do they come away singly, or in
pairs ? Can you find any other structure on the axis still
remaining when the needles have been removed ? Examine,
and compare with this, part of a branch from which
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 similar structures ?
If any doubt as to the last -mentioned point remains, the
examination of an elongating bud in the spring will make
their relationship 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. 179) .
They remain three or four years on the tree, and are then
thrown 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 short branches also ? We see that

BUDS AND BRANCHES

119

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 pr defoliation. — In the above examples we
have seen how neatly the leaves
are packed in the bud with the
least loss of space. The manner
in which leaves are thus folded
and arranged is known as ver-
nation or praefoliation, and
their relationship may be seen
by the examination of a trans-
verse section, or more easily 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 (revolnte) ; the

Violet, Elder, Apple, Pear, and

Poplar, where they are up-rolled

(involute) ; the Plum 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

(circinate) . When revolute leaves

expand, growth is greater on

the under surface ; in involute,

convolute, and circinate leaves

growth during expansion is greater on the upper surface.

Monopodialand sympodial branching. — Trace the develop-
ment of shoots from the opening buds to the formation of

s.s.2.

Fig. 77. Winter Shoot
of Elm. — f.b, flower-bud ;
Lb, leaf-bud ; l.s, leaf -scar ;
s.s.i to s.s.3, scale-scars of
three successive years ; t.i to
t.4, dead terminal buds of
four successive years.

120

THE VEGETATIVE ORGANS

leafy branches and notice the variations in different plants.
In some trees, like the Sycamore, Horse-Chestnut, and Pine,
the terminal bud continues the growth of the main axis
from year to year. A single and continuous axis is called

Fig. 78. Branch of Willow. — d, dead terminal bud.

a monopodium. In most trees, however, growth is not
so uniform ; usually the end bud dies and the lateral
bud arising in the axil of the next leaf below enlarges,
pushes the withered bud aside, and appears to be the terminal
one. A careful study of the Elm twig (Fig. jj) will make
these points clear. In the following spring this lateral

BUDS AND BRANCHES 121

bud grows somewhat in the line of the original axis, the
terminal bud of this branch in turn dies, and is pushed
aside by the next lower lateral bud. Thus the process
is repeated, and a series of branches is superposed one on
another in such a way as to resemble a simple axis. Such
a branch system is called a sympodium. In the Willows
(Fig. 78, d), the end of the branch dies and projects as
a dead stump, while in the Hawthorn a spine may result.
These features are not difficult to make out in the autumn
when the leaves are falling and before the true terminal
bud has shrivelled and become displaced.

Long shoots and dwarf shoots. — Most of our forest trees
produce two kinds of leafy shoots, but they are not always
so well marked as in the Beech and Pine. It is common to
find, however, that the buds on a tree do not all develop
in the same manner ; some grow rapidly and produce
shoots with long internodes, others grow very slowly and
have very short internodes. Often the leaves on a dwarf
shoot vary in size and form and in the position they ulti-
mately assume. Compare the dwarf shoots of Poplar, Birch,
Beech, Elm, Hawthorn, Mountain Ash, and Laburnum.
We have noticed in many herbaceous perennials that the
axis remains short and a rosette of leaves is formed close
to the ground. When examining the shoots of trees and
shrubs observe how commonly dwarf shoots produce
flowers.

Dormant buds and stool shoots. Adventitious buds. — The
buds, which arise in the axils of foliage-leaves and scale-
leaves, are so numerous that room could not be found
for all of them to develop. The food supply, also, is in-
sufficient for the purpose. Very frequently those buds arising
in the axils of the bud-scales, and in the axils of the lowest
foliage-leaves, are very small and do not enlarge in the
spring, but lie dormant, although retaining their power
of development for a period varying from a few years

122 THE VEGETATIVE ORGANS

to twenty (see Figs. 70, 189, 194). If the growth of
the axis above such dormant buds is arrested by injury
or 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 occur
frequently on Sycamores, Oaks, and many other trees.

New buds are occasionally formed in the outer tissues
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 pith continuous with
that of the branch, while the pith of adventitious buds is
not continuous. Adventitious shoots are common on the
roots of shrubs and trees, e. g. Raspberry (Fig. 27), Rose,
and Poplar, also on the roots of Dandelion ; while some
Ferns produce adventitious buds on their leaves.

Shedding of leaves and branches. — Having now described
the structure and behaviour of buds, we may conclude this
chapter with a reference to the shedding of leaves and
branches. The shedding of scale-leaves is a noteworthy
feature in the spring, when, under Sycamores and Beeches,
the ground is covered with them. In the autumn the
foliage-leaves are thrown off and again the ground is
covered. Thus we have at least two leaf-falls in a year :
(1) A spring fall of scale-leaves ; and (2) an autumn fall
of foliage-leaves. From the Pine and often the Poplar
whole branches are thrown off. In addition there is the fall
of flowers, fruits, and their axes, so that each year a tree
sheds many of its organs.

HIBERNATION 123

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. Occasionally, however, the reverse
occurs, the roots, stems, or leaves becoming abnormally
enlarged, in which case they usually act as storage organs,
either of water, or organic food, or both. It is extremely
difficult, if not impossible, to say how these modifications
were brought about, but we can often suggest some useful
purpose they serve when once they are formed.

Adverse conditions and their effect on growth. — With the
changing seasons, plants are exposed to a great range of
conditions as to temperature, moisture, and light, which
greatly influence the power for work of the different
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 are
unfavourable 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 adverse
period the first changes we notice are the withering and
shedding of the leaves of many shrubs and trees, and the
dying down of herbaceous shoots. The strong trunks and
branches of the former persist, enveloped in their coats of
cork, whilst their buds are protected by tough, brown
scales. But how do the more tender herbaceous plants

124 THE VEGETATIVE ORGANS

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 more
favourable conditions return. But do plants hibernate ?
and if 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 winter.

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 seeds
germinate, new plants are formed, which produce flowers,
fruits, 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 either as seeds
or, 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,
like the Shepherd's Purse, may pass through their life-
cycle in a few weeks if conditions are favourable, so that
several generations may be produced in a season ; such
short-lived ' annuals ' are known as ephemerals, and
examples may often be found among the plants of
a waste-heap.

Biennials. — The Carrot behaves differently. After the
seed has germinated, the plant grows vigorously ; its root
enlarges considerably and becomes stored with a reserve
of food-materials (see Fig. 26, 1). In this condition it
passes the winter. On renewal of growth in the following
spring it produces an abundance of flowers, fruits, and seeds,
at the expense of the food stored in the root, which is
exhausted ; the seeds are shed and then the whole plant
dies after two seasons' growth To such plants the name

HIBERNATION 125

biennial is given. Beetroot and Parsnip are other examples.
The Radish and the Turnip (see Fig. 26, 2, 3) are also
biennials, but the food-material in these is stored mainly
in the greatly enlarged hypocotyl. These plants, therefore,
tide over one winter by means of their enlarged roots or
combined roots and stems, and the following winter only
their well-protected seeds remain to perpetuate the race.
Just as there are variations in the life-period of annuals,
so there are in that of biennials. If we nip off the flowers
of biennials the plants continue to vegetate for years, and
many so-called biennials, like the Foxglove and Snap-
dragon, often continue to grow for several seasons. Again,
many plants which are annuals in the plains grow for many
years in the mountains.

Perennials. — A large number of our wild plants regularly
persist from year to year and may flower each season ;
they are called perennials, and in the case of certain
trees may live to a great age. The ability to persist, and
flower at intervals through several seasons, is termed
perennation. In plants with shoots too tender to with-
stand the rigours of winter, i. e. herbaceous perennials, we
meet with many interesting forms of hibernating organs.

Underground shoots : rhizomes. — In studying a plant like
the Stock we receive the impression that the part below
ground is mainly root, but it is not easy to decide where
the root ends and the shoot begins. Pull up a plant of
either the Quick-grass (Wicks), or the Soft-grass, and
examine it carefully. What structures do you find ? Is
the whole of the underground part root ? By what
characteristics will you decide which is root and which is
shoot ? Do you find leaves on any of the parts ? If so,
what kind of leaves are they ? Can you find buds arising
in the axils of any of them ? What do these buds become ?
Trace some of them. Are these structures found on some
of the underground parts and not on others ? What are

126

THE VEGETATIVE ORGANS

the roots like, and where do they originate ? Do these
agree with the roots we found on seedling plants of the
Wheat and Maize (p. 32) ?

An examination of the underground parts of these
plants convinces us that, (1) stems bearing leaves (scale-

Fig. 79. Rhizome of Lily of the Valley. — (1) b, end bud
emerging from the soil ; /, withered leaf-bases ; sc, scale-leaf.
(2) section of bud : a, leaf-bases ; b, axillary bud which continues
growth.

leaves) with buds in their axils occur underground ; (2)
such plants may have not only underground stems but
aerial stems also ; (3) the latter are in reality branches
of the former ; and (4) the fibrous roots spring from the
stem (often from the nodes) and are therefore adventitious.

STRUCTURE OF MODIFIED SHOOTS 127

Such underground stems are known as rhizomes ; that of
the Lily of the Valley (Fig. 79) is a very instructive
one to study. Observe the nodes with their scale-leaves
and also the branched fibrous roots springing from each
node in a circle. Such an arrangement of members is
termed a whorl. Carefully dissect a bud and compare it
step by step with the parts found in other buds you have
examined. Notice the different kinds of scale-leaves :
the tough outer ones, forming a protective coat ; further
inwards some which are rather fleshy ; then the foliage-
leaves. If the bud is a large one, look for the inflorescence
in 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 monopodia!
orsympodial ? The following examples of rhizomes should
be studied and their parts compared : Garden Mint, Colts-
foot, 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.

Rhizomes 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 this habit
makes 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. At
the same time the old and decaying shoots, by adding
humus to the sand, begin the formation of a soil upon
which other plants can grow. Similar uses are made of
rhizome-bearing plants to hold together the banks of

128 THE VEGETATIVE ORGANS

canals and railways.1 In these ways the underground
parts of plants become valuable sand- and soil-binders and
play an important part as ' land-winners '.

Thickened rhizomes. — Examine the rhizome of the Solo-
mon's Seal or the Iris. The axis is greatly thickened and
bears many branched adventitious roots ; the internodes
are very short, and the scale-leaves and buds are large.
Cut a slice across the rhizome and examine the tissues.
Outside is a layer of cork, then a thick cortex, and
near the centre a number of scattered vascular bundles.
Place on the cut surface a drop of iodine solution and note
the large amount of starch stored in the cells. As the plant
grows, the rhizome tends to rise to the surface of the
ground, and if you examine Irises in a garden you will
often find that the soil is washed away from the rhizomes.
On plants which have thus approached the surface, it is
common to find thick unbranched roots which penetrate
the soil deeply, then contract and pull the rhizome down-
wards. Sometimes the growing end is directed downwards,
and as the rhizome elongates it descends until a suitable
depth is reached. Fig. 82 shows such a descending rhizome
of the Flowering Rush as it ploughs its way through the
mud in which it grows.

Stem-tubers. — The Potato is another strangely modified
hibernating organ. On the surface, which is covered with
a layer of brown cork, are small depressions, the ' eyes '.
Plant a potato, or even a thick slice of potato, in a pot
of soil, and as it grows you will 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 plants often extend their bounds,
grow between the rails, and produce a weedy track very difficult
to keep clean.

Fig. 80. Marram-grass planted as a ' Sand-binder '.

Fig. 8i. Rhizomes of Sand-sedge exposed by the Wind.

STRUCTURE OF MODIFIED SHOOTS 120.

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 form
small potatoes (t), bearing ' eyes ' like the parent, one of
which is producing a shoot (e.s). During the growth of

Fig. 82. Rhizome of Flowering Rush descending
into 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 numerous
towards the opposite or growing end, and are arranged
in a § spiral. In cultivation, banking up with earth

129G

130

THE VEGETATIVE ORGANS

induces increased formation of rhizomes and tubers, but
if left exposed to light, the tubers are small, green, and soon
develop leafy shoots. A potato plant, therefore, has three

Fig. 83. Plant grown from a Slice of Potato.: — e, 'eyes' ;
e.s, shoot growing from an ' eye ' of the large tuber ; p, slice of
potato ; rh, rhizome ; t, tubers.

kinds of stems : (1) aerial stems, bearing green foliage-
leaves and flowers ; (2) rhizomes, bearing small scale-
leaves ; and (3) from the rhizomes spring greatly swollen
and irregular stems, on which are reduced buds, the

STRUCTURE OF MODIFIED SHOOTS 131

' eyes '. Such swollen underground stems are known as
tubers. Cut a slice from a potato and test it with iodine
solution. What food-reserve is present ? make a watery
extract of a soft, sprouted potato and test with Fehling's
solution for grape-sugar.

The Artichoke is another example of an underground
stem-tuber. The food-reserve here, however, is not starch,
as in the potato, but a substance allied to sugar, called
inulin. The above must not be confused with the root-
tubers of the Lesser Celandine and Dahlia.

Corm of the Crocus. — A short, thickened, underground
stem, similar in many respects to those we have considered,
is found in the Crocus (Fig. 84, 1). In this case, however,
the stem is somewhat globular and surrounded by mem-
braneous scale-leaves (sc) ; such a stem is called a corm.
Examine a dry corm ; determine the arrangement and
mode of attachment of the scale-leaves, and remove them
from below upwards. Examine a piece of scale with
a pocket lens and observe that the fibres which form its
skeleton are parallel, with many cross-connexions. Note
the difference in length of the internodes from the base of
the corm upwards, and the circular scale-scars (s.s). Are
there any axillary buds ? At the upper end of the corm,
where the scales are crowded together, two or more buds
arising in their axils become much larger than the rest.
Cut the corm vertically in two (see Fig. 84, 3). Note the
thick, solid axis with the veins (v) passing through it, and
try to trace one of these to a small axillary bud. Place
a drop of iodine solution on the cut surface. Of what does
the food-reserve material consist ?

Dissect carefully one of the large upper buds, and com-
pare its parts with those of other buds you have examined.
Note, at the base, the membraneous scales followed by four
or five fleshy, cylindrical leaves or tunics. On removing
these, we find seven or eight small, pale-yellow foliage-

1 2

132

THE VEGETATIVE ORGANS

c.l c;2

Fig. 84. The Crocus. — 1, Crocus corm ; 2, corm with scales
removed ; 3, vertical section of corm ; 4, foliage-leaf dissected
from bud ; 5, transverse section of foliage-leaf ; 6, flower-bud
with sheath removed ; 7, corm bearing two flowering shoots,
a young corm forming at the base of each ; 8, flowering corm in
vertical section ; 9, base of corm ; 10, young corm with contractile
root; a, anther; a. r, adventitious roots ; b, axillary bud ; c.i, c.2,
c.3, corms of successive years ; c.r, contractile root ; c.s, corm-
scar ; /, foliage-leaf ; p, perianth ; s, spathe ; sc, scale-leaf ; s.b,
sheathing base of foliage-leaf; s.s, circular scale-scars ; st, stigma;
ov, ovary ; v, veins.

STRUCTURE OF MODIFIED SHOOTS 133

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, 4).
Cut a leaf across the middle and examine the cut surface,
and note the back-rolled margins and thick midrib
(Fig. 84, 5). The cells covering the midrib are crowded
with starch grains which are used up as the leaf grows ;
these cells enlarge, lose their contents and become filled
with air ; they then reflect light from their walls and give
rise to the familiar white streak of the adult leaf. In the
centre are three or more flower-buds (3), each surrounded
by a thin, membraneous sheath. Select one, remove the
sheath, and dissect the flower (6). Outside is a short, six-
lobed perianth (p), then come three stamens with short
filaments and large spear-shaped anthers (a). The ovary is
inferior 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 8), are examined,
considerable changes will be noticed in the corm. At the
base of the flowering shoots we see the beginning of a new
corm (8 c.3), formed by the thickening of the internodes
between the lower leaves. These leaves have become
withered and dead, and their ring-like bases form mem-
braneous scales around the young corm. The old corm
beneath (8 c.2), has given up much of its food-reserve of
starch, and eventually will collapse into a dead, shrivelled
mass. Thus new corms arise as thickenings of the stem of
an axillary bud of the old corm. In Fig. 84, 8 this relation-
ship is shown, but in this case we can detect the collapsed
remains of the still older corm at the base (c.i). When
the old corm is cast off, a scar is left (Fig. 84, 9) at the base
of the new one. This is a branch-scar, but, unlike the
shoots previously examined, the new branch in the Crocus

134 THE VEGETATIVE ORGANS

lives on as the plant, while the old one dies away. Round
this scar and at the lower nodes numerous fibrous roots are
given off in whorls (Fig. 84, 9 a.r). Similarly modified
stems or corms are met with in the Gladiolus.

Ascent and descent in the soil. Contractile roots. — Imagine
the Crocus repeating this process season after season, new
corms being continually formed on the top of those of the
previous year, and the mode of growth being a sympodium.
What would be the position of the corm in the soil at the
end of five or six years ? As each year's corm is developed
at a higher level than its parent, successive corms gradually
approach the surface. Now it is found that many under-
ground parts of plants have what seems to be a ' sense of
depth ', and if circumstances result in their being brought
higher or lower than their normal depth in the soil, their
behaviour is such as to raise, or lower, the young growing
shoots as required.

The method adopted by the Crocus is one of which
numerous examples may be found. Fig. 84, 10 shows a young
corm which was developed quite near the surface of the
ground ; from one side 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 pulled deeper into the soil. This process is
repeated by new roots in successive seasons until the requi-
site depth is reached. Such roots from their behaviour
are called contractile roots, and are by no means uncom-
mon ; they may be found in the Lily, Bluebell, Arum,
Dandelion, and other plants.

Bulbs and droppers. — Compare the bulb of the Tulip
with the corm of the Crocus. Cut a specimen longitu-
dinally, as in Fig. 85, 1, and note the parts of which it is
composed. On the outside are the smooth, membraneous
scale-leaves (s.i), and about four thick, fleshy leaves (s.2-5),

STRUCTURE OF MODIFIED SHOOTS 135

all springing from a very short and flattened stem ; then
follow three foliage-leaves (/.1-3), surrounding a central
flower (85, 2) with three outer and three inner petals (p),
three outer and three inner stamens (a) ; and, in the centre,

Fig. 85. Tulip. — 1, vertical section of a Tulip bulb : a, stamens ;
b, axillary bud ; /. 1, 2, and 3, foliage-leaves ; g, pistil ; p, perianth ;
r, roots ; s.i, 2, 3, 4, and 5, scale-leaves ; st, stem. 2, flower-bud
from bulb of Tulip : f.x and 2, bases of foliage-leaves ; p, perianth ;
s.i, 2, 3, 4, and 5, bases of scale-leaves. 3, Tulip bulb with dropper
in vertical section : dr, dropper ; dr.b, dropper-bud ; r, roots ;
sc, scape ; st, stem.

the pistil (g), with its three-chambered ovary, style, and
the three-lobed stigma.

If a bulb is carefully dissected or cut into a series of thick
slices from below upwards (Fig. 86, 1-4), it will be seen that
the scales and the bases of the foliage-leaves completely
surround the stem, and hence are called tunics ; while
such a bulb is said to be a ' tunicated bulb '. In the axils
of some of these leaves buds will be found (85, 1 b), which
will grow and form the bulbs of another year. We thus have

136

THE VEGETATIVE ORGANS

two kinds of leaves : (i) fleshy scale-leaves, and (2) foliage-
leaves. Unlike the corm, a bulb consists mainly of leaves.
A bulb of the Squill, the Snowdrop, or the Hyacinth
should be compared with the Tulip. In these also we have

Fig. 86 (1, 2, 3, 4). Successive Transverse Sections of
Tulip Bulb. — a, anther; /.i, 2, and 3, foliage-leaves; g, pistil;
p, perianth ; s.1-5, scale-leaves ; st, stem.

two kinds of leaves, but the bases of the foliage-leaves
persist, and become swollen with food-reserves, while the
green upper parts die away at the end of the season, leaving
a separation scar at the top of the swollen base. In the
Snowdrop, the short stem produces two narrow, green

STRUCTURE OF MODIFIED SHOOTS 137

leaves and a flowering shoot, and the bases of the leaves
thicken and store food, after which the green portions die
away.

When digging up Tulip bulbs look out for curious forms
like the one shown in Fig. 85, 3. In this case an axillary
bud has pushed its way through the old outer scale and
grown downwards in the form of a long, tubular, stalk-like
bulb. A section through this shows a small bud at the
lower end (dr.b). If such a bulb is carefully potted and
its behaviour studied, you will find that adventitious roots
are given off from the small bulb, foliage-leaves grow out
into the air, and the tubular attachment to the parent bulb
dies, leaving a young bulb at a lower level in the soil than
the parent.

Why should some buds remain short and grow alongside
the parent bulb while others elongate and push their way
deeper into the soil ? Seeing that the buds are axillary,
and therefore produced successively at higher nodes, what
would be the position of the young bulbs in the soil after
several seasons' growth ?

In consequence of this tendency 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 Tulip is to produce
down-growing buds called ' droppers ', some of which,
especially in seedling plants, may be from three to nine
inches long.

The means by which seedlings of bulbous plants descend
in the soil and eventually reach the depth requisite for
successful growth may be well studied in the Bluebell or
Wild Hyacinth. In winter and in early spring many
stages 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. 87. History of the Bluebell Bulb. — a, b, c, d, germina-
tion of the seed and seedlings ; e, young bulb ; f, g, h, i, l, different
stages of elongation of the bulbs and development of contractile
roots ; j, k, bulbs again beginning to elongate ; c.r, contractile
root; cr.sc, contractile root-scar; 5, slit in tubular cotyledon;
M, mature flowering bulb ; l.sc, leaf-scar.

STRUCTURE OF MODIFIED SHOOTS 139

leaves on the surface of the ground. Collect some of
the seedlings and study them carefully. On germination the
short radicle is carried downwards by the elongation of
the single cotyledon (Fig. 87, a and b). The tip of the
cotyledon is solid and remains in the seed, but it is tubular
below, and has a small slit (s) on one side. At the base of
the tube is the plumule, and when the first green leaf grows
it passes up the tube and out at the slit (c, d). The tip of
the cotyledon acts as a sucking organ and withdraws food
from the endosperm which is passed to the growing parts
below. The narrow green leaf is the first organ of photo-
synthesis. The food thus obtained accumulates in the
bases of the cotyledon and foliage-leaf, and in consequence
they become swollen and form a small bulb (Fig. 87, d, e).
As new leaves are formed on the stem, the bulb increases
in size and begins to'descend farther into the soil. It does
this by the elongation of its base (f to l), and soon
a curiously elongated bulb results. Often you will find
on these bulbs large contractile roots (f, g, h, i, l), which
aid in descent. As soon as the work of contraction is
completed, a separation-layer forms across the base of each
root, which then decays (Fig. 87, 1) and leaves a root-scar
on the bulb (f, l, sc. and cr.sc).

If several elongated bulbs are planted, allowed to grow
for a few weeks, and examined at intervals, you will find
that the long, outer, fleshy scale-leaves give up their food-
reserve and decay (h, i). New green leaves and colourless
scales are formed on the short stem within ; these in turn
become swollen at the base and form an oval bulb (j).
At the base of each bulb roots of two kinds are formed :
(1) slender, fibrous roots, and (2) long, thick roots which
eventually become contractile. The processes of elongation
of the bulbs and the formation and shortening of the con-
tractile roots are repeated each season until the requisite
depth is reached ; then both processes cease. At each

140 THE VEGETATIVE ORGANS

stage the bulb increases in size, and by the end of live or six
years it has become a mature flowering bulb (w). After-
wards the Bluebell reproduces itself in two ways : (i) by
means of seeds, and (2) vegetatively, by axillary buds
which form new bulbs close to the parent.

In bulbs the food is stored mainly in the fleshy scale-
leaves or leaf-bases. This food is used up in the spring as
new leaves and flowers are formed ; the old scales collapse
and die, and form the dirty, shrivelled outer coverings so
familiar in bulbs.

Geophytes. — 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 build up quickly new tissues and
complete the growth of the young organs packed in the bud.
Being situated deep down in the soil, 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
die down early, having completed their work above ground,
and after a short period of rest continue the formation 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 being
much less than we might suppose from a study only of the
parts above ground.

Plants which pass so much of their time hidden in
the soil are called geophytes (Gr. ge = the earth, phyton
— a plant). In temperate regions, the cold season is the
period of hibernation. In tropical and sub-tropical regions,
hibernation occurs during the hot dry season.

Vegetative reproduction. — Underground stems of these
various kinds provide very effective means of reproducing
the plant 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 141

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.
Vegetative 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 Silverweed (Potentilla
Anserina) appeared in a garden and was allowed to grow.
It soon produced axillary runners like those of the Straw-
berry (Fig. 88) , and by the end of the season twelve runners

Fig. 88. Vegetative Reproduction in the Strawberry. — New
plantlets arising as axillary shoots on the runners.

were produced with an aggregate length of seventeen yards,
and containing no fewer than 129 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 plantlets
instead of fruits. These eventually drop off and reproduce
the plant. Such plants are said to be viviparous (L. vivus
= alive, paro = I bring forth) .

Vivipary occurs also in species of Leek and Garlic, and
the young bulb-like plantlets on the inflorescence are called

142 THE VEGETATIVE ORGANS

' bulbils '. Axillary buds sometimes drop off and form new
plants ; good examples are found in cultivated species of
Lilium and sometimes in the Lady's Smock (Cardamine
pratensis). Reproduction by means of axillary tubers in
the Lesser Celandine has already been noticed (p. 64).

A similar mode of vegetative propagation occurs in the
Wood 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 weaker
rivals. Plants of the same species which grow in company
and cover a large patch of ground are termed social 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-grass moors, and the grassy swards of the
hills and pastures, and thus give rise to some of the
most striking features in the vegetation of a country.
The extensive tracts of Bracken in the woods and on the
hill-slopes, the blue carpets of Wild Hyacinth, and lakes
and canals choked by water-weeds, are a few examples of
the 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 life. 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 flowering
plant is fixed to the soil, all its growing parts, roots as well

MOVEMENTS AND ATTITUDES OF PLANTS 143

as shoots, execute definite movements, and even in parts

that are mature, definite movement occurs. As we have

seen, plant organs execute movements

in response to such stimuli as light, ^*

gravity, and moisture. Roots usually

turn away from the light and shoots

turn towards it ; underground stems

ascend and descend in the soil and are

aided in their descent by contractile

roots.

Nutation. Twining plants. — We have
now to notice the movement character-
istic of aerial stems. Plants growing
in woods, hedgerows, and other shady
places, tend to develop longer and more
slender stems and thinner leaves than
plants of the same species grown in open,
sunny places. If the stems of these
plants be observed it will be found that
the growing tips move in a more or less
circular orbit . ' This movement is called
nutation. Plants such as the Convol-
vulus (Fig. 89) and Black Bryony
(Tamils communis) (Fig. go) develop
long, slender internodes and relatively
large leaves, and the stems, too weak to
hold the shoot erect, lean on other and
sturdier plants for support. Their
growing tips describe a wide spiral,
making a complete revolution in from
one to two hours, and, on coming into
contact with a shoot of suitable diameter,
wind round it. As growth continues, the spiral so formed
is drawn tighter, clasps the support firmly, becomes thicker
and stronger, especially on the convex side, so that it cannot

Fig. 89.
Twining Stem of

Convolvulus
arvensis (Pfeffer).

144 THE VEGETATIVE ORGANS

untwine. Observe the direction of twining in each case. The
stem of the Convolvulus, looked at from above, twines from
right to left (contra-clockwise). Most twining plants twine
in the same direction ; that of the Black Bryony, however,
twines from left to right (clockwise). By this means such
plants are able to climb many feet above ground, and to
reach the air and sunlight without the expenditure of
energy required in building up strong erect stems.

Climbing organs sensitive to contact. Tendrils. — In the
White Bryony (Bryonia dioic a) (Fig. 91), Clematis (Fig. 92),
Bush Vetch (Fig. 220), and Sweet-Pea (Fig. 131), slender
climbing organs called tendrils are developed, which differ
from climbing stems in being sensitive to contact.

The Passion Flower has very sensitive branch-tendrils
whose movements are easily observed. Fig. 93 shows the
result of an experiment with one such tendril. At 3.10 p.m.
the concave side of the tendril was gently stroked with
a slender stick and records of its 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 spiral
should be produced can be easily understood if you fix
a piece of string at both ends and turn the middle portion :
the part on the right turns in the opposite direction to
that on the left. Tendrils showing the reversed spiral are
also seen in the White Bryony (Fig. 91). The tendrils of
the Virginia Creeper (Fig. 94), 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 with
a rough surface, become coated with mucilage and are
thus cemented to the support.

Tendrils are sensitive thread-like plant organs by which

a
u

«J

m
><

ffl

O
2

0!
Q

w
H

W
►J

« w

rh H

W
H

(/I

w
>

o o

144

MOVEMENTS AND ATTITUDES OF PLANTS 145

Fig. 92. Leaf-stalk
Tendrils of Clematis.

---.

s »
« 1

S10

Fig. 94. Branch of Vir-
ginia Creeper. — t, branch-
tendrils with adhesive disks ;
the shoot shows transitions
from simple to compound
palmate leaves.

Fig. 93. Movements
of the Branch-ten-
drils of the Passion
Flower.

1296

146

THE VEGETATIVE ORGANS

Fig. 95. Shoots of Gooseberry. — i, position of leaves in the
shade ; 2, in the sunlight ; p. leaf-base prickles.

MOVEMENTS AND ATTITUDES OF PLANTS 147

a plant fixes itself to a support. They may be modifica-
tions of (1) branches, e. g. Passion Flower, Vine, Virginia
Creeper, and White 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 positions. — If you note the differences of
position of leaves in sunny places and compare these leaves
with others of the same kind growing in the shade, you will
see that they take up a favourable position with reference
to light. Fig. 95 shows two shoots of Gooseberry taken
from different sides of the same plant. One (1) was over-
shadowed by branches of an apple-tree, and exposed its
leaves fully to the available light. The other (2) was not
overshadowed, and its leaves moved in such a way as to
expose the edges of their blades to the direction of the sun's
rays. As chlorophyll 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 rays
of the sun.

Fixed light position. — Some Acacias (Fig. 96, 1) growing
in sunny regions have curiously modified leaves, which
persistently turn their edges to the sky and give a char-
acteristic 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 attitude assumed
by the foliage of a plant with reference to light is called
the ' fixed light position '. In some plants the leaves are
reduced to scales, the stems flatten out, resemble leaves,
and, as in the Acacias, turn their 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
(Myrsiphyllum) (Fig. 96, 2) and species of Asparagus.
Extraordinary 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-

K 2

148

THE VEGETATIVE ORGANS

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 is a

Fig. 96. Stems which perform the Functions of Leaves. —
1, Acacia ; 2, Smilax ; 3, Cactus ; l.s, leaf-spines ; r, leaf-like
petioles (phyllodes) ; Pc, leaf-like stem (phylloclade) ; s.l, scale-
leaf.

tendency for plants growing in dry and very sunny places
to take on strange shapes and exhibit curious devices which
help the plant to survive under trying conditions.

Protective movements against radiation and transpiration. —
Movements which have for their object reduced radiation
and transpiration are also very common. Note how young
leaves emerge from the buds in spring in, e.g., the Elm
(see Fig. 198, 1), Beech (see Figs. 75 and 76), Lime, and
Horse-Chestnut (see Fig. 68). At first they are erect, then
as they unfold and grow they bend over and hang down-
wards with their under surfaces applied one to another so

MOVEMENTS AND ATTITUDES OF PLANTS 149

as to expose a relatively small area to the cold and drying
winds. As they expand and grow larger and stronger
they assume a favourable position with regard to air and
sunlight and form a mosaic.

Motile organs of hedgerow plants. — Examine the trees and
shrubs in a wood or hedgerow and note how frequently the
blades face the light. What part has moved to bring them
into this favourable position? Privet, Yew (Fig. 97), Ivy
(Fig. 222, i), White Bryony (Fig. 91),
Convolvulus (Fig. 89), Elm, Syca-
more, and many other examples
will be found. The bases of such
leaves are swollen, and it is this
cushion which is usually the organ
of movement. Sometimes there is
a motile organ at the upper end
of the leaf-stalk near the blade.
In other cases the cushions become
highly specialized organs, and the
leaves, and even the leaflets, are
able to execute periodic, and some-
times rapid, movements. Obser-
vations should be made on a few

common plants, such as the White Clover and Wood
Sorrel.

Sleep-movements in Clover, Wood Sorrel, and False Acacia.
—The Clover leaf (Fig. 98) is borne on a long stalk with
a cushion at the base, covered by a pair of stipules. During
the day the blade at the end is horizontal and divided into
three leaflets (trifoliate). A slight variation in the form of
the cushion will cause much movement of the blade at the
end of its long lever. Similar cushions are found at the
base of each leaflet, and at dusk, by their aid, the two side
leaflets move into a vertical position, exposing their inner
edges to the sky and their outer edges to the ground. The

Fig. 97. Branch of
Yew. — Leaves arise spi-
rally on the axis, but the
blades turn to the light.

i5o

THE VEGETATIVE ORGANS

middle leaflet now bends over them, folding the two sides
of the blade downwards and exposing the back of its midrib
to the sky. The amount of leaf-surface exposed to radia-
tion is thereby greatly reduced, and in keeping with this,
the lower and more exposed leaf-surfaces contain fewer
stomata than the upper and more protected ones. During
the 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 Wood Sorrel

Fig. 98. White Clover. — 1, trifoliate leaf, day -position ; 2,
night -position ; in, motile organs ; 3, 4, and 5, inflorescences of
Clover : the flowers turn downwards after pollination.

(Fig. 99) or a common garden Oxalis. In these plants the
three leaflets droop at night, hang vertically, apply their
midribs to each other, and so expose their upper and
protect their under surfaces, to which the stomata arc
restricted. They thus secure protection against cold, but
by 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 habit 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 sleep-movements.

The False Acacia (Robinia) furnishes another example
of motion in plants, and its leaf-movements should be

MOVEMENTS AND ATTITUDES OF PLANTS 151

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 of leaflets ; c, night-position ; d, bases of leaflets
enlarged ; e, f, g, movements of growing flower-stalk ; h, bulbils
in the axils of leaves ; *, vertical section of a bulbil ; m, motile
organs ; r, rhizome.

A leaf of the False Acacia, like 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,

152 THE VEGETATIVE ORGANS

apply their upper surfaces each to the opposite one, and
point their tips to the sky. At night they droop and apply
their under surfaces together. Thus they obtain the
advantages of favourable light, escape the injurious effect
of intense light, and, on assuming the night-position, reduce
the loss of heat from radiation.

Rapid movements in Sensitive Plants. — Some plants exhibit
the power of movement to such a degree as to have earned
the name of Sensitive Plants. The most familiar example
is Mimosa pudica, the Sensitive Plant. Its leaves are
bipinnate, i. e. each leaflet or pinna is again pinnately
divided into similar segments or pinnules. The end of each
leaflet has a pair of pinnules. At the base of each leaflet
and pinnule, and also at the base of the leaf-stalk, there is
an organ of movement, and the leaves exhibit sleep-move-
ments such as are seen in the Clover and Wood Sorrel.
So sensitive are the leaves, that a very slight stimulus
causes the leaflets to droop in the daytime. If a lighted
match be held under the end of a leaf, the heat-stimulus
produces a series of remarkable changes. Not only do the
heated pinnules droop, but the stimulus is transmitted
from one to another, pinnules and leaflets drooping in
succession, until, eventually, the stimulus reaching the
cushion on the leaf-base, the whole leaf hangs down lan-
guidly. There it remains until the shock has passed off,
when it gradually regains its former position. The leaves
of the Venus' Flytrap close up in a similar manner, but very
rapidly, in response to a contact-stimulus (see p. 366).

These movements are due to rapid changes in the tur-
gidity 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 air-spaces. Later, as the
cells once more become turgid, the leaves and leaflets resume
their ' awake ' position.

Movements of flowers and fruits. — Flower-movements

MOVEMENTS AND ATTITUDES OF PLANTS 153

are equally interesting and easy to observe. Sleep-
movements are common and, in different species, occur
at different times of the day and night. Usually flowers
pollinated by day-flying insects are open by day and closed
at night, while flowers visited by night-flying moths are
open in the evening or at night, when they are often sweet-
scented, and are white or pale yellow in colour. Some
plants owe their common names to their habit of opening

Fig. 100. Evening Primrose, showing the Movements of the
Parts as the Flower opens.

and closing their flowers, e.g. the Daisy (day's-eye), John-
go-to-bed-at-noon, and Poor Man's Weather-glass. These
movements are related either to the habits of the insect-
pollinators, or to weather-changes, many flowers closing
during cold, dull, or wet weather, and so protect their honey
and pollen.

The opening of some flower-buds occurs so quickly as
to be easily observable. It is quite exciting to watch the

154 THE VEGETATIVE ORGANS

flowers of the Evening Primrose as they open on a warm

summer's evening. Fig. ioo shows the stages observed

in two flowers. The calyx slips down on one side and the

four free tips curve back and reveal the rolled-up petals.

The corolla unscrews at the base, causes the calyx to split

more and more, and as the petals unroll, the mouth of the

corolla opens and the stigmas appear. The calyx now

splits at the bottom, the sepals suddenly turn backward,

or inside out, with a distinctly audible click, and the

crinkled petals unroll, slide over one another, and soon fully

expand. The sound produced resembles that of two sheets

of paper, one gliding over the other. If we look at the

stamens we find that the stringy pollen is already hanging

out of the anthers, while the stigmas, not yet ripe, spread

out their four lobes well above them. As many as a dozen

flowers may be seen to open in this way on one plant in

half an hour.

The various attitudes that flowers assume should be

carefully observed under the following conditions : (i) in

bud, (2) in flower, (3) in sunshine, (4) in cloudy and wet

weather, (5) during the day, (6) at night, (7) as the fruit

ripens, and (8) when the fruit is ripe. Figs. 101 and 102

show the movements of the flowers and fruits of the Wild

Hyacinth. Notice that the flowers are erect in bud ; later

they turn away from the axis, expand and hang downwards,

the lowest and oldest opening first. After pollination they

become erect again, while the fruit-stalk lengthens and

becomes rigid. In the White Clover (see Fig. 98), the

flowers are erect in bud, horizontal in flower, and after

fertilization hang downwards. The Wood 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. 103 shows the movements of the parts in an opening
inflorescence-bud of the Horse-Chestnut.

Fig. ioi. Flower-movements of Wild Hyacinth.

,>4 %» ii, 4

Fig. 102. Fruit-movements of Wild Hyacinth.

'54

Fig. 103. Three Stages in the opening of the Terminal
Inflorescence Bud of Horse-Chestnut.

'■^\Jfa'-- * <% ^ '..'

. t^n^

\ \ -. . » » » ;

■• . : >-. -jr"X^ .-, • <••*.»■• V.\

Fig. 104. Dandelion. — The stalks of the open flower-heads
are erect ; after pollination the heads close up and the stalk bends
over to the ground.

'St

MOVEMENTS AND ATTITUDES OF PLANTS 155

The movements of the flowers and flower-stalks of
Poppies, Columbines, and Bellflowers {Campanula) should
be compared and their differences noted.

In some cases the whole inflorescence is involved in the
movements, e. g. in the Dandelion it is erect in bud, and
when the flowers are open (Fig. 104) ; at night and in wet
weather the flowers close and are protected by the inner
whorl of bracts. After pollination the stalk grows, bends
over and lies almost prostrate, becoming erect again as the
fruits ripen. At this stage the disk enlarges and becomes
convex, the bracts turn backwards against the stalk, the
pappus-hairs spread outwards and the fruits are ready for
dispersal by the wind. In the Coltsfoot the stalk is erect
in the bud and in the flowering stages. After pollination
the upper part bends over, bringing the head into a drooping
position, and the fruits, protected from the rain, complete
their development. As they ripen, the stalk elongates,
becomes erect and rigid, and raises the fruits into a favour-
able position for dispersal.

The power of movement in plants is an important aid
to protection. By this means, during suitable sunlight,
leaves are placed in the most favourable position for
photosynthesis ; during intense light, the adoption of the
edgewise position protects the chlorophyll against decom-
position ; leaves and leaflets applied to one another reduce
the exposed surface and check loss of water by transpiration
and loss of heat by radiation. Flower-movements protect
the honey and pollen from rain and from useless insects,
and finally the fruits when ripe are moved into the most
favourable position for seed-dispersal.

PART II

THE REPRODUCTIVE ORGANS

CHAPTER XII

BIOLOGY OF THE FLOWER. DICOTYLEDONS

I. Pollination of Simple Flowers by Wind 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 elongating, remain un-
developed ; and that, in consequence, a number of leaves
spring close together from the short axis. Some of the
leaves arise singly and are arranged in a close spiral, while
others stand two at a level, in crossed pairs.

The flower a condensed and modified shoot. — In our exam-
ination of the Stock flower we found something very similar,
viz. a condensed or dwarf shoot, with a tendency for the
flower-leaves to arise close together in crossed pairs. This
condensation is characteristic of flowers, and it is interesting
to note how frequently flowers arise on dwarf, leafy shoots,
or spurs, as in many fruit-trees. This shortening of the
axis, together with the great modification that has taken
place in the size, shape, colour, and function of its parts,
distinguishes a typical flower from any other part of the
plant.

Flowers, however, have not arisen in this simple way
from a leafy shoot. It is more probable that stamens and

BIOLOGY OF THE FLOWER

157

carpels, or their equivalents, came into existence first, and
that petals, and perhaps sepals, were derived from them
by modification of their parts, as may be seen in double
flowers like roses, and in the White Water-Lily (Fig. 105).
Very ancient flowers had many 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.
Generally the flowers appear towards the end of a season's
activities. In an annual they herald the closing scenes of
its life-cycle and provide for the formation of fruits and
seeds, which will soon be all that remain to perpetuate the
race. In some cases flowers appear early in the season and

Fig. 105. Stamens of Water-Lily, showing transition
from Stamens to Petals.

before the leaves, as in many trees, and in the Coltsfoot,
Wood Anemone, and many other herbs. In the Autumn
Crocus, or Meadow Saffron (Colchicum autumnale), on the
other hand, the leaves complete their work and die down
before the flowers appear. Whether early or late, however,
the chief object of the flower is to produce fruits containing
seeds, which, on falling to the ground, may produce a new
generation ; and all the parts of a flowerdirectly or indirectly
serve this end.

Structure and functions of the parts of a flower. — The four
parts of a typical flower are usually arranged in successive
whorls on the short axis, which is known as the receptacle.
The lowest and outermost is composed of small green sepals

158

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 honey-secreting glands. In
consequence of their colour, scent, and honey, they are
attractive to insects. The two inner whorls differ 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 sporophylls
lying immediately within the corolla is the androecium,
and consists of small-stalked bodies, the stamens. Each

Fig. 106. Transverse Sections of Anthers.
i, before; 2, after dehiscence; Po, pollen-grains.

stamen has a slender stalk or filament, bearing on its free
end the anther ; this consists of four parallel pollen-sacs
(Fig. 106), or microsporangia (Gr. mikros = small, spora
— a seed, angeion = a case), within which are a large number
of pollen-grains or spores (Po), whose production is the
special function of the stamen. These minute spores are
called microspores, and the organ which bears them (the
stamen) is the microsporophyll (Gr. phyllon = a leaf).
In some flowers the stamens are attractive 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 constitute
the gynoecium, or pistil. Usually three parts of the

BIOLOGY OF THE FLOWER 159

pistil may be distinguished : (1) the ovary, within which
the ovules are developed ; (2) the style, growing from the
top of the ovary and ending in (3), a stigma which, when
ripe, is coated with a sticky sugary secretion. To this the
pollen-grains adhere and germinate. The ovules, after
fertilization by the pollen, undergo changes which result
in the formation of seeds. Each ovule or megasporangium
(Gr. megas = large) contains a megaspore (the embryo
sac), and the sporophylls which bear them are known as
megasporophylls.

The essential work of the flower is to secure the trans-
mission of pollen-grains from the stamens to the stigmas,
a process known as pollination, so that fertilization of the
ovules may occur and seeds be formed. The flowers of
different plants vary considerably in structure according
to the way in which pollen is conveyed. It may be carried
by the wind or by insects, or the arrangement and be-
haviour of the parts may be such as to transfer pollen from
the anthers to the stigmas of the same flower. If we
examine a number of common flowers from this point of
view, we shall learn much of their structure and modifica-
tions, and also of their special use to the plant. Each
flower should be carefully examined, and floral diagrams
and drawings made to show the relationships of the parts,
especially as seen in a vertical section.

Flowers pollinated through the agency of wind. — The
flowers of the Hazel or Oak (Figs. 187 and 194) are arranged
in a catkin. Each flower of the long yellow catkin is much
smaller than that of the Stock ; outside are five or seven
green scales ; within are five to twelve stamens, but no
pistil and no corolla are present. The flowers in the smaller
bud-like catkins have six small scales on the top of an
ovary with three chambers, and there are three large sticky
stigmas to catch the pollen. From these flowers both
stamens and corolla are absent.

160 THE REPRODUCTIVE ORGANS

Many of our forest trees produce similarly reduced flowers.
This arrangement, in which the stamens and the pistils are
in different flowers but on the same tree, is called monoe-
cious (Gr. monos = one, oikos = a house). Such flowers
are inconspicuous and unscented, and the staminate
flowers produce a large quantity of pollen which is loose,
dry, and light, and easily carried by the wind to the large
stigmas of the pistillate flowers. In the Willows (Fig. 185)
and Poplars (Fig. 186) the two kinds of catkins are borne
on different trees, and this arrangement is called dioecious
(Gr. di = two). In all such cases the pollen carried to the

stigma comes from another flower,
and when this occurs the flower
is said to be cross-pollinated. In
Willows the stamens are bright
yellow and numerous, and each
flower contains a honey-gland or
nectary at the base. Insects often
visit these catkins and collect from

Fig. 107. Ripe Stigmas 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 it deposited on the stigmas.

From the abundance of fruits produced by such trees
it is obvious that simple and unattractive as the flowers
are, they yet contain all that is essential for fruit-produc-
tion. Hence stamens and pistil are spoken of as the
essential organs of the flower. In the flower of the Stock
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.

Self-pollinated flowers. — In the flower of the Round-
leaved Mallow (Fig. 107) there are five free sepals and

BIOLOGY OF THE FLOWER

161

five free petals ; the stamens are numerous, but their
filaments are all joined to form a tube round the pistil,
hence called monadelphous (Gr. adelphos = brother). The
pistil is superior, the carpels numerous and syncarpous.
There are many long stigmas which, if not cross-pollinated,
grow, curl over among the anthers, and thus receive pollen

Fig. 108. Modifications in the Mouth-parts and Legs of
Insects which collect Honey and Pollen from Flowers. —
Po, pollen grains (after Sharp and Muller).

from the same flower. By this means self-pollination takes
place.

Flowers attractive to, and pollinated by, insects. — Flowers
which develop bright colours, scent, or honey, attract large
numbers of insects, which feed on the honey and pollen ;

1290 r

162 THE REPRODUCTIVE ORGANS

and many of the modifications found in flowers are paral-
leled by modifications of the mouth-parts of insects
(Fig. 108). The mouth-parts of the simpler insects, e. g.
beetles and flies, are so short that they are unable to reach
the honey unless it is exposed in an open, shallow flower.
Honey in a deep tube is inaccessible to them, and only
insects with mouth-parts elongated to form a proboscis are
able to reach it. Some flowers have tubes several inches
long (8 to 10 inches), and there are insects with probosces
long enough to obtain honey from the bottom of them.

Insect pollinators and their month-parts. — Fig. 108 shows
the mouth-parts of various insects which visit flowers,
i is the head of a beetle (Strangalia attenuata) which can
lick honey from shallow flowers ; 2, the head of the Drone
Fly (Eristalis 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 pilipes) ; 6, the end of the
proboscis enlarged to show the ' honey-spoon ' ; 7, the
Honey Bee (Apis mellifica) with masses of pollen (Po) on
the hind legs ; 8, the hind leg of a bee with mass of pollen ;
9, collecting-hairs on the leg of a Honey Bee ; 10, a hair
magnified, with pollen-grains attached; 11, proboscis of
a moth, which is very long and coiled up like 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 has
probably been an important factor in the evolution of many
flowers. On the other hand, the insects have themselves
become modified, especially in the organs surrounding the
mouth.

Insects, useful and injurious. — In the mature stage, insects are
often very useful to flowers, and in many cases seeds can only
be developed when insects act as pollinators. It is during this

BIOLOGY OF THE FLOWER 163

stage in their life-cycle that insects lay their eggs. In time the
eggs are hatched, and the very small grubs or caterpillars have
to search for food with which to complete their development.
As they are mostly vegetable feeders, the caterpillars or larvae,
especially of moths and butterflies, do much damage to plants ;
and, if they are abundant, may strip a whole forest of its leaves
in a short time. Garden and field crops often suffer greatly from
this cause, resulting in a loss of many thousands of pounds.

Insects of many kinds, either in their larval or adult stage, are
destructive to plants, both wild and cultivated. On the other
hand, some are useful. Among the more destructive are :

Injurious insects. — (1) The small Aphides or Plant Lice, and Scale
Insects (Hemiptera), which make great ravages in both garden
and field.

(2) The larvae of butterflies and moths (Lepidoptera), e.g. the
Cabbage White Butterfly, the Cabbage Moth, Magpie Moth, and
Antler Moth, which injure field and garden crops. The Lackey
Moth, Buff-tip, Vapourer Moth, Ermine Moth, and several Tor-
trices affect fruit and forest trees.

(3) The larvae of many flies (Diptera), such as the Wheat
Midge, Gout Fly, Daddy-long-legs or Crane Fly, Cabbage Fly,
Radish Fly, Mangold Fly, Onion Fly, and Root Fly are pests on
roots and other crops.

(4) Larvae and mature beetles (Coleoptera) , especially the Mustard
Beetle and many Weevils.

(5) Many Hymenoptera, such as the Gooseberry Saw-fly, Pine
Saw-fly, Turnip Saw-fly, and Corn Saw-fly, are often very destructive
to both herbaceous and woody plants.

Fortunately for man, these pests are the chief source of food for
certain animals, and are thus kept in check. Such birds as the Fly-
Catcher, Wagtail, Tits, Wren, Hedge-Sparrow, Swallow, and others,
eat insects in enormous numbers. The Lady-bird Beetles, both larvae
and mature beetles, live on Aphides, Scale Insects, Mites, and other
pests, and are invaluable friends of the farmer and gardener. The
larvae of Ichneumon flies live as parasites within the bodies of
many plant-eating insects, and so destroy large numbers. It is
thus important that nature's balance should not be interfered
with. Man often destroys useful animals, and in consequence
suffers from the depredations of pests which these animals would
naturally keep in check.

As botanists, our chief interest in insects is as pollinators
of flowers, and we will examine a number of common forms

l 2

ifH THE REPRODUCTIVE ORGANS

of flowers to determine the chief devices for securing pol-
lination and the part played by insects in bringing it about.

Pollen- flowers : simple forms visited by insects for pollen.
— The Clematis or Traveller's Joy (Fig. 109) has a calyx
consisting of four greenish-white sepals which resemble
petals, hence said to be petaloid. There is no corolla ;
the stamens are numerous and arranged below the pistil,
not in whorls, but spirally. The pistil consists of many
carpels which are free from one another, and are hence
said to be apocarpous (Gr. apo = from). The flowers
secrete no honey, though they provide much pollen for
their insect visitors.

In the Wood Anemone (Fig. no) the flowers appear
before the leaves ; but below the flower is a whorl of three
large green, leafy bracts. The calyx consists of five peta-
loid sepals which are pinkish-white and conspicuous, and
act as petals, the corolla being absent. The stamens
are numerous (indefinite), and arranged spirally below the
pistil, which consists of many small, spirally arranged
carpels, free from one another. Examine flowers of different
ages, and notice the order of ripening of the stamens and
carpels. The outer stamens open first, the stigmas being
covered by the inner ones. There is no honey in the flower,
but it is visited for pollen by insects which alight in the
centre, 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. in) is a similar flower with
a large attractive calyx of five or more yellow sepals. The
stamens are numerous and open outwards ; the carpels are
free, and each contains several ovules. On the sides of each
carpel and near the base are two shallow depressions where
honey is secreted. This is an additional attraction for
insects. Notice the curious stipule (st), which is quite

Fig. 109. Flowering Shoot of Traveller's Joy.

164

BIOLOGY OF THE FLOWER

165

Fig. ho. Wood Anemone. — br, bract ; ca, calyx ;
/, foliage-leaf; r, rhizome.

i66

THE REPRODUCTIVE ORGANS

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. 112) has five free sepals (poly-
sepalous), and alternating with them are five free petals

Fig. in. Marsh Marigold. — ca, calyx ; si, stipule.

(polypetalous). Examine the bases of these and note the
honey-glands. The stamens are numerous (indefinite),
and arranged spirally below the pistil ; they ripen before
the carpels, and in succession from without inwards.
The lower stamens first turn outwards and conceal the

BIOLOGY OF THE FLOWER

167

Fig. 112. 1, Tuberous Buttercup; 2, petal .removed; 3,
vertical section of flower ; a, stamen ; by, bract ; c, carpel ; ca,
reflexed sepal ; n, nectary ; p, petal ; r, receptacle ; t, tuber.

i68

THE REPRODUCTIVE ORGANS

nectaries 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, each
containing 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 below the pistil, are said to be hypogynous.
The Buttercup provides both pollen and honey, but in
order to obtain the latter, insects must first push aside the

-P

Fig. 113. Flower of Strawberry. — 1, back of flower, showing
the five sepals (ca) and five smaller stipules (st) alternating with
the sepals ; 2, flower in vertical section ; a, stamen ; c, carpel ;
ca, sepal ; g, upgrowth from centre of receptacle bearing the carpels ;
p, petal ; r, expanded and hollowed receptacle ; st, stipule.

stamens, and in doing so their bodies become dusted with
pollen. If they now visit older flowers where the stigmas
are ripe, they may deposit on them some of this pollen.
The different kinds of buttercups should be examined and
their differences observed.

Perigynous and epigynous flowers ; the simple flower -tube.
—The Strawberry (Fig. 113) has five sepals and five
sepal-like stipules, the latter forming what is called an
epicalyx. The flower thus appears to have ten sepals.
These, together with the five alternating petals and numer-
ous stamens, are borne on the edge of an expanded and

BIOLOGY OF THE FLOWER

lb <j

slightly hollowed receptacle, at the base of which is a fleshy,
ring-like nectary. From the centre is an upgrowth from
the receptacle, upon which are the numerous carpels. The
stigmas ripen before the anthers, and thus cross-pollination

Fig. 114. i, Flowering Shoot of Rose; 2, vertical section
of flower ; a, stamen ; c, carpel ; ca, sepal ; p, petal ; Pr, prickle ;
r, receptacle ; st, stipule.

is favoured. Flowers which thus bear their sepals, petals,
and stamens on the edge of a cup-like receptacle, and there-
fore around the pistil, are said to be perigynous. The
flower of the Strawberry should be carefully compared with
that of the Buttercup.

170

THE REPRODUCTIVE ORGANS

In the Rose (Fig. 114) the receptacle is hollowed deeper
still, and arising from the edge of it are five reflexed sepals,
five petals, and numerous stamens, all of which are peri-
gynous. Within the cup and fixed to the sides are several
free carpels, each containing one ovule. No honey is
secreted, but the stamens provide much pollen for insects.
The Rose and Clematis are therefore called pollen-
flowers.

The flowers of the Cherry (Fig. 115) and Plum have
a receptacle which is hollowed, and on its edge are five
sepals, five petals, and numerous stamens (i. e. they are

Fig. 115.

Vertical Section,

Flower of Cherry.

Fig. 116.
Vertical Section,
Flower of Apple.

perigynous). There is only one carpel, and this is superior
to and free from the receptacle-cup. The anthers and the
stigma 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 is
secreted by the receptacle-cup, and insects collecting honey
and pollen may touch the stigma with pollen brought from
another flower, and thus bring about cross-pollination ; but,
owing to the relative position of the anthers and stigma,
self-pollination will very commonly occur. The whole of
the fruit is formed from the carpel ; the receptacle-cup
is thrown off and does not form part of the fruit.

BIOLOGY OF THE FLOWER 171

In the Apple (Fig. 116) and Pear the pistil consists of
five 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 honey
is 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-pollination. If insect-visits
fail, pollen may be shaken or may fall on to the stigmas ; this
is aided by the horizontal position of the flowers. After
fertilization the receptacle enlarges and forms the fleshy
part of the fruit. The five united carpels form the core

(Fig- I5S).
Examine old fertilized flowers of the Strawberry, Rose.

Cherry, and Apple, and note in each case the mode of origin

of the fruit and the structures concerned in their formation.

Tubular flowers with concealed honey. Devices to secure
cross-pollination. — In the Stock (Fig. 3, 1) the four upright
sepals form a narrow but split tube, which conceals the
nectaries 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 more
intelligent and better adapted for carrying pollen from
anther to stigma than the short-tongued insects, like beetles
and flies, which may take pollen and honey from shallower
flowers with less likelihood of bringing about pollination.

Those flowers, therefore, which attract the more intelli-
gent insects possess a double advantage : (1) they need
less pollen, and (2) cross-pollination is more certain. Let
us see by what means these advantages are secured in
some other flowers.

172

THE REPRODUCTIVE ORGANS

In the Geranium the calyx has five sepals joined by
their edges to form a deep tube. A united calyx is said to
be gamosepalous (Gr. gamos = union). The five petals
are free ; there are ten stamens, five outer and five inner.
At the bases of the five outer ones are nectaries. It is
interesting to watch the movements of the stamens in the
Field Geranium. When the flower opens, the stamens lie
on the petals ; they then raise themselves parallel to the
pistil, shed their pollen, and return — first the outer set, then
the inner — to their former position. The pistil consists

Fig. 117. 1, Flower of
Garden Geranium ; 2, trans-
verse section of pedicel and
nectary ; n, nectary ; p, pedicel
of flower.

Fig. 118. Flower of Gar-
den Nasturtium. — n, honey-
secreting spur ; p, pedicel.

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
pistil are said to be proterandrous.

Compare with this the Garden Geranium (Pelargonium)
(Fig. 117). 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 different times. Look for the long tubular
nectary which adheres throughout its whole length to the
flower-stalk. The presence of the nectary in the Pelar-

BIOLOGY OF THE FLOWER

173

gonium destroys the symmetry of the flower. In the
previous examples the flower can be divided into more
than two similar halves. Such flowers are said to be
regular, or actinomorphic (Gr. aktis — a ray, morphe =
shape). The Pelargonium, however, can be divided into
only two similar halves, and hence is said to be irregular or
zygomorphic (Gr. zygos = a yoke).

The Garden Nasturtium should also be examined
(Fig. 118). Note the long spur, which is a hollow out-
growth of the floral axis and contains the honey. The
calyx, as well as the corolla, is coloured, and the fringes on

Fig. 119. 1, Flower of Chervil ; 2, vertical section
of flower ; d, disk ; 0, inferior ovary.

the three lower petals serve to keep rain out of the honey-
tube. Watch the stamens as they ripen, and note how
each in turn bends upwards in front of the entrance to the
tube and ripens so that it will be touched by a bee visiting
the flower. The}' then bend down out of the way, and
later the stigma assumes the position previously occupied
by the stamens, and is thus likely to become cross-pollinated.
The flower of the Chervil, or Beaked Parsley (Fig. 119),
shows several important differences. The flowers are small
and crowded together in a flat-topped inflorescence, called
a compound umbel (L. unibella = a sunshade). The calyx
consists of five minute sepals, and alternating with them
are five petals of different sizes ; the outer and anterior
one is the largest ; then follow two intermediate ones ;

174 THE REPRODUCTIVE ORGANS

lastly the two inner ones, which are the smallest. Alter-
nating with these are five stamens, which shed their pollen
before the stigma is ripe. These three whorls, unlike the
preceding examples, spring from the top of the ovary,
and hence are said to be epigynous. The pistil consists
of two united carpels inferior to the other whorls. On
the top of the ovary is a honey-secreting disk (d), which
surrounds the two stigmas, and these ripen only when the
pollen of the same flower has been shed. The honey is
freely exposed and liable to be spoiled by the rain, and
may be obtained by short -tongued insects which commonly
visit the flowers. In this case conspicuousness is due to
the aggregation of many small flowers at the same level in
the inflorescence, and by the outer petals enlarging at the
expense of the inner ones.

The Buttercup, Stock, Strawberry, Rose, Geranium, and
Chervil all agree in one important respect — their petals are
not joined, i.e. the corollas are polypetalous. In most
cases the sepals also are free. In the Geranium, however,
they are united, and the calyx is gamosepalous. These
flowers also show different methods of forming the flower-
tube, namely : (a) by erect sepals, as in the Stock ; (b) by
a hollow receptacle, as in the Strawberry and the Rose ; and
(c) by united sepals, as in the Geranium.

CHAPTER XIII

BIOLOGY OF THE FLOWER {Continued)

II. Pollination of Tubular and Highly Developed Flowers

The flowers we have considered above are generally
simple in structure. Flowers pollinated by the wind have
no perianth, or only a very rudimentary one ; they are
small and inconspicuous, and produce much pollen ; and
the stigmas are large, branched and sticky, to catch the

BIOLOGY OF THE FLOWER

175

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 usually attractive. In the
lower types the parts are free, the flower-cup is more or
less open, and the pollen and honey are very accessible
to insects. In vaiious ways, however, a flower-tube is
developed in higher forms which protects the honey
from rain and excludes the lower types of short-tongued
insects.

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.

Tubular flowers with united petals.
— The Cross-leaved Heath has five
united sepals and five petals joined
by their edges to form a tube ;
the corolla is thus gamosepalous.
Within the bell-shaped corolla (Fig.
120) are the stamens, which are

peculiar. Each anther has two long processes or arms,
and these project outwards towards the corolla- wall. Near
the top of each anther are two pores, through which the
pollen escapes when ripe. The pistil is superior and
syncarpous, and around its base is a ring-like nectary ;
the style is long and projects beyond the anthers to the
mouth of the bell. An insect visiting the flower will
bring its head against the stigma 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. 120. Flower of
Cross-leaved Heath. —
Pr, anther-processes ; st,
stigma.

176

THE REPRODUCTIVE ORGANS

short-tongued insects : the chief visitors are bees, lepi-
doptera, and long-tongued flies. The flowers of the Heaths
hang downwards, so that the honey is protected from
the rain.

Different kinds of flowers in the same species. — In the
Primrose (Fig. 121,1) and Cowslip (Fig. 121,2) the five united

Fig. 121. i, The Primrose; 2, Cowslip; 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-like
stigma at the mouth of the tube and the anthers half-way
down (Fig. 121, 3), and the other with the five stamens at the
mouth of the tube and the stigma half-way down (Fig. 121, 4) .

BIOLOGY OF THE FLOWER 177

The long-styled form is known as ' pin-eyed ', and the
short-styled form as ' thrum-eyed '.

Species which thus produce two kinds of flowers are said
to be dimorphic. (The Loosestrife has three kinds of
flowers, and hence is trimorphic.)

The pistil of the Primrose consists of five carpels, superior
and syncarpous, but it differs from the previous examples
in that the numerous ovules are borne on placentas on
a central column, which is free from the ovary-wall, and
such an arrangement of ovules in an ovary is called ' free-
central placentation ' (Fig. 121, 3 and 4). Round the base
of the ovary, honey is secreted, and an insect visiting these
two kinds of flowers will receive pollen on its proboscis at
two different points : at its base will be the larger pollen-
grains of the short-styled form, and in the middle of it the
smaller pollen-grains of the pin-eyed form. Thus pollen-
grains of one form are likely to be transferred to the stigma
of the other form. Here, as in the Heaths, Stock, and other
plants, self-pollination may occur by pollen-grains falling
on to the stigma of the same flower.

If a Primrose plant is covered with a bag to exclude
insects, and its flowers compared later with uncovered ones,
the latter will be found to produce more ripe seeds than the
former. It was by similar experiments that Darwin and
others showed how important insects are, as pollinators
of flowers.

Small flowers massed in heads. — The Daisy (Fig. 122)
shows specialization similar to that already noticed in the
Chervil, where small flowers, inconspicuous in themselves,
are rendered attractive by being massed together in a con-
densed inflorescence. In the Daisy and its allies this has
reached the highest stage of development ; condensation
has occurred to such an extent that the whole inflorescence
has the appearance of a single flower. Such a head of
florets (Fig. 64) is called a capitulum.

1296 M

178

THE REPRODUCTIVE ORGANS

Outside is a series of small bracts resembling a calyx
and known as the involucre. 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 small strap-
shaped flowers are called ray-florets
(Fig. 122, 1). The yellow disk in the
centre is composed of florets of a
very different type (2). The pistil, as
in the ray-florets, has an inferior
ovary of two carpels ; there is no
calyx ; 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. Such
united anthers are said to be
syngenesious (3). These are known
as disk-florets.

If the disk-florets in the head of
a Daisy are examined, it will be
seen that the outer (lower) florets
are the older, and are the first to
open. The following stages should be looked for : (1) the
style is short and within the anther-tube (when ripe the
anthers shed their pollen into the tube and on the top
of the stigma, which has two lobes, the outer face of
each being provided with a brush of hairs) ; (2) later, the
style elongates, and the stigmatic brush sweeps the pollen

OV.

Fig. 122. Florets of
Daisy. — 1, ligulate, fe-
male ray-floret; 2, tubu-
lar, hermaphrodite disk-
floret ; 3, stamens with
united anthers ; ov, in-
ferior ovary; p, corolla.

BIOLOGY OF THE FLOWER 179

out of the tube ; (3) the stigma-lobes then open, throw-
ing the pollen off, and exposing their 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 cross-
pollination of two degrees is possible : (1) a cross between
two florets of the same head, and (2) a cross between florets
on different Daisies. Honey, which is secreted by a ring-
like nectary round the base of 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 narrow
tubes; (3) accessibility of pollen and honey to a great
variety of insect visitors ; (4) pollen presented so as to
secure cross-pollination in the case of insect-visits, or self-
pollination in their absence.

The Coltsfoot. — The bright yellow flower-heads of the
Coltsfoot 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 which 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 small, very hairy
bracts, 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 the
flat disk ; determine the different kinds of florets in the
head, and the interesting division of labour they show
(Fig. 123).

The outer, strap-shaped florets are the most numerous

m 2

i8o

THE REPRODUCTIVE ORGANS

(about three hundred). Each has an inferior ovary, and
above it is the calyx, consisting of a whorl of hairs. Such
a calyx is said to be pappose. Within this is the ligulate
corolla. The style has a two-lobed stigma, and also a brush
of hairs, which, however, is of no use, as these florets have
no stamens, i. e. they are all pistillate ; no honey is secreted,
and they are ripe before the inner florets. About forty
tubular flowers will be found in the centre, differing
from the outer ones as follows: they are smaller and
less attractive ; the corolla is tubular and five-toothed ;

Fig. 123. Florets of Coltsfoot.— i, ligulate, female ray-floret;
2, tubular, male disk-floret ; Pa, pappus ; ov, ovary.

at the base, honey is secreted ; the ovule in the ovary
is abortive ; there are five stamens with joined anthers,
and the style has a pollen-brush, but not a functional
stigma. 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 pol-
lination are increased by the prolonged flowering-period.

The Dandelion. — Compare the flower-head of the Dande-
lion (Fig. 104) with those of the Daisy and Coltsfoot, and
notice that the hollow stalk is devoid of leaves.1 The

1 All parts of the plant contain a milky juice or latex, a fluid
which consists partly of waste substances, and to some extent of
nutritive materials. The latex is contained in irregular channels
known as laticiferous vessels.

BIOLOGY OF THE FLOWER

181

bracts of the involucre are in two whorls. The small outer
ones become recurved when the bud opens, and the inner,
larger ones stand erect and protect the florets. These
are all alike and ligulate, and, though small, are very con-
spicuous when massed together in the capitulum ; the
corollas are yellow, but the outer, more exposed ones are
often brown on the back. Cut the capitulum longitudi-
nally and note that the florets spring from the expanded,
flattened end of the inflorescence-
axis, the outer ones being the
oldest. Examine a floret (Fig. 124)
and note that the ovary is inferior,
and above it is a short neck on
which is the calyx, represented by
numerous hairs which form the
pappus. The corolla is irregular,
tubular below and strap-shaped
above, ending in five small teeth
representing the corolla-lobes. The
five stamens are fixed to the
corolla, the anthers are joined into
a tube round the style, and the
pollen is shed into the tube while
the style is yet short. Honey is
secreted by a ring at the base of
the corolla and rises high in the
tube, thus being accessible to many

kinds of insects. When the style elongates it is seen to have
two stigma-lobes and to be covered with hairs, which brush
the pollen out of the anther-cylinder. The stigmas curl
outwards, and their upper surfaces are covered with
papillae which receive pollen brought by insects from
another flower-head ; or self-pollination may occur by the
back-rolled stigmas coming into contact with pollen from
the same flower.

nc-

Fig. 124. Floret of
Dandelion. — a, united
anthers ; nc, neck ; ov,
ovary ; p, corolla ; Pa,
pappus ; st, stigma.

182

THE REPRODUCTIVE ORGANS

The Dandelion is visited by a great variety of insects
which are able to obtain both pollen and honey very readily.
Its flowering-period is a long one, but if the flowers are
out too early or too late for insect-visits self-pollination
is possible.

Flowers of the Potato and the Woody Nightshade or

Fig. 125. i, Woody Nightshade ; 2, vertical section
of flower ; 3, stamen ; p, pore.

Bittersweet agree with Composite flowers in one respect,
viz. the anthers are joined to form a tube (syngenesious).

The Woody Nightshade (Fig. 125) is frequent in hedge-
rows and is a lax climber. The flowers (Fig. 125, 2) are
small and in irregularly-branched inflorescences called
panicles. The calyx of each flower has five united sepals ;
the corolla has five purple, united petals, upon which are

BIOLOGY OF THE FLOWER

183

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 projects the two-
lobed stigma. When ripe the anthers dehisce by pores
at their free ends (Fig. 125, 3).
The pistil is superior, and
consists of two united carpels
placed obliquely in the flower
(Fig. 173) ; the ovary is two-
celled with many ovules on
axile placentas. The flower
secretes no honey, but is
visited by bees for pollen.

Irregular and specialized
flowers. — The Germander
Speedwell (Fig. 126) is pol-
linated mainly by drone-flies,
and shows several interesting
modifications. The flower (2
and 3) has four sepals, the
fifth posterior one being ab-
sent. The blue corolla has
four petals, but the large
posterior one really represents
two fused petals. All are
joined into a short tube.
There are only two stamens,
and these spread out hori-
zontally. The pistil consists
of two united carpels, and the
style projects over the anterior petal. A fleshy disk below
the ovary secretes honey, which is protected from rain by
hairs on the corolla.

As the fly alights, it first touches the stigma, then grasps
the two stamens, pulling them to the sides of its body,

Fig. 126. 1, Germander
Speedwell ; 2, flower showing
the position of the stamens and
style ; 3, flower in vertical
section ; a, stamens ; br, bracts ;
/, opposite decussate leaves :
r, raceme ; st, style.

184

THE REPRODUCTIVE ORGANS

Fig. 127. Flower of Violet. — i, solitary axillary inflorescence ;
2, a leaf ; 3, flower in vertical section ; 4, stamens and pistil ;
5, pistil removed ; 6, seed ; c, membraneous prolongation of
anther-connective; /, flap of stigma; n, nectary; s, spur; s.P,
stigmatic pit ; st, foliaceous stipules.

BIOLOGY OF THE FLOWER 185

which thus becomes dusted with pollen. On visiting
another flower the ripe stigma becomes dusted with pollen
from the body of the insect.

Violet and Pansy. Cleistogamous flowers. — The flowers
of the Violet and Pansy are curiously modified in all their
parts, and these should be carefully examined (Figs. 127
and 128). Note that the five free sepals are prolonged
downwards below their points of attachment. The corolla
consists of five free, dissimilar petals, the lower anterior one
being produced into a tubular spur. There are five stamens
attached by very short stalks and bearing orange-coloured
membraneous outgrowths at the ends
of the anthers (Fig. 127, 4 c). Notice
that the two stamens opposite the
spurred petal have each a long fleshy
nectary projecting into the spur (Fig.
127, 3 and 4). These secrete honey
which collects in the spur. The lines
on the petals point towards this re-
ceptacle, direct the insect to the honey,
and hence are called honey-guides. floral Diagram
The pistil is superior and consists of of Violet.

three united carpels. The style is bent
at the base and terminates in a rounded knob (Fig. 127, 5).
Look for the little pit on the lower surface of the stigma ;
on the edge of it is a little flap. The pollen is shed on to
the spurred petal, and an insect, visiting the flower to
obtain the honey, becomes dusted with pollen. On visiting
another flower it. brushes the flap, leaving pollen on it. and,
on quitting the flower, presses the flap into the stigmatic
pit, and so effects cross -pollination.

In the Sweet Violet the stigma is not globular.

Violas and Pansies both belong to the same genus Viola,
but if the flowers are compared, differences will be noted
in the arrangement of the petals. The lateral petals of

186 THE REPRODUCTIVE ORGANS

Violas are horizontal (Fig. 129, 1), while those of Pansies are
directed upwards (Fig. 129, 2). These differences may be
somewhat masked in cultivated forms with very large
petals. Irregular (zygomorphic) 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 typical 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 over-
shadowed 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 same

Fig. 129. plant. Similar closed flowers

1, Flower of Viola. a ttt

2, Flower of Pansy. occur ln the Wood Sorrel and

Henbit - Deadnettle (Lamium

amplcxicaide) . Such flowers are called cleistogamous (Gr.
kleistos — closed). Cold, absence of sunshine, and a poor
soil, favour their development.

Columbine, Monkshood, and Larkspur. — The Columbine
(Fig. 130) is a humble-bee flower. Its sepals are coloured ;
its five free petals are prolonged into large spurs whose
curved and fleshy ends secrete honey. The stamens are
indefinite, but the inner ones do not produce pollen. Such
barren stamens are called staminodes. In the centre are
the five carpels slightly joined at the base. The stigmas
ripen later than the stamens. The flower is pendulous, and
the bee, in order to obtain the honey, has to cling to the
base of the spur and also to the column of stamens and

BIOLOGY OF THE FLOWER

187

carpels. It thus becomes dusted with pollen, which it
carries to older flowers where the stigmas are ripe.

It requires an insect with a long proboscis to obtain the
honey from so long a tube. Often, however, the humble-

Fig. 130. 1, Vertical Section of Flower of Columbine; 2,
Vertical Section of Flower of Monkshood; 3, Side View of
Flower of Larkspur ; 4, front view of the flower; 5, flower in
vertical section; n, nectary; p, petals; s.P, honey-secreting spur
of 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. 130, 2) is another humble-bee

188 THE REPRODUCTIVE ORGANS

flower, and the plant grows wild only where humble-bees
are found. It has five blue sepals, the posterior one forming
a large hood which protects the anthers and nectaries.
The two posterior petals are modified to form long, clawed
nectaries or honey-leaves («) and the other petals are
usually absent. The stamens are indefinite and they ripen
before the stigmas (i. e. they are proterandrous) .

The Larkspur (Fig. 130, 3, 4, 5) has five sepals and two
spurred petals ; the posterior sepal is prolonged into a
membraneous spur which encloses the honey-secreting spurs
of the two posterior petals. The flower of the Columbine
is regular, while those of Monkshood and Larkspur are
irregular.

Sweet-Pea, Scarlet-Runner, and Gorse. — The Sweet-Pea
(Fig. 131) 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. 131, 2). The large posterior petal is the
standard (s), the two lateral ones are the alae or wings (a),
and the two anterior ones, which are slightly joined, form
together the carina or keel (k). Note carefully how these
are 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. 131, 3). When the stamens are united by their
filaments into two sets they are said to be diadelphous.
The filaments and style are bent upwards at the end of the
keel. Honey is secreted by the bases of the stamens, and
collects in and is protected by the stamen-trough (s.tr).

A clever insect like the bee is required to open the flower
and obtain the honey. It uses the wing-petals as an
alighting stage ; but these being articulated with the keel,
both are depressed by the weight of its body. When the

BIOLOGY OF THE FLOWER

s.hr. 3.

Fig. 131. 1, Sweet-Pea; 2, corolla; 3, flower with corolla
removed ; 4, fruits ; 5, seedling ; 6, 7, and 8, the first, second,
and third foliage-leaves ; a, alae ; c, calyx ; k, keel-petals ; I,
leaflet ; m, midrib ; p, petiole ; s, standard ; sg, stigma ; st,
stipule ; s.tr, stamen-trough ; t, leaflet-tendril.

igo THE REPRODUCTIVE ORGANS

bee pushes its proboscis into the tube, it obtains the honey
through 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 hairs at the end of the
style and dusts the under surface of the bee. When the bee
flies away, the keel springs back to its former place. If at
this time the stigma is ripe, it may be touched with pollen
as the keel returns to its place ; self-pollination would thus
occur. As the bee flies from flower to flower it may deposit
pollen on the stigma of another flower of the same species
and so effect cross-pollination.

The pistil (Fig. 131, 3) consists of one carpel (apocarpous),
and is covered with hairs. Look for the small ovules
within the ovary.

Other pea-like flowers should be compared with the
Sweet-Pea, and their characteristics 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 times. The Scarlet-
Runner, however, is peculiar in that the keel and style are
spirally coiled. The flower of the Garden Pea is regularly
self-pollinated. No European insect is strong enough to
open the flower and pollinate it. The White Clover pro-
duces 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 their former position
within the keel.

The Gorse (Fig. 132) differs in several respects from the
above. All the stamens are united to form a tube ; no
honey is secreted, and the flowers are visited by bees and
other 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 under side of its body is first

BIOLOGY OF THE FLOWER

191

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 their former position.
If the bee is dusted with pollen from another flower, cross-
pollination will occur ; if not, self-pollination may take
place as the insect leaves the flower. Imitate the action of
the bee by depressing the keel with a pencil and watch the

Fig. 132. Gorse. — I, leaf ; s, spine.

explosion. Such explosive flowers can profit only by one
visit.

Summary of the various grades of flower- structure. — Flowers
may be regarded from two points of view : — (1) the
Biological, which is concerned with the functions of the
flower and its relations to the outside world, especially wind
and insects. In the series of flowers which we have studied,
we find an increase in complexity of structure from simple
wind-pollinated flowers to more complex insect-pollinated
flowers, and in the latter, commencing with 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,

192 THE REPRODUCTIVE ORGANS

a union of sepals and petals, production of honey and scent,
and at the end of the series we arrive at special forms with
irregular flowers. These are so constructed as to exclude
the 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 simpler flowers are small, green, and incon-
spicuous, a stage higher the petals are larger and yellow or
white, while the tubular and more complex flowers are
often red, blue, or violet.

(2) The Morphological 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 Poplar and
Willow have no calyx or corolla. Their flowers are uni-
sexual 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 the
same tree, i. e. they are monoecious. The Anemone, Butter-
cup, Marsh Marigold, Columbine, Monkshood, and Larkspur
are hermaphrodite, and though differing much in form and
colour, all agree in possessing a free calyx and corolla,
numerous hypogynous stamens, and a superior apocarpous
pistil. 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 six 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 irregular corolla,
one petal being spurred. The pistil consists of three united
carpels and a one-celled ovary.

Important differences from the above are met with in

BIOLOGY OF THE FLOWER 193

the Strawberry and the Rose. While the sepals and petals
are free and the stamens indefinite, as in the Buttercup,
these parts are developed on the edge of the hollow recep-
tacle ; they are therefore around, and not below, the ovary
— thus being perigynous. The carpels are numerous and
apocarpous.

The irregular flowers of the Sweet-Pea and Gorse also
have perigynous stamens, but only one (apocarpous) carpel.

The Chervil flower is also irregular, but the sepals, petals,
and stamens are developed on the top of the ovary
(epigynous), the inferior ovary being syncarpous.

In all these cases the petals are free (polypetalous).

In the remaining examples the chief difference we noticed
was that the petals were united to form a tube (gamo-
petalous).

In the Heath, the corolla is bell-shaped ; the anthers
possess small appendages or horns, and the pollen escapes
through pores. The ovary is superior. In the Primrose
the five petals are joined, forming a long, narrow tube to
which are attached five stamens. The superior ovary has
only one chamber with free-central placentation. The
corolla of the Speedwell is also gamopetalous, and on it
there are two stamens ; the ovary is superior and two-
celled. In the Daisy and Dandelion, the flowers, though
small, are massed together into a head, or capitulum. The
petals are joined, and the five stamens on them have their
anthers united round the style. The ovary is superior, and
when mature has only one chamber containing a single
ovule.

It is upon such characters in the structure and arrange-
ment of the parts of the flower that the classification of
plants depends ; and it is by comparison of these characters
on the lines indicated that we gain an insight into plant
relationships. All the plants we have just considered agree
in a few broad characters. The vascular bundles of the

1296 V

i94 THE REPRODUCTIVE ORGANS

stem are arranged in a ring ; the leaves are net-veined ;
and the parts of the flower are usually disposed in fours or
fives. Further, the seeds have two cotyledons, and they
therefore all belong to the same great class of flowering
plants called Dicotyledons.

We now proceed to a few examples belonging to the
other great class, the Monocotyledons.

CHAPTER XIV

BIOLOGY OF THE FLOWER (Continued)

Monocotyledons

Hypogynous flowers, with 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 Bluebell
arise on the upper part of a long leafless axis or scape
(Fig. 133, 1). Each flower (Fig. 133, 2) is attached by
a stalk or pedicel, at the base of which are two long, narrow,
coloured bracts which cover the young flowers when in
bud (br). An inflorescence of this kind with stalked
flowers, of which the oldest is at the bottom and the others
are in succession younger as we near the top, is called a
raceme.

The parts of the flowers are arranged very regularly in
threes (trimerous). On the outside are three sepals, then
three petals, and the six are slightly joined together at
the base. Here the sepals and petals are all similar and
coloured, and the name perianth may be used to indicate
the two whorls when they are not differentiated into calyx
and corolla. There are six stamens, three outer and three
inner, fixed below the pistil, which is in the centre and

BIOLOGY OF THE FLOWER

195

consists of three united carpels. The ovary is superior and
divided into three chambers, and above it 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)

Fig. 133. Wild Hyacinth.
— 1, racemose inflorescence ;
2, vertical section of flower ;
br, bract ; ov, ovary ; Pe,
pedicel ; s, scape.

Fig. 134. Vertical Section of
Daffodil Flower. — co, corona ;
ov, ovary ; sp, spathe.

dehisce inwards (introrse dehiscence), then turn horizontally
and 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 if cross-pollination does not occur,
self-pollination is certain, as the three stigma-lobes when
ripe come into contact with the anthers.

Epigynous trimerous flowers.- — The Daffodil has three

N 2

ig6 THE REPRODUCTIVE ORGANS

outer and three inner perianth-leaves united into a tube,
an outgrowth from which forms a large bell-shaped corona
(Fig. 134, 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 gradations
may be found from this up to the large corona of the
Daffodil. The six 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 three carpels and the
ovarj' is three-celled, with axile placentation. The bract
of the Daffodil is in the form of a dry membraneous sheath
or 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 slender 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 young
corm forming as a branch upon the old one (Fig. 135).

Remove the foliage-leaves and note their mode of attach-
ment (see p. 133 and Fig. 84). The flower is surrounded by a
thin, colourless sheath (Fig. 135, sh), and is supported on an
under-ground cylindrical stalk — the scape (sc). The perianth-
leaves 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),

BIOLOGY OF THE FLOWER

197

and are ripe before the stigmas. Look for the ovary (ov)
and note its position in relation to the ground-level (g).
A section across it shows it to be three-celled and to con-
tain many ovules on axile placentas. The ovary is inferior
and lies one to two inches below the surface of the soil.

sc.

Fig. 135. Vertical Section,
Corm and Flower of Crocus. —
a, anther; c.i, old corm; c.2,
young corm ; g, ground-level ;
ov, ovary; p, perianth-tube ; sc,
scape; sh, sheath; st, stigma;
sy, style.

Fig. 136. 1, Inflo-
rescence of Iris. 2,
flower with outer peri-
anth-leaves removed ; a,
anther ; ov, ovary ; sp,
spathe ; st, stigma ; sy,
petaloid style.

Arising from the top of the ovary, and nearly filling the
perianth-tube, is a very long style which divides at its free
end into three large, frilled stigmas (st). The ovary secretes
honey which rises high in the tube and so comes within reach
of the long-tongued bees, but only insects with very long

ig8 THE REPRODUCTIVE ORGANS

tongues (such as the hawk-moths) are able to extract the
whole of it. Insects visiting the flower for honey will at
first become dusted with pollen, which may be transferred
to 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 Iris (Fig. 136) has three large outer
and three small inner perianth-leaves, 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 petaloid lobes,
against which lie the stamens. On the under side of these
lobes and near the tip is a little flap covering the stigmatic
surface. As in the Daffodil, the flowers are enclosed in
a large spathe. The petaloid style arms (sy) of the Iris are
often applied to the perianth-leaves in such a way as to form
a split tube, at the base of which are honey-glands. The
difference in size of the perianth-leaves, together with the
large petaloid styles, gives to the Iris a striking, and at first
rather puzzling, appearance.

The Orchid flower. — Still more puzzling is the flower of the
Purple Orchis (Fig. 137). Each flower arises in the axil
of a bract and appears to be stalked, but the stalk consists
of the inferior ovary and is twisted (2, ov). Hence the flowers
are sessile 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. 137, /), 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-

BIOLOGY OF THE FLOWER

199

pressed. Two of them, however, are represented by small,
barren stumps, called staminodes [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
side of it is a stigmatic surface.

Imitate the action of a bee by inserting the point of
a pencil into the throat of the flower, and in doing so press
it against the rostellum. Now remove it, and if the stamen

Fig. 137. Purple Orchis. — 1, front view of flower; 2, side
view of flower ; 3, pollinium ; 4, anther- and stigma- lobes ; 5,
pollinium removed from a flower and bending horizontally ; a,
anther ; I, labellum ; ov, ovary ; p, pollinia ; r, rostellum ;
s, stigma ; sp, spur ; st, staminodes.

is ripe, notice that two stalked, club-shaped masses of pollen
adhere to the pencil (Fig. 137, 5). These are called pol-
linia (p), and are the masses of pollen from the anther-
lobes. Watch them for a moment and note that they bend
into a horizontal position, turn outwards a little, and are
therefore suitably placed for coming into contact with the
stigmatic surfaces when again inserted into a flower. Try
to brush the pollinia off the pencil and you will find that
the secretion glues them so firmly to the pencil that some
force is required to remove them.

200 THE REPRODUCTIVE ORGANS

The Orchid illustrates great modification in a mono-
cotyledonous flower. The perianth is irregular (zygomor-
phic) ; the posterior petal of the inner whorl projects as
a lip or labellum, and serves as an alighting 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) — on which
are 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 fruit contains a large number of
minute seeds.

Reference to the floral diagram (Fig. 179) will help to make
the various relationships clear. Six stamens, in two whorls of
three each, ought to be present, but of the outer whorl only
the anterior one is present, and it is over the rostellum.
The other two are suppressed, and their position is
represented in the diagram by a cross x . Of the inner
whorl, the posterior stamen is suppressed, and the two
lateral ones are reduced to short, barren stumps called
staminodes. The anterior stigma is transformed into
the rostellum ; the two lateral ones are functional and lie
below the stamen, one on either side of it. As the flower
develops, the stalk-like inferior ovary twists through 1800,
and carries all the parts of the flower round, so that the
posterior lip comes to be anterior in the open flower. The
diagram (Fig. 179) represents the parts before twisting
occurs.

Flowers of Grasses. — The flowers of Grasses are small,
and the parts can be made out only by careful observation.
The inflorescence is usually either a compound spike or
a panicle ; and what appears to be a single flower is a group
of sessile flowers, or spikelets (Fig. 138, 1). A dissected

BIOLOGY OF THE FLOWER

201

spikelet of Wheat is shown in Fig. 138, 3, and the arrangement
of the parts on the axis is shown in the diagram Fig. 138, 2.
At the base of it is a scale (g), the outer glume ; imme-

Fig. 138. Flowers of Grasses. — 1, spikelet of Meadow Poa
2, diagram of Grass spikelet ; 3, parts of a Wheat spikelet dissected
4, parts of flower of Vernal-grass dissected ; 5, floral diagram
a, anther ; g, glume ; /, lodicule ; ov, ovary ; p, pale ; st, stigma.

diately above it is another scale, the inner glume ; and
higher still is a smaller and thinner scale, the outer pale,
in the axil of which a flowering branch arises. Low on the

202 THE REPRODUCTIVE ORGANS

flower-stalk is a fourth scale, the inner pale ; then follow
two minute scales called lodicules (/), immediately above
which 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 it are two large, feathery
stigmas. There is no perianth unless the two lodicules
may 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. 138, 4), in which flower there are no lodi-
cules and only two stamens. In most cases the stamens
ripen and shed their 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 stigmas,
are excellent devices for wind-pollination ; while the fact
that the anthers and stigmas of the same flower are not
ripe at the same time secures cross-fertilization.

To summarize : The flowers of Monocotyledons show
a series of modifications, from simple types pollinated by
the wind to complex forms adapted to the habits of special
insects. The Grasses, like the Willows, have no perianth,
and the essential organs are enclosed by bracts called
glumes and pales. The three stamens with their slender
filaments and large versatile anthers, and the branched
stigmas, 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 each ;
the perianth is petaloid ; the syncarpous ovary is superior,
three-celled, and contains many ovules. The Daffodil
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

BIOLOGY OF THE FLOWER 203

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 greatest
specialization occurs in the Orchids, which have irregular
flowers, long honey-secreting spurs, stamens reduced to one,
rarely two, and united to the style (gynandrous). They
are usually incapable of self-pollination. The capsules
produce an immense number of minute seeds.

CHAPTER XV

POLLINATION, FERTILIZATION, AND THE
ORIGIN OF SEEDS

From our study of flowers we learn that all the parts
of which they are composed serve directly or indirectly to
secure the production of seeds. The modifications are very
numerous, but in most cases they are definitely related
to pollination, which precedes fertilization. Except in rare
cases, ovules must 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 means by which this is secured may be sum-
marized as follows :

1. Self-pollination, where the pollen falls on to the stigma
of the same flower. This occurs in flowers which never
open, like some of the Violets and Wood Sorrel, also in
certain species of Deadnettle and Vetch. These are known
as cleistogamic flowers (see p. 186). Self-pollination is
very common in flowers where the pollen and stigma are
ripe at the same time, e. g. in the Buttercup, Dwarf Mallow,

204 THE REPRODUCTIVE ORGANS

Scarlet Pimpernel, Stock, and Crocus. It is an effective
means of securing a crop of seeds if cross-pollination fails.

2. Cross-pollination, 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 resulting from such a cross are
often more numerous and produce better and healthier
plants than when self-pollination occurs.

The more important means of securing cross-pollination
are :

i. Stamens and pistil occurring in different flowers (dicli-
nous : Gr. di = double, Mine = a bed).

(a) Staminate and pistillate flowers on the same plant
(monoecious), e. g. Pine, Hazel, Oak, and Birch.

(b) Staminate and pistillate flowers on separate plants
(dioecious), e. g. Willow, Poplar, Red Campion, Dog's
Mercury, Crowberry.

2. Stamens and pistil occurring in the same flower
(hermaphrodite), but are not ripe at the same time (dicho-
gamous : Gr. dicha = in two parts), though the male and
female stages usually overlap, at which time self-pollination
may occur.

(a) Stamens ripen and shed their pollen before the pistil
is ripe (proterandrous), e. g. Daisy, Dandelion, and other
Compositae ; Mallow, Wood Sorrel, Meadow Crane's-bill,
Chervil and other umbelliferous flowers.

(b) Pistils ripen before the stamens (proterogynous),
e. g. Field Wood-rush and Plantains.

3. Anthers and stigmas are so situated that the pollen
does not fall on to the stigma, e. g. Pansy, Buttercup (see
pp. 167-8).

4. Different forms of flowers occur in the same species
(heteromorphic, Gr. hetero = different).

(a) Long- and short-styled forms (dimorphic), e. g.

POLLINATION 205

Primrose, Cowslip (see p. 176), and some species of Sorrel
(Oxalis) .

(b) Long, intermediate, and short-styled forms (tri-
morphic),e. g. Purple Loosestrife (Lythrum Salicaria) , and
some species of Sorrel {Oxalis).

As the pollen-grains are unable by their own efforts to
reach the stigmas, they must be carried by external agents,
the chief of which are the wind and animals. Flowers
differ in several important respects, according to the agent
employed in the transference of pollen.

1. Flowers pollinated by the Wind (anemophilous :
Gr. anemos = wind, philos = loving) have usually the
following characteristics :

The flowers are small, not showy, unscented, and without
honey ; the anthers are large and on long slender filaments ;
and sometimes, as in catkins, the whole inflorescence is
easily shaken by the wind. The pollen is abundant, dry,
and powdery. The stigmas are large and feathery, and
expose a large surface to catch the pollen ; but much of the
pollen never reaches the stigmas and is wasted. Many of
our forest trees are wind-pollinated, e. g. Pine, Larch,
Poplar, Hazel, Oak, Birch, Beech; also the Grasses and
Sedges, Docks, Plantains, Stinging Nettle, and Crowberry.

2. Flowers pollinated by Animals (zoophilous : Gr. zdon
= an animal) are the more familiar and attractive species.
The most important pollinators are Insects, and the
flowers so pollinated are said to be entomophilous (Gr.
entomon = insect) . Flowers possess several features which
render them attractive to insects. They are usually
brightly coloured, often scented, and have nectaries. The
pollen is sticky, readily adheres to the bodies of insects,
and is often collected by thern as food. The stigmas are
small and frequently placed in a position favouring pollina-
tion by the insect visitor. Small animals like snails may
bring about pollination when crawling over certain flowers,

206 THE REPRODUCTIVE ORGANS

and some, often scarlet exotic flowers, are pollinated by
humming-birds.

Positions 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 stamens
in the Wallflower and Stock ;

(b) On the sepals of the Mallow and Coronilla ;

(d) On the stamens of the Violet and Pansy, the spur
acting as a honey-receptacle ;

(e) On the carpels of the Marsh Marigold and Bluebell.

Nectaries sometimes occur on leaves (extra-floral nec-
taries) (Fig. 219, p. 340). These attract numerous ants,
which in turn keep off the caterpillars that would eat the
leaves.

Fertilization and the Origin of Seeds

Structure of the pistil. — The pistil is the inner essential
organ of the flower. In a typical and simple case like that
of the Pea it may be regarded as an up-rolled leaf (Fig. 139),
bearing on its margins small rounded bodies called ovules (0).
If we suppose the turned-in edges to meet and fuse, so
enclosing the ovules in a box, we can form some idea of its
structure. The ovule-bearing portion is called the ovary (ov) ,
and that part of the edge from which the ovules spring is
called the placenta (pi). Its tip is prolonged and known
as the style, and at the end of it 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 Stock the pistil is composed of two united carpels ;
in the Clematis, Buttercup, Marsh Marigold, and Rose, it

FERTILIZATION AND THE ORIGIN OF SEEDS 207

consists of many free carpels. When the pistil consists
of one or more free carpels it is said to be apocarpous ;
and when of two or more carpels united together, it is syn-
carpous. If it arises above the other parts (calyx, corolla,
and stamens) it is superior, and if below, it is inferior.

Sometimes botanists use the word ' pistil ' in a different
sense. When the carpels are free each consists typically
of an ovary, style, and stigma. Then
the flower is said to have many
pistils, e. g. the Buttercup ; but
when the carpels are joined, as in
the Stock and Tulip, the flower is
said to have only one pistil. The
name gynoecium is given to the
central part of the flower, whether
consisting of one carpel or many,
free or joined.

The ovule and the embryo-sac. —
When the ovule first appears on
the placenta it consists of a small
outgrowth of tissue, the nucellus
(Fig. 140, n) . Around the base of this,
two coats grow upwards and cover
the nucellus, with the exception of
a minute pore, which remains at the
end and forms the micropyle. Within
the nucellus a large cell arises, called
the embryo-sac (em), within which

several cells are formed, one of these, near the micropyle,
being called the egg-cell.

Fig. 140, 1-3, illustrates these points. In these the ovule
is 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 is brought
down to the base of the ovule stalk or funicle. Such an

Fig. 139. Diagram
of opened Pistil. — f,
funicle ; o, ovule ; ov ,
ovary ; PI, placenta ;
Po, pollen -grains ; P.t,
pollen-tube ; s, stigma ;
sy, style.

208

THE REPRODUCTIVE ORGANS

inverted ovule is said to be anatropous (Fig. 141, 2) (Gr.
ana, denoting inversion, trepo = I turn). A straight one
is orthotropous (1) (Gr. orthos = straight) ; when curved
it is campylotropous (3) (Gr. kampylos = curved) ; and
when at right angles to the funicle, amphitropous (4)
(Gr. amphi = on both sides).

Fig. 140. Development of an Ovule. — em, embryo-sac ;
n, nucellus ; p, outer integument ; s, inner integument.

Fig. 141. Forms of Ovules. — 1, orthotropous ; 2, anatropous ;
3, campylotropous ; 4, amphitropous ; em, embryo-sac ; /, funicle ;
n, nucellus ; p, outer coat or primine ; s, inner coat or secundine.

When the ovule has developed thus far it 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, and fertilization. — By means
of a simple experiment a good idea may be obtained of
what occurs. Place a drop of 10 per cent, solution of cane
sugar on a glass slip and put into the solution a few pollen-
grains of the Sweet-Pea. If examined after an hour or two,
short, delicate tubes called pollen-tubes will be seen emerg-

FERTILIZATION AND THE ORIGIN OF SEEDS 209

ing from the grains, and into these the contents pass as
a living stream (Fig. 142).

When pollen-grains are placed on the stigma of a pistil,
growth of this kind occurs. The pollen-tubes grow down-
wards through the style, enter the cavity of the ovary, and
reach the micropyle of the ovule. Into this the tube passes,
and the essential part of its contents enters the embryo-
sac and there accomplishes the process of fertilization by
fusing with the nucleus of the egg-cell. It is not until such
fertilization has taken place that the ovule develops into
a seed ; for if the stamens are removed from a flower before

Fig. 142. Germinating Pollen-Grains. — n, nucleus ;
p, protoplasm ; P.g, pollen-grain ; P.t, pollen-tube.

the anthers are ripe and the flower is covered so that no
insect can carry pollen to it, the pistil is unable to set ripe
seed, although it may enlarge considerably and in some
cases become fleshy.

Changes produced by fertilization. — After the egg-cell is
fertilized, the rest of the embryo-sac becomes filled with
tissue called endosperm. In the Pea and the Bean the
fertilized egg-cell grows at the expense of the endosperm,
develops into an embryo, and at the same time the nucellus
is absorbed. Thus, when the seed is ripe it contains no
endosperm.

1290

210 THE REPRODUCTIVE ORGANS

The differences between ovule and seed are important
and may be stated as follows :

Ovule. Seed.

Before fertilization. After fertilization.

2 ovule coats 2 ovule-coats Seed-coat

Nucellus Nucellus [Nucellus and

Embryo-sac Embryo-sac endosperm used

Endosperm up as food for]

Egg-cell Young embryo 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 this
occur in Wheat, Maize, Common Ash, and Castor Oil. Occa-
sionally some of the nucellus persists, when it is called
perisperm.

Thus food-reserve may be stored in various regions in
a seed : in the cotyledons of the embryo (Bean), in the
endosperm of the embryo-sac (Wheat, Ash), and in the
perisperm or persistent nucellus (Water-lity, Pepper).

The ovule is not the only part affected by fertilization ;
many surrounding parts are affected also :

In the Pea, the carpel grows enormously and forms the
pod. In the Stock, the two carpels elongate greatly. In
the Strawberry, Rose, Apple, and Pear, the receptacle
becomes not only very large but fleshy. In the Winter
Cherry (Phy sails), the calyx becomes much inflated and
brightly coloured. In the Fig, Mulberry, and Pine-apple,
the whole inflorescence or parts of it become fleshy, fuse
together, and form a very complex aggregate fruit.

The changes that take place as a result of fertilization
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 starting-
point in the life-history of a new plant. The growth-
stimulus produces the changes we have outlined both

FERTILIZATION AND THE ORIGIN OF SEEDS 211

within the ovule and in adjacent 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 as
a result of fertilization. In the Pea and Bean, this con-
sists 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, sometimes
united as in the Violet and Crocus.

In common edible fruits the fleshy part which is eaten,
often consists of structures other than the pistil. These
are known as false fruits, while those formed from the
pistil only are known as true fruits.

In all cases the object of their formation is the produc-
tion of seeds, containing a young plantlet capable of growing
into a new plant. In some fruits the fruit-coat or pericarp
is dry and does not split until the seed within germinates ;
in others, the fruit-coat splits and the seeds are scattered.
Others, again, have a succulent or fleshy fruit-coat, and
most of our edible fruits belong to this class. A few speci-
mens of each kind should be obtained and carefully studied.

Dry indehiscent fruits. — -The Hazel-nut (Fig. 187, 8)
is enclosed in a cup consisting of large, leafy bracts.
Break open the hard, dry shell and note the single seed
within (sometimes two may be found). Look for the

0 2

212

THE REPRODUCTIVE ORGANS

seed-stalk and notice how it is attached. The seed-coat is
thin 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 (Fig. 143). Here the
bracts are numerous, small, and form a compact cup. The
smooth fruit-coat encloses one seed, the embryo has two
large fleshy cotyledons. Such hard, dry, one-seeded fruits

cu.

Fig. 143. Fruit of Oak. — i, Acorn with cupule ; 2, vertical
section of same ; c, cotyledon ; cu, cupule ; /, remains of flower ;
p, plumule ; Pe, pericarp ; r, radicle ; t, testa.

are called nuts. The Sweet Chestnut and the Beech are
other examples.

The fruit of the Buttercup (Fig. 144) consists of many
small, 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. 145) is very similar, but the
receptacle is slightly hollowed, and from its centre grows
a large, fleshy structure, in which the achenes are embedded.

The Rose-hip (Fig. 146) differs from the above in that the

STRUCTURE OF FRUITS

213

Fig. 144. Fruit of Butter-
cup.— 1, aeterio of achenes ; 2,
section of an achene ; e, endo-
sperm ; em, embryo ; Pe, peri-
carp ; st, stigma ; t, testa.

Fig. 145. Vertical Sec-
tion of a Strawberry. —
a, remains of stamens on
edge of receptacle ; ac,
achenes ; /, fleshy outgrowth
of receptacle ; r, receptacle.

Fig. 146. Vertical Section
of Hip of Rose. — a, remains of
stamens on edge of receptacle
cup ; ac, achenes ; c, calyx ; r,
hollow receptacle ; st, stigmas.

Fig. 147.

Fruit of Dandelion.

ov, ovary.

214

THE REPRODUCTIVE ORGANS

receptacle is hollowed and bears the achenes on the inner
surface of the cup. Both in this and in the Strawberry
the fleshy part is the receptacle, and these fruits are there-
fore succulent fruits containing many dry indehiscent
nutlets.

Fruits like those of the Dandelion (Fig. 147), Coltsfoot,
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. 148. 1, 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 closely
adhere.

The Sycamore key (Fig. 202, 5) consists of two or more
carpels, which, when ripe, separate into part-fruits (meri-
carps) but do not scatter the seeds. Each part contains
one seed, and is provided with a wing. Cut open a fruit ;
observe the thick fruit-coat lined with a felt of hairs and the
seed within covered by a thin brown testa. Remove this
and examine the embryo carefully ; see how the cotyledons
are rolled up. Make a paper model to show clearly how
they are folded and rolled (Fig. 202, 6). Such winged fruits

STRUCTURE OF FRUITS

215

are called samaras. Other examples are the Maple, Ash,
Elm, and Birch.

Another common type which splits into two half-fruits
is found in the Hogweed, Chervil, and other umbelliferous
plants. A ripe fruit of the Hogweed (Fig. 148) is easy to
dissect. It consists of two flattened carpels, which readily
separate into two half-fruits (mericarps), and remaining
attached by a slender stalk, the carpophore (c), each

Fig. 150. 1, Siliqua of Shep-
herd's Purse ; 2, siliqua de-
hiscing; r, replum with seeds
attached.

Fig. 149.
Follicles of Columbine.

mericarp containing one seed. Such fruits are called
cremocarps. Caraway ' seeds ' are half-fruits of this kind.

Dry dehiscent fruits. — In all the above, when the fruit 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 allows the seeds to escape. These, not having
the protection of the fruit-coat, are usually surrounded by
a thick testa. They include many common fruits, and
several should be examined, and the different modes of
splitting (or dehiscence) compared.

The Columbine (Fig. 149), Monkshood, and Marsh

2l6

THE REPRODUCTIVE ORGANS

Mangold have a pistil of several free carpels. Each is
pod-like and contains many seeds ; but, unlike a pod,
splits along the inner seam only. These fruits are called
follicles. The legume or pod of the Pea and the Bean
consists of one carpel and splits along both seams, the two
valves often being twisted into a close spiral (Fig. 162, 1).
The Shepherd's Purse (Fig. 150) and Honesty are simi-
lar to the Stock, but shorter, and their pods are known as

Fig. 151. 1, Open Capsule of Violet; 2, Capslle of Poppy
dehiscing by pores ; 3, same in section ; 4, capsule of pim-
PERNEL dehiscing transversely ; p, pore ; 5, edges of carpels
which project into the ovary but do not meet in the centre.

siliquas. Compare these and note how very different forms
of fruit may arise from one type of structure.

A common type of dry splitting fruit which is more or
less globular 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. 159, 2).
In the Violet (Fig. 151, 1) it opens by three valves. Other
capsules dehisce by pores, as in the Poppy (Fig. 151, 2 and 3),
where the pores are around the margin ; and in the Snap-
dragon the capsule is oblique and has three pores (Fig. 159, 3).
In some Campanulas the pores are at the base (Fig. 159, 5) ;
while in the globular fruits of the Pimpernel (Fig. 151, 4),

STRUCTURE OF FRUITS

217

Henbane, and Plantain, the capsules split transversely and
the upper part comes away as a lid.

Succulent fruits. — We have seen (p. 215) that the pericarp
of many dry fruits splits when ripe, and the seeds, sur-
rounded by a thick testa, are dispersed. On the other hand,
the more familiar edible fruits have a succulent or juicy coat
which does not split when ripe ; that is, they are indehiscent.
Examine the fruit of a Cherry (Fig. 152) and note the thin

Fig. 152. Vertical Section
of Drupe of Cherry. — c, coty-
ledon ; e, epicarp ; en, endo-
carp ; m, mesocarp ; pi, plum-
ule ; r, radicle ; t, testa.

Fig. 153. Aeterio of
Drupels of Blackberry.
— a, remains of stamens ;
r, receptacle ; st, stigmas.

outer coat or epicarp, the fleshy middle coat or mesocarp,
and the hard inner coat, the stone or endocarp, enclosing
one seed.

The Plum and the Damson are fruits similar to the
Cherry, all three arising from a superior apocarpous pistil.
The name drupe (Gr. druppa = over-ripe olive) is given to
fruits of this kind.

Compare the above with the fruits of the Blackberry
(tig- I53) and Raspberry. Each of these consists of many
small drupes or drupels, borne on an upgrowth from the
centre of the receptacle.

2l8

THE REPRODUCTIVE ORGANS

The Gooseberry (Fig. 154), Grape, Currant, and Tomato
are syncarpous fruits, in which the endocarp is succulent as
well as the mesocarp, and they have one cavity (loculus)
which contains several seeds. Such fruits are known as
berries. The name berry is also given to many common

Fig. 154. Fruit of Goose-
berry.— 1, berry in vertical
section ; 2, in transverse sec-
tion ; c, remains of flower ; e,
epicarp ; m, mesocarp ; s, seeds FlG IS5_ pQME QF AppLE

embedded in succulent endo- _x> transverse section> show.

carP- ing the five carpels ; 2, ver-

tical section ; c, remains of
flower ; e, epicarp ; en, endo-
carp or core; m, mesocarp;
s, seed.

fruits like 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 like the Currant
and Gooseberry the fruit is inferior, the calyx being on the
top of the fruit ; while the Tomato, Grape, Orange, and

STRUCTURE OF FRUITS 219

Lemon are superior. The Pomegranate is peculiar in that
the edible 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 fruits in which the
receptacle takes part in their formation ; and they are
sometimes called false fruits or pseudocarps. In the
Apple (Fig. 155) the core is formed from the pistil, and the
pips are the seeds, while the fleshy part is formed from the
receptacle. Such a fruit is called a pome.

The Fig is a compound fruit consisting of a hollow inflo-
rescence, within which are numerous small drupes. The
Pine-apple is also a fleshy inflorescence, the axis of which is
continued 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 differing
widely from it in origin.

The modifications found in fruits have, in most cases,
an obvious connexion with the dispersal of seeds, the
various devices for which we will next consider.

CHAPTER XVII

DISPERSAL OF FRUITS AND SEEDS

Prior to August 1883, 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 vegetation.
This provided a rare opportunity of studying the ways

220 THE REPRODUCTIVE ORGANS

in which a barren island (about twenty-five miles from
the nearest mainland) acquired a new flora and fauna.

Colonization of a barren island. — It was found that the
first colonists were microscopic Blue-green Algae, Bacteria
and Diatoms, which formed slimy patches on the pumice
and ash, and provided a suitable medium in which, later,
the spores of Ferns and Mosses germinated. All these
bodies are so very minute that they float as dust in the
air, and are thus capable of being carried long distances
by the wind. In this way spores of these plants were
carried from the adjacent islands, and formed the first
elements of the flora. Then followed flowering plants
having light wind-borne fruits, 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 v/eeds that followed in
his 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 seeds
of 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 object to be attained is that seeds should be carried
far enough away from the parent plant to prevent over-
crowding, and to ensure that they are on suitable ground
unoccupied 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

DISPERSAL OF FRUITS AND SEEDS

221

device which increases the surface without greatly in-
creasing the weight of the seed, e. g. :

(i) Minute spores x of Fungi, Mosses, and Ferns, and also
microscopic plants. The frequent occurrence of moulds on
organic substances is due mainly to the ease with which
their abundant spores are carried in the air.

(2) Minute seeds, as of Orchids, which are rendered
lighter still in proportion to bulk by a light, loose, outer

8 «r 9

Fig. 156. Fruits and Seeds dispersed by the Wind. — 1, seed
of Orchid, much magnified ; 2, seed of Willow ; 3, seed of Pine ;
4, achene of Clematis ; 5 a, fruit of female flower of Coltsfoot ;
5 b, barren fruit of male flower of Coltsfoot ; 6, mericarp of Hog-
weed ; 7, samara of Elm ; 8, fruit of Hornbeam ; 9, rolled pod of
Medicago.

coat (Fig. 156, 1). Heaths also have extremely small
wind-dispersed seeds.

(3) Seed-Parachutes. Small seeds, even though larger
than those mentioned above, may bear tufts of hairs
serving as a parachute, e. g. Willows (Figs. 156, 2 and 157),
Poplars, Willow Herbs (Epilobium) (Fig. 158, 2), and Cotton
(the cotton fibres of commerce being highly developed
seed-hairs).

(4) Fruit-Parachutes. The small fruits of many Com-
positae and other plants have a pappose calyx, e. g.

1 Spores are minute reproductive cells capable of growing into
new plants. Fungi, Mosses, and Ferns never produce true seeds.

222 THE REPRODUCTIVE ORGANS

Groundsel, Dandelion (Fig. 147), Coltsfoot (Fig. 156, 5),
Thistles, Valerian, Bulrush ; and the perianth of the
Cotton-grasses (Eriophorum) (Fig. 158, 1) is transformed
into a tuft of long hairs. The Clematis (Fig. 156, 4)
and Mountain Avens have a long, persistent, feathery
style. The awn of the Feather-grass is twisted, and ends
in a beautiful plume a foot in length. Some Anemones
have hairy fruit-coats.

(5) Winged Seeds occur in the Pine (Fig. 156, 3), Larch,
and cultivated climbers like Eccremocarpus and Bignonia.

(6) The Flattened Fruits of the Hogweed (Fig. 156, 6)
split into two thin half-fruits and are readily detached from
their slender threads during high winds.

(7) Many fruits have a Winged fruit-coat, and the fruit
is often flattened, e.g. Birch, Elm (Fig. 156, 7), Common
Ash (Fig. 9, 1), Sycamore (Fig. 202, 5), and Maple. The
wings of the Hornbeam (Fig. 156, 8) are formed from
bracts. Most of these, however, are too heavy to be carried
far, except during high gales.

(8) Globular Fruits and Plants may be rolled to a slight
extent by the winds, as is the case with the fruits of
Medicago (Fig. 156, 9) and the whole plants of certain
species of Selaginella.

(9) Censer Mechanisms. The capsules and follicles of
many plants (Fig. 159, 1 to 5) are borne on erect stalks,
and the seeds can only escape from the cup-like fruit-case
when 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 heap
to the ground. We have already noticed the more im-
portant ways in which capsules open to allow the seeds
to escape. Those widely open above are liable to damage
by rain, but often the capsule is surrounded by teeth
which bend over and close the capsule in wet weather,
opening again when the air is drier (Fig. 159, 2). The fruit

Fig. 157. Willows in Fruit; Alders in the Background.

Fig. 158. 1, Fruits of Cotton Grass ; 2, Pappose Seeds
of Willow Herb.

DISPERSAL OF FRUITS AND SEEDS 223

of the Poppy (Fig. 159, 4) is permanently covered, the small
seeds escaping through pores just below the lid. In Cam-
panulas with pendulous capsules the pores are at the base
of the capsule (Fig. 159, 5). In either case a strong wind
or jerk is necessary to shake out the seeds.

B. Dispersal by water. — The dry fruits and seeds of
plants growing along the sides of rivers and lakes may be
blown into the water and float a short distance before
sinking, or washed ashore farther down stream, where
they may germinate ; generally, however, they sink
rapidly. If carried seaward, most of them soon lose their
power of germination after entering salt water. Trunks

Fig. 159. Censer Fruits. — 1, follicles of Marsh Marigold ;
2, capsule of Red Campion ; 3, capsule of Snapdragon dehiscing
by pores ; 4, capsule of Poppy ; 5, capsule of Campanula.

and branches of trees carried down stream often bear
seeds and fruits embedded in the mud adhering to them,
over long distances. Fragments of plants, especially of
water-plants capable of rooting, are often carried consider-
able distances, and provide an effective means of dispersal.
The Canadian Water-weed (Elodea), so common in our
ponds and canals, has spread extensively in Europe by
this means.

The seeds of the White Water-Lily are surrounded by
a spongy aril, and between it and the seed-coat is air, which
enables the seeds to float until the air escapes, when they
sink to the bottom. In the Frog-bit and some Pond-weeds,
buds are formed in the autumn which become detached

224 THE REPRODUCTIVE ORGANS

and sink to the bottom ; the rest of the plant may die
down, the species being renewed the next season by the
buds which then renew their growth. Such buds enable
the plants to tide over the winter, and are called winter-
buds.

C. Dispersal by animals. — (i) Fungi growing in a pasture
commonly occur on the dung of browsing animals ; some
of the spores may have been carried thither by the wind,
but a common occurrence is that spores adhering to the
leaves of plants are eaten by animals and pass uninjured
through their food-canal. On the way they are partly
digested and this prepares them for germination. Some
fungus spores germinate with difficulty until acted upon by
a digestive juice. The dispersal of such plants is in the
first instance by wind, and in the second by animals which
further prepare them for germination.

(2) Birds sometimes carry seeds great distances in mud
adhering to their feet.

(3) Fruits and seeds form an important food for many
birds. They are attracted by the bright colours of fleshy
fruits, of which they eat the edible parts. Such fruits often
have either an indigestible, stony endocarp around the
seed, as in drupes like the Cherry and Brambles ; a hard
fruit-coat, as in the achenes of the Strawberry ; or, where
the endocarp is pulpy, as in berries, a hard seed-coat.
While the fleshy parts are digested, the protected seeds
often escape ; they may pass through the food-canal
of the bird, or be ejected in the pellet from the crop.
By these means they may be carried some distance from
the parent plant and be capable of germination. Thrushes
eating such fruits often pick off the fleshy part and by
a jerk of the head throw the stones away.

Many examples of fleshy fruits are found in the hedge-
rows, a fact which is especially interesting when we
remember how important hedgerows are as nesting-places

DISPERSAL OF FRUITS AND SEEDS 225

for birds. Fruits such as the following are commonly
to be found : Hawthorn, Rose, Blackberry, Raspberry,
Strawberry, Blackthorn, Plum, 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) Animals like the sheep and goat often have large
numbers of hooked fruits in their coats. Structures of this
kind which have become entangled in the wool are called

Fig. 160. Hooked Fruits. — i, Cleavers ; 2, 3, and 4, achenes
of Avens showing the bending of the style to form a hook; 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 the
wool is eventually scoured and these foreign bodies with
the dirt are thrown on to the waste-heaps near the factories
the 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, it will
be seen that the hooks are developed from different
organs (Fig. 160, 1-5).

In the Cleavers (Fig. 160, 1), Sanicle, and Enchanter's
Nightshade, they are on the fruit -coat. In the Avens
(Geum) the style is hooked (2, 3, 4). In the Burr Marigold

1296

226

THE REPRODUCTIVE ORGANS

they are barbed pappose bristles ; while those of the
Burdock (Fig. 160, 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 some
of these may be left, which then germinate.

(6) Again, ants are active agents in fruit and seed
dispersal, especially in the case of those seeds which have
oil-bodies attached to them. This is well seen in the Gorse
(Fig. 161, 1), and more clearly still in the Castor Oil seed
(2). Similar oil -bodies occur in many plants, e. g. Cow
Wheat, Cornflower, and several fruits of Sedges, Rushes,

1. 2.

Fig. 161. Seeds with Oil-bodies.
I, Gorse ; 2, Castor Oil ; 0, oil-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 be
observed if such seeds are laid in their track.

D. Propulsive mechanisms. — In addition to the modes
of dispersal already mentioned, many plants possess
devices which render them independent of wind, water, or
animals as carrying agents. (1) Often, as the fruit ripens and
dries, tensions are set up in the fruit-coat, which result
in a sudden bursting, whereupon the seeds are shot out
sometimes several feet.

DISPERSAL OF FRUITS AND SEEDS 227

(a) This is well observed in pods of Gorse, Broom, and
Sweet-Pea (Fig. 162, 1) ; (5) the two valves of the siliquas
of Crucifers, like Bitter Cress (2), split apart suddenly from
below upwards ; (c) in Violets (3) the capsule splits into
three valves ; then the edge of each closes over and presses
on the smooth pear-shaped seeds, which are then forcibly
ejected ; (d) in the Geranium (4) the five carpels separate
from below upwards, press against the calyx, and eventually

Fig. 162. Explosive Fruits. — 1, pod of Sweet-Pea ; 2, siliqua
of Bitter Cress; 3, capsule of Violet; 4, fruit of Geranium; 5,
hygroscopic fruit of Crane's-bill ; 6, twisted awn of Oat ; 7, capsule
of Wood Sorrel ; 8, Balsam or Touch-me-not.

gain sufficient force to spring away and throw out the seed
as from a sling ; (e) the Crane's-bills (5) split similarly; but
the long awn twists spirally and is jerked off, still retaining
the seed. This is buried by the movements of the awn,
which untwists when moist and coils up again when dry ;
(/) the awns of some Grasses act in a similar way (6). But
awns may straighten suddenly and jerk the grain some little
distance. Stiff hairs on the fruit-coat serve as anchors,
preventing the fruit from being drawn upwards from the
soil. Plants of this kind are able to bury their own seeds.

p 2

228 THE REPRODUCTIVE ORGANS

(2) The turgidity of part of the fruit-coat or seed is
the means of expelling many seeds. Interesting examples
to observe are the Wood Sorrel (7) and the Balsam (8). In
the former each seed has a fleshy aril, the inner layer of
which is very turgid. If the ripe fruit is disturbed, the
capsule splits, the aril suddenly turns inside out, and
the seeds are shot some distance. If the ripe fruits of the
Balsam are lightly pressed between the fingers, the fruit-
coat splits and the valves roll up inwards with great force,
scattering the seeds in all directions.

PART III

SYSTEMATIC BOTANY

CHAPTER XVIII
CLASSIFICATION OF PLANTS

In the preceding chapters we have investigated the
structures and functions of the organs which constitute a
plant ; the development of plants ; and their perpetuation.
In the course of our study we have met with many indi-
viduals, and occasionally analogies and differences have
been pointed out. But, so far, no general attempt has
been made to classify and arrange the two hundred thou-
sand 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.

History of systematic botany. — There is little doubt that
in the early dawn of civilization the culture of plants was
studied from the utilitarian point of view : by the agri-
culturist to provide food for himself and his flocks and
herds, and by the physician to prepare useful 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

230 SYSTEMATIC BOTANY

during preceding centuries. But beyond the subdivision
by Aristotle and Theophrastus into Trees, Shrubs, and
Herbs, this branch of our science was practically dormant
until the sixteenth century.

The beginning of a scientific system is indicated in the
celebrated Herbal of John Gerard, but to better advantage
in the De Plantis of Andreas Caesalpinus, who divided the
vegetable kingdom into fifteen classes, each distinguished
by a typical fruit. Other distinguishing characters were
introduced by subsequent writers. John Ray divided
' flowering ' from ' flowerless ' plants, and suggested the
terms Monocotyledons and Dicotyledons as prime divisions
of the former. Robert Morison considered the structures
of the flower and of the fruit ; and De Tournefort proceeded
to more detail by taking the corolla into account.

The illustrious Swedish botanist, Carl Linne, better
known by the latinized form of his name, Linnaeus, now
enters into our brief review. He introduced a classification
based upon the reproductive organs, i. e. the stamens and
pistil. 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 author
was aware that these considerations were essential to a
correct classification of the vegetable kingdom. It fore-
shadowed a natural system, a system which would exhibit
a continuous sequence of plant-life, from the lowest vege-
table organisms to the most elaborated members of the
plant world. Such a system could not be derived from
a study of the functions and forms of one or more special
organs of plants ; it could only be deduced from a study
of the forms and development of these organs.

CLASSIFICATION OF PLANTS 231

In the construction of natural systems, the earliest
pioneers were the French botanists De Jussieu and De
Candolle. Robert Brown and John Lindley in England,
and Endlicher in Germany, added much to our knowledge.
Later Bentham and Hooker in England, also Eichler and
Engler in Germany, materially advanced the natural system.
The history and development of botanical classification
can be studied in Sachs's History of Botany. The foregoing
account sufficiently acquaints the student with the follow-
ing important fact :

A means of classification is to be sought only in the study
of the form, function, and development of the organs which
constitute plants.

Concurrently with the advance in botanical classifica-
tion, or Systematic Botany, nomenclature received much
attention. The binomial system gradually supplanted all
others, in which every plant received a compound name,
the first representing its genus and the second its species ;
and in the case of closely-related forms a third or varietal
name was added. Groups of related genera form an order ;
of related orders, a cohort ; and of related cohorts, a. family
or class.1

The chief divisions of flowering plants. — A brief summary
of the characters of the larger groups will illustrate the use
made of the parts of the flower and fruit in classifying
plants. All plants which produce seeds, e. g. Pine, Larch,
Buttercup, Stock, Primrose, Daisy, Bluebell, and Crocus,
belong to one large group, the Spermaphyta (Gr. sperma
= a seed, phyton = a plant), and are thus distinguished
from such plants as Algae, Fungi, Mosses, and Ferns,
which do not produce seeds.

Cone-bearing plants like the Pine and Larch produce
naked ovules : that is, the ovules are not enclosed in an

1 In some systems of classification the term family is used instead
of order, and the latter term takes the place of cohort.

233 SYSTEMATIC BOTANY

ovary before pollination. Such seed-plants are included
in 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 Angiosperms
(Gr. angeion = a vessel) ; to this group belong the great
majority of the seed-plants of the vegetation of the present
day. 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 Dicotyle-
dons. On the other hand, the parts of the flowers of the
Bluebell and Crocus are in threes, and the embryo of the
seed has only one cotyledon. Such Angiosperms form the
class Monocotyledons.

These classes are further subdivided according to the
relationships of the parts of the flower. Dicotyledons
with a simple perianth of free petals in one or two whorls
are known as Archichlamydeae (Gr. arche = beginning,
chlamys = a mantle), while those with a more highly
developed perianth, in two whorls, the petals being joined
together by their edges to form a gamopetalous corolla,
are called Metachlamydeae (Gr. meta = beyond) or Sym-
petalae (Gr. syn = together).

Other subdivisions depend on (i) the relations between
stamens and pistil, whether the former are hypogynous,
perigynous, or epigynous ; and (2) the condition of the
ovary, whether apocarpous or syncarpous — one or more
celled.

We thus see that the characters of most importance in
classification are those to be noticed in a careful examina-
tion of the parts of a flower from outside inwards. The
classification of the above-mentioned plants may be shown
as follows :

CLASSIFICATION OF PLANTS 233

Spermaphyta

Gymnosperms Angiosperms

Dicotyledons Monocotyledons

1 i

Archichlamydeae Sympetalae

I I

apocarpous superior superior

I I I
Pine Buttercup Primrose Bluebell

Larch |

syncarpous inferior inferior

I I I

Stock Daisy Crocus

The Study of a local flora. —A book dealing with the plants
of a country or a district, in which the species are arranged
and classified in the manner indicated, is called a Flora.
In the study of the vegetation of your district you will find
it 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 view and follow
it with care and intelligence. In each habitat probably one
or only a few species, which are best adapted to it, 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 sturdy
trees and shrubs and the plants growing under their shade
and protection.

Note in detail the form, mode of growth, and the struc-
ture of the leaf, and see whether these bear any relation
to 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-
societies and associations according to the conditions
of the habitat (Fig. 163).

234 SYSTEMATIC BOTANY

By means of a Flora determine the species carefully and
try to arrange the plants found in the order of importance
in the vegetation : first the dominant ones, then the fre-
quent and occasional ones, and so on in descending order.
A collection of the characteristic species should be made
and classified according to habitat. Each should bear
a label giving the following particulars : natural order,
genus, species, plant-association or society, position in the
association (i. e. dominant or otherwise), locality, 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 more
interesting facts concerning their distribution.

CHAPTER XIX
CLASS I, DICOTYLEDONS

Archichlamydeae

Dicotyledons are distinguished by having the vascular
bundles of the stem arranged in a ring, the leaves are
net-veined, the parts of the flower are in whorls of four
or five, and the embryo of the seed has two cotyledons.

This class is much larger than that of the Monocotyle-
dons. The broad, net-veined leaf is very characteristic ;
secondary thickening is general. Dicotyledonous trees
form the great deciduous forests of Temperate regions ;
the evergreen shrubs and peculiar xerophytes of semi-
desert and desert regions belong largely to this class,
and many of the species forming the rank vegetation of
Tropical forests are also Dicotyledons.

Q
O
O

w
o

Q
W

p
«:
w

I/)

23+

DICOTYLEDONS : ARCHICHLAMYDEAE 235

The Dicotyledons are divided into two great divisions.
The first, Archichlamydeae, includes plants which have
a relatively simple type of flower. The natural orders of
this division embrace flowers increasing in complexity
from primitive forms like Willows and Buttercups, with
many stamens and much pollen, up to the more highly
specialized forms like the Sweet-Pea and Violet, or, as in
the Hogweed and Chervil, to small epigynous flowers
rendered attractive by being massed into compact inflo-
rescences. The second division, Metachlamydeae, is charac-
terized by the petals being joined into a flower-tube, as
in the Heath and Primrose, 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 division.

(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 petals 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 have
two carpels in the axil of a bract ; syncarpous ; ovules
indefinite. Fruit a capsule. Seeds with a tuft of
hairs at the base (see Fig. 185, p. 278).

The Willows, Sallows, and Osiers are abundant in the
North Temperate region, especially in low-lying, wet
areas. Many are pollarded (Salix alba, &c.) ; others are
coppiced (S. viminalis), and used for basket-making
(see p. 277). On mountains in Britain, in the Alps, and in
Arctic regions, very small creeping forms occur, only one
or two inches high, e. g. Salix herbacea and S. reticulata.

236 SYSTEMATIC BOTANY

The Poplars (Populus) also belong to this order (see Fig.
186).

Order Betulaceae.1 Shrubs or trees with simple
stipulate leaves. Flowers in terminal catkins. Monoe-
cious, and usually arranged in small three-flowered
cymes in the axils of the bracts of the catkin (Fig. 188).
Perianth reduced. Ovary inferior ; carpels two, syn-
carpous, two-celled, one ovule in each cell. Fruit a one-
seeded indehiscent nut.
This order includes several well-known trees, e. g. Birch
(Betula alba), Alder (Alnus glutinosa), Hazel (Corylus
Avellana), and Hornbeam (Carpinus Betulus) (see Figs. 187,
188, 189, pp. 282-7).

Order Fagaceae.1 Trees with simple stipulate leaves.

Flowers in axillary catkins, monoecious. Perianth

lobes 5-6. Carpels three, syncarpous. Ovary inferior,

usually three-celled with two ovules in each. Fruit

a one-seeded nut. Nuts enclosed in a cupule (see

Fig. 191, p. 290).

The order includes many forest trees, e. g. Oaks (Quercus

spp.2), Beech (Fagus sylvatica), and Sweet Chestnut (Cas-

tanea sativa).

Order Ranunculaceae. The perianth is indefinite, often
petaloid and polypetalous. Stamens indefinite and
hypogynous. Pistil superior. Carpels indefinite and
usually apocarpous. Fruit a group of achenes or
follicles (Figs. 144 and 149). The flowers may be
cyclic: Aquilegia; hemicyclic : Ranunculus; acyclic
or spiral : Aconitum, Helleborus.

The plants of this order are chiefly North Temperate,

1 The orders Betulaceae and Fagaceae are very closely related,
and sometimes placed in one order, Cupuliferae.

2 Spp. after a generic name means there are several species in
■the genus.

DICOTYLEDONS : ARCHICHLAMYDEAE 237

and many occur in Britain, where they are often cultivated
for their showy flowers. There is great diversity in the
flowers ; the perianth is often petaloid without differentia-
tion into calyx and corolla. The following should be
examined and their peculiarities noted : Meadow Rue
{Thalidrum), with small flowers and inconspicuous perianth,
Clematis (Fig. 109, p. 164), Anemone (Fig. no, p. 164), Marsh
Marigold (Fig. in, p. 164), and Christmas Rose (Helleborus),

Fig. 164. Floral Diagram of Buttercup.
a, stamens ; br, bract ; c, carpels ; ca, sepals ; p, petals.

with a petaloid calyx and no corolla, except in the latter.
In Caltha, honey is secreted by the carpels, and in the
Christmas Rose by small, tubular ' petals '. In the Butter-
.cups (Fig. 112, p. 166) {Ranunculus spp.) there is a calyx
and a conspicuous corolla, and the nectary is at the base
of the petals. In the Columbine (Fig. 130, 1, p. 186)
(Aquilegia vulgaris) the five petals form long, honey-secreting
spurs. In the Larkspur (Fig. 130, 3-5, p. 188) {Delphinium),
the spurred posterior sepal contains the two posterior honey-
secreting petals. In the Monkshood (Fig. 130, 2, p. 187)
[Aconitum Napellus) the posterior sepals form a large, blue

238 SYSTEMATIC BOTANY

hood, enclosing two nectaries, which are modified petals.
In the two latter the flowers are zygomorphic. Floral for-
mula : k 5 or 3, c 0-5 or 00, a 5- 00, gi-oo.

The nectaries of the Christmas Rose, Winter Aconite
(Eranthis), Love-in-a-Mist (Nigella), Monkshood, and Aconite
are 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 four
inner long ones (tetradynamous). Pistil superior of
two carpels (syncarpous), two-celled, divided by
a partition (replum). Fruit, a siliqua or silicula
(Figs. 1-5).

This order contains upwards of 200 genera and 1,200
species widely distributed throughout the North Temperate
and Mediterranean regions. They are mostly herbaceous
perennials, but some are annuals, and others are biennials.
The leaves are without stipules ; the inflorescence is
a raceme or corymb, and is usually without bracts.

Very many cultivated plants belong to this order, e. g.
the Cabbage (Brassica oleracea), from which many useful
varieties have been derived by cultivation and selection,
such as Red Cabbage, Kale, Savoy, Brussels Sprouts, in
which the axillary buds become small cabbages. In the
Broccoli and Cauliflower the inflorescence becomes abnor-
mally branched and fleshy, and the Kohlrabi is a tuberous
stem or corm.

From other species of Brassica are derived the Turnip
and Swede ; the Radish, Horse-Radish, Watercress,
Garden Cress, and Mustard, also belong to this order, as
well as some of the commonest weeds of cultivation, e. g.
Charlock and Shepherd's Purse ; while others are culti-
vated for their flowers, for example, Wallflower, Stock,
Candytuft, Honesty, Arabis, and Aubretia.

DICOTYLEDONS: ARCHICHLAMYDEAE 239

Order Caryophyllaceae. Herbs with opposite leaves,
nodes swollen, inflorescence a dichasium or scorpioid
cyme. Flowers regular. Sepals 4-5. Petals 4-5,
usually white or pink. Stamens 8-10, the outer
whorl usually opposite the petals, hypogynous or
sometimes perigynous. Pistil 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 familiar
plants, both wild and cultivated. Many species occur in
Britain in very varied habitats, as often suggested by their
common names, e. g. :

Water Chickweed (Stellaria aquatica), Bog Stitchwort (S. uli-
ginosa). On the coast we have: Sea Campion {Silene maritima),
Sea Purslane (Arenaria peploides), Sea Spurrey (Spergularia rupe-
stris), Sea Pearlwort (Sagina maritima). On the mountains: Sea
Campion (Silene maritima) , and alpine species of Chickweed (Cera-
stium alpinum), Moss Campion (Silene acaulis), Alpine Campion
(Lychnis alpina), Pearlwort (Sagina spp.). On walls, rocks, dry
banks, and fields : Pinks and Carnations (Dianthus spp.), Chickweeds,
Sandworts and Pearlworts.

In moist woods and hedgebanks : Red Campion (Lychnis dioica),
Ragged Robin (L. Flos-cuculi) , Greater Stitchwort (Stellaria Holo-
stea), Wood Stitchwort (S. nemorum). As weeds of cultivation :
Bladder Campion (Silene inflata), Corn Cockle (Lychnis Githago),
Chickweeds (Stellaria media, Sec), Corn Spurrey (Spergula arvensis).

Many plants of this order are readily distinguished by
their opposite, entire leaves and swollen nodes, and also
by the inflorescence, which is very characteristic. The
main axis ends in a flower (Fig. 165, 2). 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 process may be repeated.
The name dichasium or false dichotomy is given to
this type of inflorescence. Sometimes one of the branches
at a node outgrows the other, and in the later branches

240

SYSTEMATIC BOTANY

X 2

Fig. 165. 1, Floral Diagram of Lychnis ; 2, Inflorescence
of Cerastium ; 3, Diagram of a Monochasial Cyme ; 4, Ver-
tical Section of Male Flower of Red Campion ; 5, Vertical
Section of Female Flower of Red Campion ; 6, Fruit of
Dianthus ; an, androphore ; br, bract ; c, calyx ; co, corona ;
/, teeth of capsule.

DICOTYLEDONS : ARCHICHLAMYDEAE 241

one only is developed, the bud in the axil of the other
leaf being suppressed, and giving origin to a monochasial
cyme or cincinnus (Fig. 165, 3). The flower is typically
pentamerous, i. e. its parts are in whorls of five each, and
the floral formula is K5, 05, a 5 + 5, g (i).

Many modifications, however, are met with, and the
plants of the order may be divided into two groups :
(1) A higher group which includes the Pinks, Catchflys,
and Campions, and (2) a lower group in which are the
Stitchworts, Chickweeds, &c.

The floral diagram of a Campion (Lychnis) is shown in
Fig. 165, 1. Note that the stamens of the innermost whorl
are opposite the sepals, and the outermost whorl stands
opposite the petals. This arrangement (also found in the
Wood Sorrel) is said to be obdiplostemonous (L. ob =
inverse, Gr. diploos = double, stemon = a. filament). The
outer stamens are formed first, and ripen before the inner
ones.

Cut a flower vertically, and note the arrangements of
its parts. The five sepals are united to form a tube (gamo-
sepalous), the internode between the calyx and corolla
has elongated and raised the corolla, stamens, and carpels
on a stalk (androphore) (Fig. 165, 4 and 5). The corolla
has five free petals, the limb often divided. In the Red
Campion there is an outgrowth at the junction of limb
and claw of each petal, forming together a corona (Fig.
165, 4 and 5, co).

Note the arrangement of the ten stamens. The anthers
are ripe before the stigmas (proterandrous) . Look for the
nectary at the bases of the stamens. The pistil has five styles,
the ovary consists of five carpels, syncarpous, and one-celled.
(In Silene there are only three carpels.) Cut transverse and
longitudinal sections of the ovary and note the free-central
placenta on which are numerous ovules. The gamosepalous
calyx and long, narrow flower-tube exclude all but the long-

1296 Q

242 SYSTEMATIC BOTANY

tongued insects, such as bees, moths, and butterflies. The
fruit is a capsule opening by four to ten teeth (Fig. 165, 6),
and the seeds, ornamented with wart-like outgrowths,
are dispersed by wind or animals (see p. 222).

The Red Campion (L. dioica) is dioecious ; the female
plant also differs from the male plant by its larger size
and coarser growth. Some species with white flowers,
e. g. Night-flowering Campion (Silene noctiflora), are closed
during the day, but are open and sweet-scented at night,
and are visited by night-flying moths.

The flower-stalks of the Catchfly are covered with sticky
hairs, 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 pollinate
themselves. Sometimes the petals are so deeply cleft that
the corolla appears to have eight or ten petals. In the
Stitchworts, Pearlworts, and others, we often meet with
reduced flowers

Order Rosaceae. Leaves usually stipulate, receptacle
more or less hollowed, sepals and petals four or five
each, stamens indefinite, perigynous, ovary usually
superior and apocarpous (Fig. 166, 1) ; sometimes (e.g.
Apple) it is inferior and syncarpous (2).

There are ninety genera and upwards of two thousand
species in this widely distributed order. It contains many
familiar and cultivated species, including a large number
of our common fruit trees and shrubs. Many spread
rapidly by vegetative reproduction, e. g. the Strawberry,
Silverweed, and the Blackberry by runners, and the Rasp-
berry by suckers (Fig. 27, p. 61).

The flowers resemble those of Ranunculaceae, but are

DICOTYLEDONS : ARCHICHLAMYDEAE 243

distinguished from them by the hollow or concave recep-
tacle, perigynous calyx, corolla, and stamens, and by the
fact that these parts of the flower are in whorls and not
spirally arranged. The form of the receptacle and the
mode of origin and structure of the fruits of this order
are interesting ; and the following should be studied as
showing transitions from perigynous to epigynous, and
apocarpous to syncarpous flowers and fruits. The Meadow-
sweet {Spirea Ulmaria) has a nearly flat receptacle ; the fruit

Fig. 166.
1, Floral Diagram of Plum ; 2, Floral Diagram of Apple.

is a group (aeterio) of two-seeded, twisted follicles. The
Tormentil (Potentilla 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
(Fragaria vesca) has an epicalyx (Fig. 113, 1), and the central
convex part of the receptacle enlarges in the fruit, becomes
fleshy, and bears the dry achenes on the outside of it.
The Blackberry (Rubus fruticosus) 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

244 SYSTEMATIC BOTANY

(see Fig. 153). The achenes of the Mountain Avens (Dry as
octopetala) have a persistent feathery style for wind-dis-
persal ; and in the Water Avens (Geum rivale) the style
becomes hooked and the fruit is dispersed by the fur of
animals (Fig. 160, 2,3,4). The Lady's Mantle (Alchemilla
vulgaris) has very small, 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 dry
hollow receptacle. The Salad Burnet (Poterium Sangui-
sorba) has no corolla, the flowers are monoecious and
crowded into a head, the upper ones are female with
feathery stigmas, the lower ones are male with many
stamens, 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. 146).
In the Apple (Pyrus Malus) the five carpels are syncarpous
and inferior, and united to the fleshy receptacle (Fig. 155).
Other familiar pome fruits are Pear (Pyrus communis),
Quince (Cydonia vulgaris), Cotoneaster, Rowan (Pyrus
Aucuparia), and Hawthorn (Crataegus Oxyacantha).

Thus we get development from perigyny to epigyny
in Meadowsweet, Tormentil, Blackberry, Rose, Cherry,
Apple, and Pear ; from apocarpy to syncarpy in Meadow-
sweet, Tormentil, Blackberry, Cherry, Apple, and Pear ;
and fruits of special interest in Avens, Rose, Strawberry,
Blackberry, Cherry, and Apple (see pp. 217-19 and 225).

Order Papilionaceae (Leguminosae). Leaves stipu-
late, flowers in racemes, papilionaceous. Stamens ten,
perigynous, united into a tube by their filaments
(monadelphous) or nine united and one free (diadel-
phous). Pistil of one carpel, superior, apocarpous.
Fruit a legume (Fig. 167).

Papilionaceae is a sub-order of Leguminosae. In the
latter order are included such species as the Acacias, the

DICOTYLEDONS : ARCHICHLAMYDEAE 245

Sensitive Plant, Judas-tree, and Divi-divi. It is one of the
largest orders of flowering plants and contains 440 genera
and upwards of 7,000 species. All the British species have
papilionaceous flowers, and belong to the above sub-order.
Many species have nodules on their roots, by means of which
the plants can utilize atmospheric nitrogen and thrive in
soil deficient in nitrates. Many are climbers : the Scarlet-
Runner and Kidney Bean have twining stems, but many
climb by means of leaf -tendrils. Some are xerophytes

Fig. 167. Floral Diagram of Sweet-Pea.

with leaves reduced to phyllodes, as in some Acacias
(Fig. 96, 1), or the leaves are small and the stems angular
and green, as in the Gorse and Broom. The stipules are
often large, and in some cases — e. g. in the Yellow
Vetchling {Lathyrus Aphaca) — they perform the functions
of leaves, the remainder of the blade being transformed
into tendrils.

The leaflets usually perform sleep-movements, and direct
the edges of the leaflets to the sky, some assuming the sleep-
position immediately when touched, e. g. the leaves of the
Sensitive Plant (Mimosa pudica). The flowers are adapted

246 SYSTEMATIC BOTANY

to pollination by bees (see p. i88, where a full description
of a papilionaceous flower will be found) ; a few are self-
pollinated, e. g. Edible Pea (Pisum sativum), and species
of Vetch (Vicia), some of which have cleistogamous flowers.
In the Gorse (Ulex europaeus) (Fig. 133), the Petty Whin
(Genista anglica), Laburnum (Cytisus Laburnum) (Fig. 201),
Rest-harrow (Ononis arvensis), and Lupin (Lupinus spp.),
the stamens are monadelphous, and the flowers have
no honey, although the Broom has ' honey-guide? '. In
others the stamens are diadelphous, e. g. Clover (Trifolium
spp.), Bird's-foot Trefoil (Lotus corniculatus) , Vetches and
Tares (Vicia spp.), Pea, Bean (Vicia Faba), Scarlet-Runner
(Phaseolus multiflorus) , and Sweet Pea (Lathyrus odoratus)
(Fig. 131). 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
Sainfoin. The Groundnut or Peanut (Arachis hypogaea)
develops its pods underground.

Order Umbelliferae. Flowers usually 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 honey-
secreting disk. Fruit a cremocarp, which splits
into two half-fruits (mericarps) (Fig. 148).

This order is remarkable in having small flowers
massed 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. 119
and 244). Many of the species are poisonous, e. g. Hem-
lock (Conium macidatum) ; others, like the Carrot (Daucus
Carota) and Parsnip (Peucedanum sativum), are edible, and
largely cultivated for their fleshy roots. In the Celery

DICOTYLEDONS : ARCHICHLAMYDEAE 247

(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 Petro-
selinum), Caraway ' seeds ' (the fruits of Carum Carui),
Aniseed (the fruits of Pimpinella Anisiim), and Coriander
' seeds ' (the fruits of Conundrum sativum). Samphire
(Crithmum maritimum) and Fennel (Foeniculum vulgare)
occur on sea cliffs, and the Sea Holly (Eryngium maritimum)
on sandy shores. Some, like the Chervil {Chaerophyllum

Fig. 168. Floral Diagram of Heracleum.

sylvestre), are troublesome weeds in meadows. Several
species are marsh plants, e. g. Marsh Pennywort (Hydro-
cotyle vulgaris), Wild Celery (Apium graveolens) , Dropworts
(Oenanthe spp). On stream-sides occurs Sweet Cicely
(Myrrhis odorata), and several are common in fields and
hedgebanks, e. g. Fool's Parsley (Aethusa Cynapium),
Hogweed {Heracleum Sphondylium) , Earth-nut (Cono-
podium denudatum), and Hedge Parsley (Caucalis An-
thriscus).

Usually the fruits consist of two flattened mericarps,

248 SYSTEMATIC BOTANY

and are dispersed by the wind (see Fig. 148, p. 214). In
the Wood Sanicle (Sanicula europaea) the fruits are hooked
and dispersed by animals.

The Archichlamydeae includes upwards of sixty thousand
species. The more primitive forms are distinguished from
the 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 spirally
arranged 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. In
the Umbelliferae many small irregular epigynous flowers
are massed together in conspicuous umbels. The division
is 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 is in two whorls, and the
petals are united (gamopetalous).

Order Primulaceae. Flowers often on scapes, usually
regular. Sepals five. Petals five, united. Stamens
five, epipetalous and opposite the petals. Ovary

DICOTYLEDONS : METACHLAMYDEAE 249

superior, syncarpous, one-celled with a free-central
placenta. Fruit a capsule, splitting into five valves
(Fig. 169).

The plants of this order are mostly perennials with
rhizomes or corms. The inflorescence is often a scape,
and in the Cowslip {Primula veris) the flowers are in a simple
umbel (Fig. 121, 2). In the Primrose (P. vulgaris) the
scape is very short and the flowers appear to arise singly
from the short stem (Fig. 121, 1). The flowers are often

Fig. 169. Floral Diagram of Primrose.

heterostyled (see p. 177) in Primula, Water Violet {Hot-
tonia palustris), and Sea Milkwort (Glaux maritima). The
five stamens are opposite the petals (antipetalous), and
the five outer stamens are suppressed. In the Brook-weed
(Samolus Valerandi) the outer whorl of stamens is repre-
sented by five staminodes. The petals of Cyclamen are
strongly reflexed. It is not easy to determine the five
carpels of the pistil, but the capsule usually splits into five
valves, and sometimes abnormal flowers produce five
leaves in place of the pistil.

250 SYSTEMATIC BOTANY

Many species flower in the early spring, and are common
on the mountains. Rosette-forming species are frequent,
Alpine forms like Androsace form compact cushions, and
the little Soldanellas send up their flowers through the
snow. Many grow in wet places, e. g. Brook- weed, Loose-
strife (Lysimachia) , Creeping Jenny (L. Nummularia), and
the Bog Pimpernel (Anagallis tenella), which occurs in
peaty bogs. The Water Violet is an aquatic plant with
finely divided leaves which hibernates by means of winter
buds. The Scarlet Pimpernel (A. arvensis) is a cornfield
weed, and the Sea Milkwort occurs in salt-marshes. The
Chickweed Wintergreen (Trientalis) grows in heaths and
upland heathy woods.

Order Boraginaceae. Mostly herbs with alternate
exstipulate leaves ; usually rough with hairs. Flowers
often showy in single or double scorpioid cymes
which are coiled when in bud ; the flowers as they
open all face the same way (Fig. 170, 1). Calyx five-
lobed. Corolla regular, hypogynous, tubular, lobes
five, often spreading ; throat more or less closed by
projecting scales or hairs. Stamens five, epipetalous.
Pistil of two carpels, style gynobasic (Fig. 170, 2).
Fruit four one-seeded nutlets (Fig. 171).

The more familiar species are : Forget-me-nots (Myosotis spp.),
Comfrey {Symphytum officinale), Borage (Borago officinalis),
Evergreen Alkanet (Anchusa sempervirens) , Hound's-tongue
(Cynoglossum officinale), Lungwort (Pulmonaria officinalis),
Viper's Bugloss (Echium vulgare).

The flowers of most species show interesting colour-
changes during their development, as suggested by the
name of one of the Forget-me-nots (Myosotis versicolor),
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, changing

DICOTYLEDONS : METACHLAMYDEAE 25 r

later to violet and blue. The flowers are visited by flies,
bees, and moths, and the honey is protected by the narrow
tube and overhanging scales or hairs.

Borage and Comfrey are typical bee-flowers. They are

Fig. 171. Floral Diagram of
Forget-me-not.

Fig. 170. Forget-me-not. — 1, in-
florescence; 2, pistil ; 3, vertical section
of flower ; co, corona.

pendulous, and the cone of stamens showers pollen on the
head of the visiting bee in a manner similar to that of the
Heaths. The Lungworts have dimorphic flowers, with
long and short styles, as in the Primrose, and the corolla-

252 SYSTEMATIC BOTANY

tube is closed by five tufts of hairs between the stamens.
The fruit of the Hound's-tongue is provided with recurved
hooks, as is also the calyx of the Forget-me-not, which
serve as a means of fruit-dispersal by animals.

Order Tabiatae. Stem square ; leaves opposite ; flower
zygomorphic. Sepals five, united. Petals five, united,
two-lipped. Stamens usually four, two long and two
short (didynamous), epipetalous. Pistil of two carpels,
superior, syncarpous, each carpel divided into two cells.
Ovary four-lobed, with the style springing from the
base (gynobasic). Fruit usually four nutlets (Fig. 172) .

There are about 150 genera and 2,800 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, hairy leaves. Many
are scented, due to volatile oils secreted by epidermal
glands, and are often cultivated and used as condiments,
or for their oils or perfumes, e. g. Lavender (Lavendula
vera), Rosemary (Rosmarinus officinalis), Thyme (Thymus
vulgaris), Mint (Mentha viridis), Peppermint (M. piperita),
Marjoram (Origanum vulgar e), Garden Sage (Salvia offici-
nalis).

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 the
leaf-axils, give rise to false whorls of flowers called verti-
cillasters (Fig. 172, 2). The flowers are adapted chiefly to
bees (Fig. 172, 3), and some to moths and butterflies. The
simpler flowers with shorter tubes, e. g. Thyme and Gipsy-
wort, are visited by miscellaneous insects. The Henbit-
Deadnettle (Lamium amplexicaule) produces cleistogamous
flowers.

Fig. 172. Deadnettle. — 1, floral diagram ; 2, inflorescence
3, flower in vertical section.

254 SYSTEMATIC BOTANY

Many species may be found in pastures, meadows, and
hedgerows in Britain, e.g.:

Ground Ivy (Nepeta hederacea), Self-heal (Prunella vulgaris).
Hedge Woundwort (Stachys sylvatica), Wood Betony (5. officinalis),
White Deadnettle (Lamium album), Red Deadnettle (L. purpureum),
Yellow Archangel (L. Galeobdolon), Wood Sage (Teucrium Scoro-
donia), Bugle (Ajuga reptans).

Some are common cornfield weeds, e. g. Hemp Nettle (Galeopsis
Tetrahit), Corn Mint (Mentha arvensis).

Others are marsh plants, e. g. Marsh Woundwort or Water Mint
\M. aquatica), Greater Skullcap (Scutellaria galericulata) , Gipsy-
wort (Lycopus europaeus).

Order Solanaceae. Flowers usually regular. Sepals
five, united. Petals five, united. Stamens five, epi-
petalous ; antheis often united. Carpels two, syncar-
pous, and placed obliquely. Ovary two-celled, ovules
indefinite ; style terminal. Fruit a capsule (e. g.
Henbane), or a berry (e. g. Bittersweet and Potato)
(Fig. 173).

The leaves are alternate, but in the inflorescence, as a
result of fusion and displacement (adnation), two leaves
occur apparently at the same node. The flowers are
usually regular, but a few are zygomorphic, and form a
transition to the order Scrophulariaceae.

Only four species grow wild in Britain, one of which, the
Woody Nightshade (Solatium Dulcamara) (Fig. 125), is
common in hedgerows, but many are familiar in cultivation.
A large number occur in Central and South America, from
whence we have obtained such plants as the Potato (Sola-
rium tuberosum), Petunia, Winter Cherry (Physalis spp.),
and Tobacco (Nicotiana Tabacum). The flower of the
Tobacco has a very long corolla-tube, and is 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 the
plants after which they have been named, namely Atropa
Belladonna (Deadly Nightshade), Nicotiana 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 Stramonium).

The ' Tea-tree ' (Lycium chinense) is frequent in hedge-
rows but, unlike the Bittersweet, is not a native of Britain.

Fig. 173. Floral Diagram of Woody Nightshade.

Cayenne pepper is obtained from pods of species of
Capsicum. Some fruits are edible, e. g. Tomato (Solanum
Lycopersicum). The Mandrake (Mandr agora officinalis),
connected with which are so many strange superstitions,
also belongs to this order.

Order Scrophulariaceae. Flowers zygomorphic, very
variable ; sepals five, united. Petals five, united, often
two-lipped. Stamens four, two long and two short
(didynamous), sometimes only two, epipetalous. Pistil
of two carpels, superior, syncarpous. Ovary two-celled,
style terminal (Fig. 174).

256 SYSTEMATIC BOTANY

This order contains many poisonous species and is closely
related to Solanaceae, but usually the flowers are irregular
and the ovary is not oblique. Many species occur in
Britain, and they possess interesting peculiarities both in
vegetative and reproductive organs. Several are semi-para-
sites (see pp. 358-9), e.g. species of Eyebright {Euphrasia
spp), Bartsia, Lousewort (Pedicularis spp), Yellow Rattle
(Rhinanthus spp.), and Cow- wheat (M dampy rum spp).

The Speedwells {Veronica) occur in varied habitats.
The Water Speedwell {V. Anagallis), Marsh Speedwell
(V. scutellata), and Brooklime {V. Beccabunga) are marsh or
aquatic. Several species are common cornfield weeds ;
while the Germander Speedwell {V. Chamaedrys) is common
on hedge-banks ; and others occur on heaths and moun-
tains. In gardens many New Zealand shrubby species
are cultivated, which are curious xerophytes with small
compact leathery leaves resembling species of Cypress, Box,
and other evergreens.

Other common species are Toadflax {Linaria spp.), Snap-
dragon {Antirrhinum spp.) (Fig. 174, 4, 5), Figwort {Scrophu-
laria spp.), Foxglove {Digitalis purpurea) (Fig. 174, 6), Musk,
and Monkey Flower {Mimulus spp), the latter having
sensitive stigmadobes 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 pollination, turn away, and the flower- stalk grows
and presses the fruits into crannies where they ripen and
shed their seeds. The Figworts are pollinated by wasps.
The stigma ripens before the anthers, and the stamens and
style lie on the lower lip of the flower.

The following flowers should be compared as to number
and position of stamens : Mullein {Verbascum Thapsus),
five stamens (Fig. 174, 1) ; Figwort and Pentstemon, four
stamens and a staminode ; Toadflax, Snapdragon, and

DICOTYLEDONS : METACHLAMYDEAE 257

Fig. 1 74. 1 , Floral Diagram of Verbascum ; 2, Floral Diagram
of Foxglove; 3, Floral Diagram of Speedwell; 4, Flower
of Snapdragon ; 5, Vertical Section of same ; 6, Vertical
Section of Flower of Foxglove.

1296

258 SYSTEMATIC BOTANY

Foxglove (Fig. 174, 2), four stamens and sometimes a
staminode in the two former. Veronica has only two
stamens (Fig. 174, 3 and Fig. 126).

Order Caprifoliaceae. Mostly shrubs or trees, leaves
decussate, usually exstipulate. Flowers in cymes,
regular, sometimes irregular, usually showy, epigynous.
Calyx five- toothed. Corolla five-lobed. Stamens five
(or four to ten), epipetalous. Carpels two to five,
syncarpous. Ovary inferior, one- to five-celled, with one
to many ovules in each cell. Fruit usually a berry or
a drupe (Fig. 175, 1).

This order includes a number of shrubs well known in
cultivation, several of which are found wild in Britain, e. g.
Elder {Sambucus nigra), Guelder Rose {Viburnum Opulus),
Wayfaring Tree {V. Lantana), Honeysuckle or Woodbine
{Lonicera Periclymenum) , the Snowberry {Symphoricarpus
racemosus), Weigelia {Diervilla florida) . Several others are
common in shrubberies.

The Elder has compound, pinnate, and stipulate leaves ;
small regular hermaphrodite flowers in umbellate cymes ;
and the fruit is a drupe with one to five stones.

The Guelder Rose has simple leaves with small glandular
stipules, and cup-like extra floral nectaries on the leaf-stalk
(Fig. 219, 5). The flowers are in corymbose cymes and
show an interesting division of labour (Fig. 175, 2). The
outer flowers of the inflorescence are neuter, with large,
attractive, irregular corollas ; but they have neither
stamens nor pistil (Fig. 175, 3). The inner flowers are much
smaller and perfect (Fig. 175, 4 and 5), producing bright
red drupe-like fruits each with one stone. In the cultivated
form of Guelder Rose all the flowers are neuter and have
large corollas.

The Wayfaring Tree is a characteristic shrub of the
woodlands on calcareous soil. The young shoots are

Fig. 175. Guelder Rose. — 1, floral diagram; 2, portion of
inflorescence ; 3, neuter flower ; 4, perfect flower ; 5, vertical
section of same.

. .'?_--: -i srir ~:?..~e _: : : : r : z'~-:~.-z:r :__t:

! 7^n~r —;.;■- -„-.-_ e~«~ ze

rTl-_ t-_: Irrl

' ~ - "._ " - 1 _ I - :~ _Z. .: 1 : : 1 : ~ .

■ - " .

■ ■

->' — i — , " --

- : "
: - :

■ - -

:v^-r

- :

- ™

-ts

■

i. i_

262 SYSTEMATIC BOTANY

The characteristic feature of the order is the highly
specialized inflorescence ; many small flowers being con-
densed into a conspicuous head or capitulum. Division of
labour is so well developed that a capitulum resembles
a single flower (see p. 155, Fig. 104), and the arrangements
for pollination by insects and dispersal of the pappose fruits
by the wind, are so perfect that the flowers represent the
highest stage of development yet reached by flowering plants.

The order is divided into two main groups :

(1) Tubuliflorae. — Plants without milky latex and the
florets of the disk tubular, not strap-shaped, e. g. Daisy,
Coltsfoot (see pp. 178-80, Figs. 122 and 123), and
Thistle.

(2) Liguliflorae. — Plants with a milky latex and the
florets all strap-shaped, e. g. Dandelion (see p. 181,
Fig. 124), Goat's-beard, and Hawkweed.

Interesting modifications are met with in the florets of the
same capitulum as regards distribution of stamens and
pistils, and the following should be studied :

Usually the ray florets are female and the disk-florets
hermaphrodite as in the Daisy (Bellis perennis) (see p. 178),
Dog Daisy (Chrysanthemum Leucanthemum) , and Corn
Marigold (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
(Petasites 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
(about 150 florets) ; two or three of the outer ones are
male, the rest being female and producing no honey
or pollen. The Groundsel (Senecio vulgaris) 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 ligulate ray-florets and is pollinated by insects.

In a few cases the fruits are dispersed by animals ;
e. g. the Bur Marigold (Bidens tripartita) has hooked fruits
and in the Burdock (Arctium spp.) the bracts end in recurved
hooks and the whole head may be dispersed.

Many Composites are cultivated for their flowers, e. g.
Sunflower, Aster, Dahlia, Chrysanthemum, and Cornflower.

Some are interesting Alpine plants, like the Cudweeds
(Gnaphalium spp.) and the Edelweiss (Leontopodium
alpinum) .

The young flower-heads of the true Artichoke (Cynara
Scolymus) are eaten. The Jerusalem Artichoke (Helianthus
tuberosus) has underground tuberous stems with ' eyes '
like the potato (see p. 130).

The Metachlamydeae or Sympetalae, which contains
more than 42,000 species, shows much greater uniformity
of flower-structure than does the Archichlamydeae.
The parts of the flower are definite in number and cyclic ;
the corolla is usually gamopetalous and the stamens
epipetalous. The ovules 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 which
belong the Lilac, Forget-me-not, Deadnettle, Nightshade,
and Speedwell, the flowers are hypogynous, the parts are
in 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-
bination of characters : the corolla is gamopetalous and
epigynous, and the anthers are syngenesious. The fruit
is 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.

2b4 SYSTEMATIC BOTANY

CHAPTER XXI
CLASS II, MONOCOTYLEDONS

In the second division of Angiosperms, namely Mono-
cotyledons, the embryo has only one cotyledon and is
generally surrounded by endosperm. The plants 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 with
three parts in each whorl. Most Monocotyledons are
perennial 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 semi-
desert 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 with it
in our pastures, meadows, and cornfields ; in grass moors
and cotton-grass mosses ; in reed swamps and the marginal
vegetation 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 include many species well known as
important food plants, and also many garden favourites, e. g.
Gramineae (Grasses, cereals), Liliaceae (Lilies), Amarylli-
daceae (Daffodils), Iridaceae (Irises), Orchidaceae (Orchids).

MONOCOTYLEDONS 265

Order Gramineae. True Grasses, plants usually herbs.
Internodes of stem hollow. Leaves in two rows ; the
base forms a long split sheath, and at the junction
of this with the linear blade is a membraneous ligule.
Flowers in spikelets (p. 201, Fig. 138) enclosed by
bracts or pales. Perianth absent, but sometimes the
two lodicules are regarded as a perianth. Stamens
usually three with slender filaments and versatile
anthers. Pistil of one carpel, and generally two
feathery stigmas. Ovary superior, one-celled, and
contains one ovule.

Floral formula p o, a 3 + o, g1.

This is one of the largest orders of flowering plants and
contains upwards of 300 genera and 3,600 species ; they
occur in all regions of the globe and often form dominant
features in the vegetation, especially in temperate zones.
They are of great economic importance, and are a valuable
source of food for many domestic animals, as the order
contains not only the chief fodder plants, like the meadow
and pasture grasses, but such cereals as Rice, Wheat, Maize,
Oat, Barley, Rye, &c. In tropical countries, and in China,
the Bamboos are used by the natives for innumerable
purposes, e. g. for food, shelter, clothing, furniture, weapons,
and implements.

Order Liliaceae. Plants mostly perennial herbs, hiber-
nating by means of rhizomes or bulbs. Inflorescence
usually a raceme, more rarely a cyme. Flowers
regular, hermaphrodite ; perianth of six free or united
lobes, often petaloid in two whorls of three each.
Stamens usually six, hypogynous. Carpels three,
syncarpous ; ovary superior, three-celled with many
anatropous ovules. Fruit a capsule or berry. Floral
formula p 3 + 3, a 3 + 3, g la) (Fig. 177).

This large order contains many species familiar either as

266

SYSTEMATIC BOTANY

wild plants or cultivated in gardens for their showy flowers,
e. g. the Bluebell (S cilia nutans) (Figs. 87 and 133),
Hyacinths (Hyacinthus spp.), Tulips (Tulipa), Star of
Bethlehem (Ornithogalum umbellatum), Lily of the Valley
(Convallaria majalis), Herb Paris (Paris quadrifolia),
Bog Asphodel (Narthecium ossify agum), Onion and Garlic
(Allium spp.), Solomon's Seal (Polygonatum officinale),

Fritillary, Funkia, and the
Autumn Crocus (Colchicum
autumnale). Some are
climbers, like the beautiful
Gloriosa with leaf-tip ten-
drils, and Lapageria with
twining stems. Some are
very large : e.g. Yuccas,
Dracaenas, Aloes, and the
New Zealand Flax (Phor-
mium tenax). Species of
Asparagus, Smiiax, and
Butcher's Broom (Ruscus
spp.), many of which are
climbers, develop peculiar,
leaf-like stems (phyllo-
clades) (Fig. 96, 2).
Order Amaryllidaceae. Plants similar to Liliaceae but
with ovary inferior. Mostly herbaceous perennials
with bulbs or rhizomes. Inflorescence cymose, and
in bud enclosed in a spathe consisting of two fused
bracts. Flowers regular, sometimes zygomorphic,
hermaphrodite ; perianth of six united petaloid lobes,
in two whorls of three each. Stamens six, epipetalous ;
anthers introrse. Carpels three, syncarpous ; ovary
inferior, three-celled, ovules numerous, placentation
axile. Fruit a capsule or berry (Fig. 134). Floral
formula P3 + 3, A3 + 3, g m.

Fig. 177. Floral Diagram of
Hyacinth. — br, bract.

MONOCOTYLEDONS

267

The order is a large one, and most of the species occur
in dry climates, tropical or sub-tropical. They hibernate
during the unfavourable season by means of their bulbs or
rhizomes. Many are cultivated for their large, showy
flowers : e. g. the Daffodil (Narcissus Pseudo-narcissus)
with a single flower, Jonquil (Narcissus Jonquilla) with
a cymose umbel of flowers, Snowdrop (Galanthus nivalis),
Snowflake (Leucojum),
Agave, Alstroemeria,
Amaryllis, Crinum, and
Eucharis.

Order Iridaceae. Per-
ennial herbs, hiber-
nating by means of
rhizomes, corms or
bulbs. Flowers regu-
lar or zygomorphic ;
perianth petaloid of
six lobes in two whorls
united to form a
tube. Stamens three.
Carpels three, syncar-
pous ; ovary inferior,
three-celled with in-
definite ovules ; style branched, often petaloid ; fruit
a capsule. Floral formula p 3 + 3. A 3 + °. G (3),
(Fig. 178).
Many of the species are adapted to a life in countries
subject 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 135), Iris (Fig. 136),
Ixia, Gladiolus, Freesia, and Tritoma. Very few occur in
Britain ; the most familiar are the Yellow Flag (Iris Pseud-

Fig. 178. Floral Diagram of
Iris. — br, bract.

268

SYSTEMATIC BOTANY

acorus), Foetid Iris or Gladdon (Iris foetidissima) , Crocus
vernus and C. nudiflorus.

Order Orchidaceae, Orchids. Perennial herbs.
Flowers hermaphrodite and irregular. Perianth
usually petaloid, of six lobes, the inner median one
generally forming a lip or labellum. Stamens reduced
to one, rarely two. Carpels three, syncarpous ; ovary
inferior, one-celled ; placentation parietal and bearing

Fig. 179. Floral Diagram of Orchis. — br, bract.

numerous minute ovules. Axis of flower prolonged as
a column above the ovary, bearing the stamens and
stigmas. Fruit a capsule and contains very many
minute seeds. Floral formula P3 + 3, ai + o or

0 + 2, G(3) (Fig. 179).

This order is a very large one, with 400 genera and 6,000
species ; eighteen genera and fifty species occur in Britain,
many of which are rare. They are most abundant in the
tropics, and differ widely in structure according to their
mode of life and habitat ; many occur as epiphytes on the

MONOCOTYLEDONS 269

trunks and branches of trees ; and are dispersed by means
of their very minute and light seeds. Some are saprophytes
(PP- 355-7)» and grow on humus, but most of the species in
temperate regions are terrestrial. They are largely culti-
vated for the brilliant colours and often curious and extra-
ordinary forms of their flowers, which are the most highly
specialized of the Monocotyledons (Fig. 137, p. 199). To
some of them characteristic names have been given.
The more common and interesting British species are :

Early Purple Orchis (Orchis mascula), Spotted Orchis (O. macu-
lata), Butterfly Orchis (Habenaria spp.), Bee Orchis (Ophrys apifera),
Spider Orchids (O. arachnites and aranifera), Fly Orchis (O.muscifera),
Lady's Tresses (Spiranthes spp.), Coral-root (Corallorrhiza innata),
Lady's Slipper (Cypripedium Calceolns), ~fte\\ebox'\r).es>(Epipactis spp.),
Tway Blade (Lister a ovata).

The class Monocotyledons contains about 24,000 species.
The simpler and more primitive forms have no perianth and
the parts of the flowers are spirally arranged and indefinite,
e. g. Pond-weeds (Potamogeton). The flowers of Grasses are
protected by bracts, have few stamens and carpels, and are
pollinated by the wind. The Water Plantain and Flowering
Rush have a double perianth, the parts being in two whorls
of three each. The flowers of the higher forms are cyclic
and have often five trimerous whorls, e. g. Lily and Bluebell.
The most highly developed forms have epigynous and
irregular flowers, with one or two stamens, e. g. Orchids.

PART IV
COMMON TREES AND SHRUBS

CHAPTER XXII
CONE-BEARING TREES

In the vegetation of the earth, trees occupy the first
place. By virtue of their size, 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 yield 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 have
been selected for study.

Scots Pine

Scots Pine (Pinas sylvestris) is commonly planted in
Britain, sometimes forming large plantations, and fre-
quently scattered amongst other trees in woods. It is
sometimes known as the Scotch Fir. In Scotland and
Norway it forms extensive forests. The smaller trunks are

,f;,

• i , 'v..

Fig. 180. A Young Pine, showing branches in false
whorls. — Each ends in a terminal bud surrounded by a few
lateral buds.

Fig. 181. The Narrow-leaved Willow in Winter.

270

CONE-BEARING TREES 271

used for pit -props, and the larger ones as deals. It is an
evergreen tree growing to a height of eighty to one hundred
feet. The bark is thick, rough, and dark below, but a deep
orange above, where the bark peels off in thin flakes.

The branches arise in false whorls (Fig. 180), three or
four at nearly the same level, and spread out horizontally.
The oldest whorl is the lowest, and they are gradually
younger towards the top ; hence the conical form of the
tree. Each branch in turn bears whorls similar to those
of the main axis. The lower, older branches become
broken and die, and often the leader also dies ; then the
upper branches grow considerably and form the broad
crown so common in old pines. The first whorl is formed
in the third year, and one in each following year ; so the
age of the tree may easily be determined.

Examine the end of a branch and note the arrangement
and structure of the buds (see Fig. 67). The parts are
best seen when the buds open, about the middle of May.
The terminal bud is surrounded by three or four side buds
at nearly the same level. Growing on the bud-axis are
many spirally arranged scale-leaves with brown membra-
neous tips. In the axils of all but the lowest two of these
are buds.

Trace the growth of these as the bud opens. Each small
bud becomes a short or dwarf shoot (Fig. 182, 1), bearing
several scales round its base, and at the end arise two
narrow leathery needles. Note their shape and how they
are packed together in the bud. They are semicircular
in section with their flat, upper surfaces applied to each
other. A bud thus gives rise to two kinds of shoots and
two kinds of leaves : (1) long shoots, which bear scale-
leaves only (Fig. 182, 2), and (2) dwarf shoots, which bear
scale-leaves and a pair of green needle-leaves (Fig. 182, 1).
Pine needles remain on the tree three or four years, some
falling each season.

272

COMMON TREES AND SHRUBS

Examine the old fallen needles, and determine the
structures which are thrown off. It is the dwarf shoots
that fall and not merely the needle-leaves.

Examine 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. 182. Scots Pine. — 1, dwarf shoot; 2, elongated shoot
bearing scale-leaves with dwarf shoots in their axils : female cone
near end of branch ; 3, male cone ; 4, a single staminate branch ;
5, pollen-grain ; 6, branch bearing young female cone ; 7, ovule-
bearing scale ; 8, winged Pine-seed ; 9, old female cone ; a, stamens ;
ds, dwarf shoots ; /, foliage-leaf ; m, micropyle ; o, ovule ; po,
pollen-sac ; s.b, staminate branch ; sc, scale-leaves ; w, wing.

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 different branches of the same tree (monoecious).
The male cone (Fig. 182, 3) arises at the end of a branch,
and consists of a central axis which bears a tuft of dwarf
shoots 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 (4). Each
stamen has a very short filament ; and the anther bears
two pollen-sacs on the under surface (po). When ripe,
they split longitudinally and the pollen-grains escape in
immense numbers. Each pollen-grain (5) is provided with
two air-bladders which serve as floats, and it may be
carried a great distance by the wind. When the pollen is
shed, the staminate shoots fall off,
and the dwarf shoots at the tip
develop their pairs 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
it is about a quarter of an inch long,
and appears to be terminal, but later
it is seen to be lateral (2). It remains
on the tree three years, growing
larger each season. The cone con-
sists of a central axis on which are
scale-leaves, and on the upper surface
of each scale-leaf grows a much
larger, thick, flat, woody scale, i. e.

the carpel. On the upper surface of each carpel are two
straight ovules (orthotropous) (7), with their micropyles (m)
pointing towards the axis. They are not enclosed in an
ovary ; there is no style and no stigma ; hence there is
no pistil as in typical flowers.

When ready for pollination the axis elongates, lifting 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. When
ripe the carpels become woody (9), gape open from above
downwards, and allow the seeds to escape, each carrying

Fig. 183. Seedling
Pine. — c, cotyledons ;
/, first green needle-
leaves.

1296

274 COMMON TREES AND SHRUBS

with it a thin shaving from the carpel, which serves as
a wing for seed-dispersal (Fig. 182, 8).

The ovule of the Pine, unlike that of other flowering
plants, becomes filled with endosperm before fertilization.
When ripe, part of this persists around the embryo, which
has a radicle, plumule, and eight needle-shaped cotyledons.
On germination the tips 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 arising in their axils give rise to dwarf
shoots, each with two needle-leaves (Fig. 183).

Larch

Though commonly planted in woods, the Larch (Larix
europaea) is not a native tree in Britain. It grows rapidly
to eighty or one hundred feet, and as in the Pines, the
terminal bud continues growth, and for a time the tree is
conical. The leader is eventually lost, and the tree then
develops an open crown of sparse and delicate foliage. Its
bark is fissured, scaly, and grey, tinged with pink, and is
early developed on the young shoots.

The tree is easily recognized by its knotted, slender,
furrowed branches, which arise alternately and not in
whorls. Long and short shoots are formed ; on the long
ones the leaves arise singly, while on the thick, slow-growing
short shoots they are numerous and in tufts (Fig. 184).
In wet seasons the dwarf shoots may elongate and form
long flexuous drooping twigs. Buds are relatively few and
are scattered on the shoot. Notice the large number of
scale-leaves and foliage-leaves which have no buds in their
axils. The buds stand off at right angles and are covered
with very many brown resinous scales. Most of these fall
off as the bud opens, but the lower ones persist and harden.
The leaves are about an inch long and needle-like, but thin,
flat, and soft. In early spring they are bright green in

CONE-BEARING TREES

275

colour and very conspicuous ; and they transpire freely.
In the autumn they darken, turn brown, and fall off.

The Larch, being the only
European Conifer with deci-
duous leaves, is enabled to
grow in situations fatal to
other Conifers, and it ex-
tends farther northward and
attains a greater height than
any other tree. The small
leaves offer little protection
to the slender shoots, and
dead twigs are common on
the Larch. The ' flowers '
are in cones, similar to those
of the Pine, and both male
and female occur on the
same tree. The male cone
(Fig. 184, 1 m.c), however,
is simpler than in the Pine ;
it consists merely of a cen-
tral axis bearing numerous
stamens and no needle-
leaves. Each stamen (2) has
a green limb at the tip. The
pollen-grains are numerous,
dry, and carried by the
wind. The female cone (1 f.c)
has a tuft of green leaves at
the base ; it is bright red
when young, and the scales
are lax and flexible. The

Fig. 184. Larch. — 1, branch
bearing dwarf shoots with fas-
cicled leaves ; 2, stamen ; 3,
cone-scale bearing on its upper
surface an ovuliferous scale ; 4,
mature female cone ; 5, winged
seed ; c.s, cone-scale ; d.s, dwarf
shoots ; f.c, female cone ; I, limb ;
m.c, male cone ; o, ovule ; o.s,
ovule-bearing scale ; p.s, pollen-
sac.

barren scales (3 c.s) are

longer than in the Pine, and may be seen projecting

beyond the tips of the ovule-bearing scales (o.s), the

s 2

276 COMMON TREES AND SHRUBS

midrib of the latter being prolonged beyond the scale as
a narrow, curved process. The cone (Fig. 184, 4) is mature
in the following spring. It is smaller, more lax, and has
thinner and more flexible scales than the Pine, and the
cones remain on the old twigs many years before breaking
off. The seed is winged (5), and is dispersed by the wind.
For two or three years, the seedling, unlike the parent, is
evergreen.

The Pine 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 deposited
direct on the micropyle of the ovule ; there is no ovary,
style, or stigma ; the embryo-sac of the ovule becomes filled
with endosperm before fertilization ; the egg-cell is en-
closed in a flask-shaped structure known as the arche-
gonium, an organ characteristic of simpler 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
Pine, Larch, and other cone-bearing trees, belong.

CHAPTER XXIII
CATKIN-BEARING TREES

Willow

Two kinds of Willow are very generally recognized :
the ' Palm ' and the Osier. The ' Palm ' or Goat-Willow
(Salix capraea) (Fig. 185) 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 stamens. The leaves, which appear later, are
broad and oval and have somewhat kidney-shaped stipules.

The Osier (S. viminalis) is common in wet hollows, by
stream- and river-sides, and especially in low-lying, marshy
districts, where it is frequently coppiced, i. e. cut close to the
ground. From both adventitious 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 hairy. The leaves (Fig. 78) have narrow
stipules ; the blades are from four to eight inches long,
lanceolate, pointed, and silky beneath.

Another species, the White Willow (S. alba) (Fig. 181),
is common in similar situations, 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. 157),
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 bewildering number
of species, varieties, and hybrids (i. e. crosses between
the different 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. 185,
1 and 2), and the smaller leaf -buds grow into long, leafy
shoots. The end bud, and sometimes more, of the branch

278

COMMON TREES AND SHRUBS

dies (Fig. 78), and growth is then continued by the next bud
below. The flowers (Fig. 185, 3 and 4) have been described
on p. 160, and are in catkins, male and female on separate
trees, i. e. they are dioecious. In the Goat-Willow the cat-
kins appear before the leaves, but in the Osiers leaves and

Fig. 185. The Goat-Willow. — i, leafy shoot bearing female
catkin; 2, branch bearing two male catkins; 3, female flower;
4, male flower ; 5, capsule dehiscing ; 6, pappose seed ; 7, floral
diagram of female flower ; 8, floral diagram of male flower ; a,
stamens ; br, bract ; f.c, female catkin ; n, nectary ; 0, ovary.

catkins are out together. The fruit is a capsule (Fig. 185, 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. 157 is a photograph of fruiting Willows on
a sand-dune ; they have the appearance of being coated
with cotton wool.

CATKIN-BEARING TREES 279

Poplar

Poplars, like most Willows, are trees of damp places, and
they grow best in a deep moist soil. In such situations
several species are commonly planted, e. g. the White
Poplar (Populus alba), the young branches and leaves of
which are covered with white cottony hairs ; the Aspen (P.
tremula), whose orbicular toothed leaves are green and not
cottony ; and the Black Poplar, of which the tall Lombardy
Poplar is a conspicuous and easily-recognized variety.

The Balsam Poplar is often planted, the opening buds
of which are very sticky. The Black Poplar (P. nigra,
Fig. 186) grows quickly and attains a height of ninety to
a hundred feet . Its long, slender, smooth branches curve up-
wards and form a loose, somewhat pyramidal, crown. The
long and pointed buds are covered by four scales, which
are modified stipules like the bud-scales of many trees.

As in Willows, &c. (Fig. 78), the end bud dies, and
growth is continued by the next bud below ; therefore,
branching is sympodial, not, as in the Pine and Larch,
monopodial.

The leaves are uprolled in the bud, and stipulate, but
when the bud opens, the stipules fall off along with the
bud-scales. The leaf-stalk is tough but very flexible,
flattened laterally, and the rhomboid or somewhat triangular
and toothed blade readily quivers in the wind.

This modification, found in some other Poplars as well,
may be useful in two ways : (1) By moving readily with the
wind, the leaves will produce less strain on the branches ;
and (2) the movement of the blade will favour transpiration,
cause an increased upflow of sap, and therefore increased
food-supply, and, in trees growing in a deep moist soil, with
a good water-supply, will favour rapid growth.

In the vicinity of the tree we often find young shoots
springing from the ground and resembling seedling Poplars.

280

COMMON TREES AND SHRUBS

If these are traced they will be found to spring from long
roots of the parent tree which grow horizontally just below
the surface, the main roots being deep in the soil. Such
shoots are called suckers, and they afford a means of vege-
tative propagation. In the late summer or early autumn
the ground near Poplar trees is often strewn with leafy

Fig. 186. Black Poplar. — i, leafy shoot ;
branch-scars ; 3, male catkin ; 4, male flower ;
6, female flower ; b.s, branch-scars ; d, cup-like disk ; s.s, bud-
scale scars.

2, twig with two
5, female catkin ;

shoots, varying in length from one to six feet. These are
deciduous shoots cut off by a separation-layer, as in the
leaves (Fig. 186, 2 b.s). Compare this with what occurs
in the Pine.

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 281

fringed, and in the axil of each is a flower (4), consisting
of a cup-like disk (d), and bearing thirty to forty stamens
with dull 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 (6). The capsules, when ripe, split by two valves ;
and the seeds, each bearing a tuft of hairs at the base, are
dispersed by the wind.

Hazel

The Hazel (Corylus Avellana) (Fig. 187) 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 stools 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. 38), and for
several years forms a smooth shining bark, on which are
prominent transverse lenticels (Fig. 187, 1 /), but, later, the
bark 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 and
covered with bud-scales, the nature of which may be easily
made out by examining an opening bud. Note the transi-
tion from the outer brown scales to scales consisting of pairs
of stipules covered with silky hairs, while the innermost
pairs have each a small blade between them. The stipules
only remain for a short time after the bud opens, but last^
longer on the leaves of the stool-shoots and suckers. The

282

COMMON TREES AND SHRUBS

young shoots are zigzag and hairy, and produce a leaf at
each angle.

The leaves (Fig. 187, 2) are short-stalked ; the blade is
large and somewhat orbicular, with a doubly serrate margin
and a pointed apex, and the surfaces are rough and hairy.
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. 187. Hazel. — 1, flowering branch ; 2, foliage-leaf ; 3, male
flower ; 4, floral diagram of the male cyme ; 5, two female flowers
in axil of bract ; 6, floral diagram of female cyme ; 7, fruiting
branch; 8, fruit in longitudinal section; a, anthers of branched
stamens ; br, bracts ; c, cotyledon ; cu, cupule ; f.c, female catkin ;
I, lenticel; m.c, male catkin; p, plumule; pe, perianth; r, radicle;
st, stigma.

into a long, zigzag shoot ; but those below form dwarf
shoots, some of which produce a tuft of leaves, while others
become flower-buds. Those which will form male catkins
do not rest during the winter, but elongate the same year ;
hence we find tightly-packed male catkins hanging on the
trees in winter (Fig. 187, 1). In mild weather they may
open in December, but in severe weather they may remain
closed until the end of February or the beginning of March.
The Hazel is monoecious. The male catkins (Fig. 187, 1

CATKIN-BEARING TREES 283

m.c) are pendulous, and one and a half to two inches long
when open. Each bears a number of bracts, and within
each bract are two smaller bracts (3 and 4 br.). The flower
consists of four halved or split stamens. The filament is
divided into two, and each bears at its end half an anther.
Thus the flower appears to have eight stamens.

The female catkin (i/.c) resembles a leaf-bud, but is
rather larger, and, when mature, bright red stigmas
project from it. Its outer structure is like a leaf-bud, and
consists of a covering of brown scales followed by stipules
and small leaves. In the centre are four or five bracts,
each with two flowers in their axils (5). The ovary is
inferior and bears a minute perianth (pe) ; on the top are
two long red stigmas. At the base is a cupule composed of
three scales (cu).

After fertilization, the wall of the ovary hardens into
a woody shell, the perianth and stigmas shrivel up, and the
three scales at the base enlarge and form a leafy cupule
enclosing the nut (7 and 8). The seed is attached by a long
stalk, has a thin brown testa, a small radicle and plumule,
and two large cotyledons stored with oil (8 c).

Birch

The Birch (Fig. 188) is characteristic of dry upland woods
and heaths, and occurs frequently in the wet fen woods. It
is at once recognized by its white, papery bark, and slender
switch-like branches. It is a small graceful tree, the trunk
being from eight inches to a foot in diameter and attaining
a height of forty to fifty feet. The base is covered with a
rugged black bark ; above, it is white and shining, and peels
off in thin flakes ; it is marked transversely by long dark
brown lenticels. The younger branches are brown at first,
changing later to white.

Two species (and several varieties) occur, and are most
readily distinguished by their young shoots. The common

284 COMMON TREES AND SHRUBS

Birch (Betula tomentosa) is the most abundant. Its branches
are greyish-brown, slender, but seldom droop, and the
fresh young twigs are hairy. The Silver Birch [Betula
alba) is a more elegant tree 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, and
the 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 it 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, its small scattered leaves (Fig. 188, 2)
do not form mosaics, and neither shade each other nor cast
much shade on the ground. It grows badly under the
shadow of other trees, 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 on
the same tree (monoecious). The male catkins are deve-
loped in the autumn, and are seen on the trees throughout
the winter, two or three together at the ends of the twigs
(Fig. 188, 1 m.c). 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 4). On the upper side of each bract are two
smaller bracts (3 br) ; then three flowers, each with two
split 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 (4). Each bract has two small scales above it

Fig. 188. Birch. — i, winter shoot; 2, leafy shoot; 3, floral
diagram of male cyme ; 4, floral diagram of female cyme ; 5, bracts
of female flower ; 6, winged nutlet ; br, bracts ; d.s, dwarf shoot
with foliagedeaves and fruiting catkins ; f.c, female catkins ;
m.c, male catkins ; t, dead terminal branch.

286 COMMON TREES AND SHRUBS

(Fig. 188, 5) and three small flowers. Each flower consists 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 nutlet
(6). The catkin elongates as it ripens (2 f.c), and the
bracts with the two scales attached, as well as the winged
fruits, are scattered by the wind.

Alder

The Alder (A Inns glutinosa) (Fig. 189) is a characteristic
tree by stream-sides and in low-lying marshy districts,
where, along with Willows, it often forms a characteristic
thicket. It is usually a small tree, rarely more than fifty
feet high, and, growing from the base of the trunk, are
often many stool-shoots, which give it 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, it is a light-demanding tree, 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 Alder
thicket is often a rich purple. The longer quick-growing
shoots are smooth, but with conspicuous reddish lenticels,
and somewhat triangular in section on account of the
prominent decurrent leaf-bases (Fig. 189, 1 and 2 Lb).

The buds are rather large, triangular, and distinctly
stalked (b) by a slight elongation of the axis beneath the
lowest 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. 189, 3), coated with a waxy secretion, and are not easy
to separate. Note the relationship between leaves and

CATKIN-BEARING TREES

287

Fig. 189. Alder. — i, autumn shoot ; 2, flowering shoot ; 3, section
of leaf -bud ; 4, male cyme ; 5, diagram of male cyme ; 6, female
cyme ; 7, diagram of female cyme ; b, stalked buds ; br, bracts ;
c, 'cone' with fruits; d, dead 'cones'; d.b, dormant buds; f.c,
female catkins ; I, leaf ; I. b, decurrent leaf -bases ; le , lenticels ;
m.c, male catkins ; s, stipules ; sc, scale-leaves ; 5/, stigmas.

288 COMMON TREES AND SHRUBS

stipules as shown in the diagram. On the lower part of the
shoot 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 has 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
occur on the same tree. Both are developed in the summer
and may be seen on the tree before the leaves fall (Fig. 189, 1).
They are thus exposed throughout the winter and open
about February in the following year, before the leaves
appear (2). The male catkins (1 and 2 m.c) are long and
pendulous. On the upper surface of each bract, and united
to it, are four scales (5 sc), 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 and 7).

When fertilized the ovary becomes a dry, flattened, one-
seeded nutlet. Each bract with its four scales grows and
becomes a green five-lobed woody scale, the whole resem-
bling a small Pine cone (1 c). The nutlets ripen in the
autumn but are retained until the following spring ;
the 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 remain
several years on the trees before they are broken off (1 d).

Note the different years' flowering shoots represented
on the branch in Fig. 189, 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 still are
the old cones (d), which shed their fruits the previous year.

Fig. 190. Beech Wood in Winter.

288

CATKIN-BEARING TREES 289

Beech

The Beech (Fagns sylvatica) (Fig. 190) is one of the
largest of British trees and occurs most extensively in the
chalk districts of the south of England. In the north it
is commonly planted, but doubtfully native. It attains
a height of one hundred to one hundred and twenty feet ;
and in woods it develops a tall, straight trunk, extending
to the crown and having few branches below. In the open
it forms large branches low down on the trunk, and in
consequence its wide-spreading crown comes nearly to the
ground. From its base several massive buttresses are given
off, which extend into the shallow main roots. Its bark is
thin, very smooth and olive grey, and on the exposed side
of the trunk numerous shoots may develop, which serve
to protect it.

Two kinds of branches are formed, and give a character-
istic aspect to the tree : (1) the quick-growing, slender,
zigzag shoots with a bud standing off at each bend (Figs. 74
and 191), and (2) the slow-growing dwarf shoots, the ages
of which may be determined by counting the sets of scale-
scars on them (see p. 115).

The end bud of the long shoot sometimes dies, then
growth is continued by the next bud below, which gives
rise to a long shoot. The lower, lateral buds are displaced
to the upper side of the leaf-scar and form dwarf shoots.
Each produces three or four crowded leaves, which vary in
size. By the bending of the leaf-bases all the blades are
brought into a horizontal plane and form an excellent
mosaic (Fig. 191, 1).

The lowest leaves of a shoot produce only small buds
in their axils, and these remain dormant ; no buds are
formed in the axils of the leaves of dwarf shoots, growth
being continued by the end bud. The buds are long, thin,
oval, and pointed, and covered by about twenty light-brown

1296 T

2go

COMMON TREES AND SHRUBS

membraneous scales, which are stipules. The leaves are
folded fan-wise and covered with silky hairs (Figs. 72, 75, 76).
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. 191. Beech. — 1, leafy shoot showing leaf -mosaic ; 2,
flowering shoot ; 3, male flower ; 4, female flower ; 5, fruit enclosed
in a spiny cupule ; a, stamens ; by, 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 silky beneath ; the margin is wavy and,
when young, fringed with hairs.

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 291

Beech, forming tiers of mosaics facing the sky, produce
a closer canopy and cast a deeper shade than any other
British tree, and the vegetation beneath is very scanty.
As regards light, it stands at the opposite extreme to the
Birch : 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. 191, 2). The male flowers are in
a globular cluster at the end of a long, pendulous stalk.
Each flower has a perianth of four to seven hairy lobes
(3), 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 single flower consists of a three-celled
ovary with two ovules in each cell, and three red stigmas.
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 (5), and
when ripe splits into four valves. One nut is formed in
each flower; it is triangular, with a smooth brown coat,
and contains only one seed.

Oak

The Oak (Fig. 192) is the largest and most characteristic
of British trees, and formerly Oak forests covered a large
part of England. Two species are common, and they
sometimes characterize distinct habitats. The Sessile Oak
(Quercus sessiliflora) is the dominant tree on shallow, poor
siliceous soils, and is typical of the woods on the Pennine
slopes, and other similar hilly regions. The Peduncled
or Stalked Oak (Q. Robur) is often the prevailing tree in
lowland woods, with a deep rich siliceous soil over clays
and loams. On soils containing much lime, both species
tend to occupy a very subordinate place in the vegetation.

t 2

292 COMMON TREES AND SHRUBS

Often the two species grow together, then hybrids between
them are frequent. The Oak grows to a great age and size,
and weather-beaten specimens, like the Cowthorpe Oak in
Yorkshire, may have a trunk seventy feet in girth. The
trunk 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 end
in clustered twigs. The bark is rugged, with deep vertical
furrows ; the ridges break transversely and form oblong
scales (Fig. 193).

The buds are crowded around the ends of the twigs
(Fig. 194). If the end bud persists, it 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 are
small and remain dormant (Fig. 194, 1 d.b). The buds are
stout, 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. 194, 2), and the small brown
stipules soon fall off. The base is curved, swollen, and
continued as two lines down the stem, and on either side of
it is a stipule-scar. In August and September the separa-
tion-layer is seen distinctly across the leaf-base. The leaf-
stalk is grooved above and longer in the Sessile than in the
Stalked Oak ; the blade is obovate, deeply and irregularly
lobed (sinuate), and somewhat leathery. In the Sessile Oak,
the base of the blade is more or less tapering, and has many
branched hairs on the under surface. In the Stalked 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.

Fig. 192. Oak in Winter.

292

Fig. 193. Oak Bark.

CATKIN-BEARING TREES

on-2

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. 194, 3) arise either in the axils of the

cu.

Fig. 194. Oak. — 1, winter twig ; 2, leafy shoot ; 3, male catkins >
4, male flower ; 5, female flower ; 6, vertical section of female
flower ; 7, diagram of female flower ; cu, cupule ; d.b, dormant
buds ; sc, scale-scars.

lower leaves or lower on the shoot from buds of the previous
year. 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

294 COMMON TREES AND SHRUBS

stamens (Fig. 194, 4). 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 Stalked 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 (7), with two ovules in each cell,
but the ovules are not formed until after pollination. The
stigmas 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. 143.

A comparison of the flowers of such catkin-bearing trees
as Hazel, Birch, Alder, Beech, and Oak shows that they
differ in several important respects from those of Willows
and Poplars. In the Willows and Poplars (Salicaceae) the
flowers 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 fruit is
a dehiscent capsule, and the seeds have a tuft of hairs.
In the Hazel, Birch, and others, the flowers are monoecious,
and have an epigynous perianth. The pistil has two or
three united carpels ; the ovary is two-celled with one or
two ovules in each cell, and the fruit is an indehiscent, one-
seeded nut.

In each case the flowers are small and inconspicuous.
The stamens produce a large quantity of dry pollen carried
by the wind to the large branched stigmas of the female
flowers.

TREES WITH HIGHLY-DEVELOPED FLOWERS 295

CHAPTER XXIV

TREES WITH MORE HIGHLY DEVELOPED

FLOWERS

The flowers of some of our forest trees and shrubs are
so conspicuous, that they have earned the popular name
of ' flowering trees ' and ' flowering shrubs '. They differ
from the previous types in usually having both stamens
and pistils in the same flower (i.e. they are hermaphrodite),
and often have a well-developed perianth. The less con-
spicuous of these are the Elm, Sycamore, and Common
Ash ; on the other hand, the Rowan, Laburnum, Horse-
Chestnut, and Lilac, have very showy flowers, attractive to
insects, which pollinate them.

Elm

The Wych Elm (Ulmus montana), also known as the
Scots or Mountain Elm, is a native of Britain and is northern
and upland in its distribution, in which districts it com-
monly occurs in the damp woods and hedgerows. Another
species, the English Elm {Ulmus campestris), is not native,
and occurs most commonly in the lowlands and southern
half of England (Fig. 195, 1 and 2). There are also many
varieties.

The Elms are tall trees, eighty to one hundred and twenty
feet high, with a deep and coarsely-fissured bark (Fig. 195, 1),
resembling that of the Oak. The crown is large and spread-
ing, and the lower part of the trunk is often thickly clothed
with stool-shoots.

The buds and twigs are more hairy, and the latter thicker,
in the Wych Elm than in the English Elm. The terminal

296 COMMON TREES AND SHRUBS

bud often dies, and growth is continued by the next lower
bud (Fig. 77). This grows into a long shoot, while the
lower lateral buds form dwarf shoots as in the Beech, with
a similar type of leaf -mosaic (Fig. 197). In flowering

Fig. 197. Leaf-Mosaic of Elm.

branches the small, pointed, upper buds produce leafy shoots,
but below these are larger globular buds which produce
clusters of flowers (Fig. 198, 1).

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. 198. Elm. — 1, flowering branch ; 2, opening leaf-buds ;
3, Elm flower ; 4, winged fruit ; s, stipules.

298 COMMON TREES AND SHRUBS

smaller, ovate to cordate, and nearly smooth above. The
stipules (Fig. 198, 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 position
of dwarf shoots, each containing a cluster of sixteen to
eighteen 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. 198, 3). The perianth is inferior
and 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 thin,
flat, veined wing surrounding the single seed. The end is
often deeply notched and the two edges overlap (Fig. 198, 4).

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 their seeds.

Rowan

The Rowan (Pyrus Aucuparia), as is usual with well-
known 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

TREES WITH HIGHLY-DEVELOPED FLOWERS 299

the trunk is covered with a thick, furrowed bark, while it is
thin and smooth above. Suckers are readily formed from
the roots, and the branches are ar-
ranged spirally and come off from
the tree at an acute angle.

The twigs are stout and covered
with a smooth, shining, grey to deep
red-brown bark ; the lenticels are
few but distinct, transverse, and
yellowish. The dwarf shoots (Fig.
199, d.s) are stout, prominent, and
densely ringed ; and their ruggedness
is intensified by the rather promi-
nent crescent-shaped leaf-bases, each
with five leaf-traces. The cortex,
when bruised, and also the flowers,
have an unpleasant smell of decaying
fish.

The terminal buds are ovoid, large,
and shining, and covered with five
or six velvety and fringed bud-scales ;
the lateral buds are smaller and
pressed against the stem ; the end
buds of the dwarf shoots elongate
very little and produce each season
from three to five leaves crowded
together.

The leaves are alternate and
stalked, and have prominent leaf-
bases and deciduous stipules. The
blade is pinnate and divided into
eleven or more sessile, oblong leaflets,
always with an odd terminal stalked leaflet. The leaflets
are one to two inches long, serrate, smooth above, and
slightly hairy below, and have pinnate veins.

Fig. 199. Winter
Shoot of Rowan. —
d.s, dwarf shoots with
numerous scale-scars ;
l.s, foliage leaf-scars.

3oo

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 small
flowers. The flowers (Fig. 200) open in May or June
The receptacle forms a deep cup with the five sepals, five
petals, and about twenty stamens attached to the rim. The
pistil consists of two or three united carpels which are in
turn united to the receptacle-cup (2). The styles are

Fig. 200. Rowan. — 1, 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 stigmas
are ripe 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 (1). Round the base of the styles is a honey-
secreting ring, and the honey is partly protected by hairs
projecting from the styles.

Numerous insects visit the flowers, such as beetles, flies,
and bees, but, if their visits are ineffective, self-pollination
takes place. After fertilization the receptacle becomes

TREES WITH HIGHLY-DEVELOPED FLOWERS 301

fleshy ; the carpels form the core enclosing 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 (Ancuparia) is derived from the fact that
its berries were used to entice redwings and fieldfares into
nooses of hair suspended in the woods.

Laburnum

The Laburnum (Cytisus Laburnum) (Fig. 201), so often
grown as an ornamental tree, is not a native of Britain, but
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 is
a small tree, fifteen to twenty feet in height, with lax, often
drooping, branches. The bark remains smooth for many
years, then becomes fissured longitudinally ; the branches
are greenish-brown to olive, and the young shoots are grey-
green and covered with silky hairs.

The end buds are white, silky, and surrounded by several
prominent leaf-bases (1), on which are narrow persistent
stipules, giving the buds a fringed appearance. The
lateral buds are rather smaller and flattened, and rest
on prominent leaf-bases. Many of these buds are sup-
pressed or dormant, especially on the concave side of the
branch ; 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 rather
loose scales which show transitions to foliage-leaves, thus
proving that they are reduced leaf-bases (2). The leaves
on the long shoots are alternate and separated by

302 COMMON TREES AND SHRUBS

Fig. 20 i. 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-stalk twisted ; 6, flower in front view ;
7, vertical section of flower ; 8, floral diagram ; a, alae ; d.s, dwarf
shoots ; /;, honey-guides ; k, keel : l.b, latejal bud ; st, standard ;
s.t, stamen-trough.

TREES WITH HIGHLY-DEVELOPED FLOWERS 303

distinct internodes, while those on the dwarf shoots arise in
tufts (Fig. 201, 3). The leaves are alternate and compound ;
the base is small with narrow persistent stipules ; the
petioles are long, and the blade is trifoliate. Each
leaflet is attached by a short stalk, and is entire, ovate,
and pointed ; the upper surface is smooth ; the under
surface silky white, especially when young.

The inflorescence is a lax drooping raceme (4). The
flowers are irregular, pea-like (papilionaceous), and open
in May. The calyx is two-lipped and consists of five
united but unequal sepals. The corolla has five petals, as
in the Sweet-Pea. The drooping habit of the raceme
inverts the flowers. This, however, is righted by the
twisting of the young flower-stalk (5), and thus the
standard is brought into its usual conspicuous and erect
position (6). The honey is quite concealed and secreted
in a swelling at the base of the standard, which has two
dark honey-guides directed towards the nectary. The
receptacle is slightly hollowed, and the petals and also the
stamens are joined to the side of it, being therefore peri-
gynous (7). The ten stamens are all joined (monadelphous)
(8), and are ripe before the stigma. The pistil has only
one carpel ; and the style, together with the stamens, is
upturned in the keel.

The flowers are visited by bees, and after each visit the
keel springs back into its place ready to be revisited. The
fruit is a pod, constricted between the seeds and covered
with dark brown hairs. The seeds and other parts of the
tree are poisonous.

Sycamore

The Sycamore (Acer Pseudo-platanus) (Fig. 202) is a
native of Middle Europe, but not of Britain. It is, however,
a very familiar tree in woods, parks, and hedgerows. Often,
when the Oak is cut down in the woods, the Sycamore is

304 COMMON TREES AND SHRUBS

planted in its place and so becomes a common woodland
tree. It also tends to spread by self-sown seedlings. In
Scotland it is known as the Plane Tree, but it must not be
confused with the true Plane so commonly planted in
London, which is a form of Platanus acerifolia.

It is a large tree, fifty to sixty feet high, with a wide-
spreading, somewhat pyramidal, crown. The ash-coloured
bark is smooth, and in the old tree scaly, but not fissured.
The terminal bud continues growth ; therefore branching
is monopodial. The buds are in crossed pairs (Fig. 70), the
terminal and also the flowering buds being larger than the
lateral buds. The branches are slaty-grey to reddish-brown,
and are dotted with numerous lenticels. The details of
a shoot, the structure of a bud, and the formation of the
leaf-mosaic have already been described (pp. 113-14, Figs.
70, 71, and 73).

Beneath a Sycamore on the side of a road the pavement
is 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 if 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 time give rise to a forked branch
(false dichotomy).

The flowers arise in large end buds. The inflorescence
(Fig. 202, 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 of
a cyme (2) is complete, and consists of five sepals and
five petals all similar, greenish-yellow, and free. There

Fig. 202. Sycamore. — 1, flowering branch ; 2, hermaphrodite
flower ; 3, male flower ; 4, pistil ; 5, double samara ; 6, vertical
section of seed showing the folded cotyledons ; a, anther ; c,
cotyledon ; d, disk ; /, funicle ; p, plumule ; r, radicle ; sc, scale-
scars ; st, stigmas ; t, testa.

use

306 COMMON TREES AND SHRUBS

are eight stamens together with a pistil 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 often
staminate, and the pistil, when present, is small and abortive
(Fig. 202, 3). 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 visit the flowers.

The fruit or ' key ' (see p. 214) is a double samara
(5), and 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 Hippocastanum) (Figs. 66,
68, 69, and 103) is a native of Greece and Asia, where its
seeds are ground and mixed as a medicine with horses' food ;
hence its 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 from
the edible Chestnut (Castanea). It is commonly planted
in Britain as an ornamental tree. 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
in the young trees very regular, with a tendency for the
inner branches to be smaller. The branches curve down-
wards and outwards, and in open situations the end twigs
are markedly upturned and end in very large, sticky, red-
brown buds, the structure of which has already been
studied (pp. 108-13).

TREES WITH HIGHLY-DEVELOPED FLOWERS 307

As is commonly the case with buds, the last leaves formed
in the season are greatly reduced and become the oldest and
lowest scales of the winter bud, and sometimes traces of
blades are found on their tips. Note the number and the
different lengths of the internodes in a year's growth, and
compare the shoot with one-year shoots of other trees.
Often the lowest nodes are short, then follow longer ones,
and finally shorter ones again at the end of the season. The
leaves appear early, and this often leads to irregular growth.
For if the leaves are killed by late frosts, as is frequently the

Fig. 203. Flowers of Horse-Chestnut. — r, male flower ;
2, hermaphrodite flower : female stage ; 3, later stage : stamens
raised to level of stigma.

case, new leaves are produced from buds which otherwise
would not have opened until the following season.

The flowering buds are very large (Fig. 103) ; the inflo-
rescence is a big erect panicle ; the main axis is racemose
and the branches are cymose. After flowering, the inflo-
rescence is cut off by a cork layer forming a large scar, which
has a bud on both sides (Fig. 68, 5) ; with the growth of
these, false dichotomy results. Three kinds of flowers
often occur in the same inflorescence through abortion :

(1) upper male flowers, which open first (Fig. 203, 1) ;

(2) perfect (hermaphrodite) flowers, in which the stigma
ripens before the stamens (Fig. 203, 2) ; (3) abortive
flower-buds, which fall off without opening.

The flower is irregular, has five sepals, five petals (though

u 2

308 COMMON TREES AND SHRUBS

sometimes there are only four), seven stamens, and a superior
pistil of three united carpels. The ovary is three-celled,
with two ovules in each, and above is a single long style.
At the bases of the young petals are yellow spots which
later turn red. The anthers and pollen are also red.

The flowers are visited by bees and are well adapted to
the size and habits of the humble-bee. The upper flowers
with an abortive ovary, open first (Fig. 203, 1). Later,
the perfect flowers open, the style projecting horizontally,
and the stigma is ripe before the stamens, which, at this
stage, hang downwards out of the way (2). 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 style, and shed their pollen, and
so may effect self-pollination (3). The bee presses its
legs between the petals, and pushes its proboscis into the
flower to obtain honey from the disk on the outside of the
stamens. In doing so, the hinder part of its body touches
the stigma and also the ripe anthers, and at the same time
it carries away pollen on the bases of its middle and hind
legs. The fruit is formed from the ovary and becomes a
large and spiny capsule. When ripe it splits into three
valves, each containing two large brown seeds.

Common Ash

The Common Ash (Fraxinus excelsior) (Fig. 204) is a
native tree, widely distributed in Britain in very different
habitats. It is especially characteristic of the woods of
the rocky and scree-covered limestone hills in the north
and west of England, in which it is usually the dominant
tree. In non-calcareous areas it is common in the wet
soils along stream-sides and is frequent in the wet carr
woods of lowland and fen districts." It is sometimes cop-
piced. The tree attains a height of eighty to a hundred

TREES WITH HIGHLY-DEVELOPED FLOWERS 309

feet, and the trunk extends almost to the top of the oval
pyramidal, but loose, crown. The bark (Fig. 196) has the
form of a meshwork of oval longitudinal fissures. Shoots
often spring from dormant buds on the trunk. The branches
arise in crossed pairs and are greenish-grey to olive-green.

Fig. 204. Common Ash. — 1, winter twig; 2, leafy shoot; 3,
flowering shoot ; 4, male flower ; 5, hermaphrodite flower ; 6,
young fruiting branch ; 7, floral diagram of hermaphrodite flower ;
db, dormant buds ; l.s, leaf-scar ; sc, scale-scar.

They remain smooth for a long time ; then become finely
fissured and have a few scattered, longitudinal lenticels.
The twigs (Fig. 204, 1) are thick, smooth, often upturned
at the ends, and sometimes form false whorls. Dwarf
shoots are common and very knotted. The terminal buds,

310 COMMON TREES AND SHRUBS

which are the largest, are short, and covered with velvety
black hairs. Though sometimes separated by a short
internode, the lateral buds are generally opposite and in
crossed 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 pairs, but
sometimes they are alternate (Fig. 204, 2). The base is
large and has no stipules ; the petiole and midrib 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 irregularly
serrate ; the apex is long and pointed (acuminate). In
young trees, during damp weather, drops of water exude
from water-pores at the leaf-tips. When the leaves fall,
a separation-layer forms across the bases of the leaflets as
well as across the leaf-base. This occurs also in the Horse-
Chestnut.

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 Pines, the young main
shoot grows rapidly towards the light and so forms a tall,
slender trunk ; hence Pines, in such circumstances, are
called ' Nurses ' by foresters.

The flowers appear in April or May and before the leaves.
The inflorescences (Fig. 204, 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

TREES WITH HIGHLY-DEVELOPED FLOWERS 311

merely of two stamens joined at the base (4). The
female flowers have a much-reduced calyx and a superior
pistil of two united carpels, and there are two large stigmas.
The hermaphrodite flowers have no perianth, but two
stamens below the pistil (5).

The flowers are wind-pollinated, and only one seed
matures. As the fruit ripens, the free end of the ovary
enlarges into a flat, leathery wing, and forms a samara
carried by the wind. A young fruiting branch is shown in
6, and the floral diagram in 7. The structure of the fruit
has already been studied (p. 24, Fig. 9, 1 and 2).

Lilac

The Lilac (Syringa vulgaris) (Fig. 205) is a native of the
wooded slopes of Persia and Central Europe, and was
introduced into Britain at the beginning of the seventeenth
century, when many of our common ornamental trees were
brought to this country. It is a shrub ten to fifteen feet
high, and is often surrounded by numerous suckers from the
roots. The suckers grow rapidly, forming long, straight,
switch-like shoots. This increase in vegetative growth
tends to reduce its flowering activity, hence the removal
of the suckers in cultivation.

The bark is greenish-brown, fissured and scaly ; and the
small, slender branches are grey to olive, with conspicuous
oval lenticels.

The end bud of the ordinary branches often dies, and
since the lateral buds are in crossed pairs, this leads to
the forked branching (false dichotomy) which is such a
striking feature of the shrub. The large inflorescence-bud
is also terminal, and forked branching occurs here after
flowering, as in the Sycamore and Horse-Chestnut.

312

COMMON TREES AND SHRUBS

Many variations in bud-suppression will be found by
careful examination of a Lilac shrub (Fig. 205, 1 to 5) :

(1) The lowest two or three pairs of buds on a shoot are
very small, and usually remain dormant (db) ; (2) the

Fig. 205. Lilac. — 1, winter shoot : terminal buds suppressed,
lateral buds vigorous ; 2, forked branch formed from lateral buds,
between which are the remains of an inflorescence ; 3, branch with
persistent terminal buds, the two lateral buds dormant ; 4, terminal
flower-bud ; 5, dwarf shoot ; 6, young leafy shoot, showing transi-
tion from scaledeaves to foliagedeaves ; 7, flower ; 8, vertical
section of flower ; 9, inflorescence of Privet ; 10, part of inflorescence
showing flowers in small cymes ; a, anther ; db, dormant bud ;
ds, dwarf shoot ; f.b, flower-bud ; i, remains of inflorescence ;
ov, ovary; s, bud-scales; sc, scale-scars; st, stigma; s.t, suppressed
terminal bud.

terminal bud often dies and growth is continued by the
next pair below (1 s.t) ; (3) the terminal bud may persist,
and suppression occur in one or both of the next buds
below (3 db) ; (4) often one of a pair lower down is
dormant (5 db) ; (5) occasionally buds grow very slowly
and form dwarf shoots (2 and 5 db).

TREES WITH HIGHLY-DEVELOPED FLOWERS 313

A comparison should be made of shrubs showing different
degrees of bud-suppression, and it 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 prominent
leaf-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 foliage-leaves
within 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 representing several fused veins. The leaf-cushion is
prominent and is continued as two ridges through the
length of the internode, the position of the ridges changing
with each node. The leaves have no stipules ; the stalk
is long, and the blade cordate to ovate ; the margin is
entire, ending in a long point (acuminate), and the surface
is smooth (Fig. 205, 6).

The inflorescence is a large, erect, loose panicle of small,
but showy, flowers, similar to those of the Privet (Fig. 205,
9 and 10). The small calyx has four united sepals ; the
four lilac to purple petals are united into a long narrow
tube with four limbs spreading crosswise, and on the
corolla-tube are two short-stalked stamens (7 and 8).
The pistil is superior and consists of two united carpels,
and the style is divided above into two stigmas which
stand just below the anthers. The last named nearly
fill the entrance to the tube and protect the honey,
which is secreted by the ovary and rises somewhat in
the tube.

Honey, scent, and colour attract numerous insects, the
long tube favouring the long-tongued species. If their
visits are not effective, pollen may fall on to the stigma,
and bring about self-pollination.

314 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 Privet flower
(Fig. 205, 10) is very similar to the Lilac, and they should
be compared.

Fig. 206. Vegetation of Lake, Wood, Moor, and Mountain.

34*

Fig. 207. Mustard Seedlings in Different Kinds of Soil.—
1, surface soil ; 2, sand ; 3, clayey subsoil ; 4, clay.

3'S

PART V
ECOLOGY

CHAPTER XXV
PLANT HABITATS AND COMMUNITIES

Vegetation of the valley and mountain. — In a walk from
the bottom of a valley to the top of a mountain many
striking changes in the vegetation are met with (Fig. 206).
Below is the river, with, perhaps, here and there, ponds or
lakes bordered with reeds, rushes, and other moisture-
loving plants, and trees such as Alders and Willows. The
flat ground beyond, composed of alluvium laid down in
the past by the river, is highly cultivated and occupied
by cornfields and meadows, bounded by hedgerows, with
occasional undrained patches of marsh. On the rising
ground these meadows gradually give place to pasture 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 still, the trees dis-
appear and give place to wild, bleak moorland, perhaps
covered with deep, wet, acid peat (Fig. 209) ; while the
rocky peaks forming the summits are covered with a vege-
tation 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

<--.

CJ "5

—

<o~

C/)

«!

^ _

o «^

1— 1

hi "*"

til

w
<

D
O

In
O

Z
O

K> tO ^■«0W'-,O(yv00(^V0<0 ^

PLANT HABITATS AND COMMUNITIES 317

also to a rarefied atmosphere. These changes of altitude,
slope, climate, aspect, soils, and water-supply sort out,
as it were, groups of plants, each with its own character-
istics, and so completely is this done that it imprints
itself on the landscape.

The diagram, Fig. 208, is a transect extending from the
summit of a hill to the valley below, and shows the striking
changes in the types of vegetation. The high ground is
treeless. To the west is a wet, peat-covered Cotton-grass
moor (A). Rising above is a rocky summit with stony
slopes, dominated by Bilberry (Vaccinium Myrtilkis) (B),
and along with it are Ling (Calluna vulgaris) and rolled-
leaved Grasses. These moorland species extend down the
slope, but here the most conspicuous species is the Bracken
(C). The zone of Oat cultivation (D) now begins, but the
area is largely given up to pasture. In the higher part of
this zone the Oak reaches its upward limit. At the lower
level is the zone of Wheat cultivation (E), but, as in the
Oat zone, pasture-land predominates.

Factors affecting the distribution of vegetation. — In
Britain the factor which has the greatest influence
on plants is the soil, and some of its constituents are
much more effective in determining the distribution of
plants than others, e. g. water-content, humus, acidity,
and lime, which are therefore called determining factors.
A given habitat will, with the varying seasons, be subject
to a more or less definite cycle of climatic conditions, e. g.
temperature, rainfall, atmospheric humidity, and wind.

The conditions affecting plant growth due to topography,
e. g. large mountain masses, altitude, exposure, and slope,
are known as topographic or physiographic factors ; those
due to soil-conditions are edaphic factors ; temperature,
precipitation (i. e. rainfall and humidity), and winds are
climatic factors.

The vegetation of a given area will thus be under the

318 ECOLOGY

influence of a series of factors, topography, soil, and climate,
which will permit or favour the growth of certain species
to the exclusion of 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 such
habitats. 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 grow
in water are known as aquatic plants or hydrophytes
(Gr. hydor = water, phyte = plant). Plants growing in
marshy ground, as on the sides of ponds, ditches, and
rivers, or in wet hollows in woods, are called hygrophytes
(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. 210), moors, and deserts. Such plants are
called xerophytes (Gr. xeros = dry), while plants growing
in a salt-marsh are known as halophytes (Gr. hals = salt).
Every gradation, however, is found between hydrophytes
and xerophytes, and it is impossible to draw a sharp line
between them, but it has been found convenient to speak
of plants adapted to habitats intermediate between the
two extremes as mesophytes (Gr. mesos = intermediate).
Included under the name mesophytes are plants very
varied in habit, form, and structure. Those which show
marked seasonal differences, e. g. plants with deciduous
leaves, which are mesophytes in summer and xerophytes
in winter, are called tropophytes (Gr. tropos = change).

«
o
o

If)
in

9
o

H
H
O

o
g

■9)

o
6

318

■

PLANT HABITATS AND COMMUNITIES 319

Plant-communities. — The whole of the vegetation of
a habitat composed of plant-communities which are deter-
mined by the generally constant soil and climatic conditions
in that habitat is called a plant-formation. The vegeta-
tion of sand-dunes, also that of salt-marshes (Fig. 211),
furnishes good examples of plant-formations ; other exam-
ples are aquatic, marsh, fen, and moor formations. There
are also extensive and complex formations like those on
siliceous soils and those on calcareous soils.

Minor variations of the habitat within the formation
give rise to well-marked plant-communities, such as the
Heather moor, the Cotton-grass moor, the Grass heath,
the Sessile Oak wood, the Pine wood, and the Limestone
Ash wood, which are easily recognizable during a country
walk as characteristic features in the landscape.

These plant-communities within a plant-formation are
called pi ant- associations, and are usually dominated by
one or a few species of plants, often with a characteristic
form and habit, e. g. the small, rolled-leaved evergreen
shrubs of the Heather moor, the tussocks of Cotton-grass
on the Cotton-grass moor, or the dominance of true grasses
on the Grass heath ; and, in the case of woodlands, the
prevailing tree, Oak, Pine, Ash, or Beech, influencing
and being accompanied by a peculiar undergrowth.

Compounds of the names of the dominant species are
used in naming the several associations, e.g. Heath associa-
tion, Ash wood association, Oak-Birch-Heath association,
Alder-Willow association, &c.

Plant-associations contain within them a number of
smaller communities, the plant-societies. These consist
of species more or less related to each other as regards
periods of active growth, shoot-systems of varying heights
and shade-requirements, underground parts of different
kinds and at different depths, drawing upon different
constituents or tapping different layers in the soil. A good

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 will
make a few observations on soils.

CHAPTER XXVI

THE SOIL

Origin of soils. Sedentary and transported soils. — If we
examine a section of soil in a quarry, as in Fig. 212, we can
form some idea of its origin. At the surface is a dark layer
containing the roots of the plants forming the surface vege-
tation. Below this is a lighter layer, the subsoil, which
grades off into the hard rock beneath. Acted upon by the
atmosphere, rain, and frost, the upper parts of the rock have
been broken into fragments, the smallest particles being
nearest the surface and forming the soil. Such a soil has
been derived from the rocks below, and its surface layer has
been darkened by organic matter, chiefly the decaying
remains 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 which
the soil could have been formed. The soil is made up of
particles varying in size from fine grains of sand to pebbles
and even boulders, all more or less rounded and water-

Fig. 212. Section of Soil in a Quarry.

Fig. 213. Soil on Glacial Drift.

320

THE SOIL 321

worn. Everything is suggestive of an old river bed, and
such alluvium has been carried there by water. In many
places large areas are covered with similarly mixed materials ,
but more angular, and whose rocks are of different kinds.
These have been deposited by ice-sheets and glaciers, and
are known as glacial drift (Fig. 213). The soil in these
areas is not derived from the underlying rock, but from
material which has been carried from a distance. Such
soils are therefore called transported soils, and are often
very complex in character and liable to vary much even in
short distances.

Effect on growth of different soils. — In all cases we find that
the roots of plants occur mainly in the dark soil. Why is
this ? Do they find more available food there than in the
subsoil ? Test this by sowing a few seeds in pots, one
filled with dark surface soil, a second with sand, a third
with subsoil, and a fourth with clay, and compare the results.

Fig. 207 is from a photograph of such an experiment and
shows how differently they have fared, though all the other
conditions are the same. Those in the surface soil are
sturdy and healthy, in sand they have not grown so well,
while those grown in subsoil are very poor and starved, and
have evidently been unable to extract from it a suitable
amount of food ; the seeds in the wet clay failed to ger-
minate.

Composition of the soil. — As is shown by water-culture
experiments, the compounds which form plant food must be
soluble, and contain at least the elements oxygen, hydrogen,
nitrogen, sulphur, phosphorus, potassium, magnesium, cal-
cium, and iron. But we have seen that a plant obtains
carbon from the carbon dioxide of the air in sunlight, and
the other elements are absorbed by the roots in the form of
compounds such as are used in a culture-solution. Other
elements also occur, e. g. sodium, silicon, and chlorine, but
some of these are not essential to all green plants. A soil,

1296 X

322 ECOLOGY

therefore, for vigorous plant-growth, must contain these
necessary constituents, and it is from plant-remains in the
soil that much of this food is derived ; hence the greater
fertility of the surface soil. But surface soils vary consider-
ably both in physical properties and chemical constitution,
according to the proportions of sand, clay, lime, humus, or
organic matter they contain.

Samples of different soils should be obtained and the
properties of the different constituents studied. By means
of a few simple experiments many important facts may be
discovered.

Take a little garden-soil and weigh out 10 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 it for a short
time at ioo°C, and weigh again. Has more been lost ?
Finally, burn the soil and weigh again. How much has
been lost by burning ?

The part that burns away is organic matter, chiefly de-
caying remains of plants. Note the change in colour after
burning ; the dark soil has become ' terra cotta '. Ten
grammes of garden soil when air-dried lost 2-56 grammes
of water, and a further 0-33 when heated to ioo° C, and
lost o-88 of organic matter on burning. What is the pro-
portion of water to the humus in the soil ? Determine
this proportion in different soils.

Put some garden -soil into a jar of water and stir
thoroughly. Note the floating fragments of humus. Pour
off the muddy water into a large vessel and repeat the
washing until the water clears quickly. Allow the muddy
water in the large vessel to stand for a few days and notice
how long it takes to settle. Pour off the clear water and

1 The water-content will vary even in the same soil, being greater
on 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 little soil into a tube, add water, and shake.
Allow it to settle and note how the layers arrange them-
selves. 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 leaves
and stems. The part which settles slowly from the muddy
water is very fine and sticky like clay, but dark-coloured
with 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 it. 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 mould on the decaying parts of plants ?

Dark 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 de-
composed and converted into soluble inorganic salts, as
plants can only take up their food-materials in solution.
Hence a fertile soil must contain organic matter, must have
the means of decomposing it, and must possess a suitable
water-supply to dissolve the salts when formed.

Organisms in the soil and their work. — What are the agents
in the soil which act upon the organic matter ? Can we

x 2

324 ECOLOGY

isolate them from the soil, or induce them to grow on an
artificial food-substance, so that we may examine them ?
The following experiment enables us to do this :

Sterilize some water by boiling, cover it to keep out dust,
and allow it to cool. Thoroughly clean and sterilize, bj'
boiling, seven test tubes and three small dishes (Petri dishes
are the most 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 tubes
A, B, and C. Pour A into dish No. 1 and cover. Take a
little garden soil, sterilize part of it by baking, leaving the
rest untreated. Half-fill tubes D and E with sterilized
water and to D add a little baked soil and shake up. With
a sterilized pipette transfer a few drops of the muddy liquid
from tube D to E to dilute it. Pour several drops of this
into 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 diluted
soil-water into dish No. 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. 1
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 be
examined under the microscope, myriads of tiny rods or
bacteria will be seen moving in the liquid. These, together
with the moulds, are the living beings of the soil which
decompose the organic matter, and prepare an important
part of the mineral food which green plants take up in
solution. Culture No. 1 shows they were not present in the
boiled gelatine, and No. 2 shows that the bacteria in this
part of the soil were killed by baking.

THE SOIL

325

The organisms in the soil are very various and do dif-
ferent kinds of work. Some take up the work where others
leave off, and carry it a stage farther. Much oxygen is
used up in the process, and in consequence the air in the
soil is poorer in oxygen and richer in carbon dioxide than
the atmosphere above ; however, the supply of oxygen is
kept up by diffusion.

In addition to bacteria and moulds, other and bigger
organisms are at work, such as earthworms, millipedes,
centipedes, beetles, and the larvae of many insects, all acting
on the soil in complex ways. For example, the burrows of
earthworms serve as air- and water-channels and make it
easier for roots to penetrate ; while the worm-castings
contribute much to the fine dark soil on the surface, and
render it more soluble.

Nitro-bacteria and the origin of nitrates. — The process
called nitrification is an excellent illustration of the work
of soil-organisms. During the changes which take place in
the organic matter in the soil, owing to the action of one
set of bacteria, nitrogen and ammonia are formed. The
nitrogen escapes into the air and the ammonia is acted upon
by another bacterium and converted into nitrous acid.
This acid readily reacts with certain mineral substances in
the soil (e. g. carbonates) to form salts called nitrites. A
third group of organisms converts the nitrous acid into
nitric acid ; and the action of the free nitric acid on salts
of calcium, potassium, and sodium gives rise to compounds
like potassium nitrate (saltpetre), calcium nitrate (lime-
saltpetre) , and sodium nitrate (Chili saltpetre) . These com-
pounds are of great value to plants ; they are very soluble in
water, and therefore can be absorbed by the root-hairs ;
they are the only source from which most flowering plants
obtain their nitrogen.

The organisms which bring about these important changes
are called nitro-bacteria, and they differ from other organisms

326 ECOLOGY '

in being able to assimilate carbon dioxide in darkness. To
carry on their work, they not only need suitable mineral
food, but also free oxygen and moisture. Their action is
stopped by too dry a soil and by strong sunlight. From
this we sec why aeration of the soil is essential, and why
over-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 Pea family (Legu-
minosae) and a few others, such as the Alder and Sea Buck-
thorn. On the roots of these plants, tubercles are formed
(Fig. 256, 3 in) as a result of attacks by bacteria-like organisms
in the soil, which enter by the root-hairs and cause the
swellings. These organisms fill the tissues of the nodules
and are able to take up the free nitrogen of the air and con-
vert 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 virtue of this alliance, the
nodule-bearing plants are able to thrive in soils deficient in
nitrates. Such a union of organisms is called symbiosis (see
p. 356). 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 exception is found in insec-
tivorous plants, which are able to supplement their supply
of nitrogen from animals which they capture and digest
in peculiarly modified leaves (see p. 361).

Test for Nitrates. — Dissolve a little 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 of garden soil for nitrates. First dry the soil,
plug the tube of a funnel with cotton wool, filter paper, or
asbestos, and fill up with the dry soil. Carefully pour
water on it, and collect a small quantity of the water which
drops from the end of the funnel, and test for nitrates as
before.

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 varying proportions of

1 2. 3. 4. 5.

Fig. 214. Absorption of Water by Different Soils.
1, sand; 2, clay ; 3, surface soil ; 4, subsoil ; 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 aspect to the country. Still there is much over-
lapping, and very few plants occur which are unable to
exist in either kind of soil. The vegetation on deep, wet

RFACESOIL

1 1

CLAY SUB"

50IL

^•-*"

,•-?

AND

UJ f

5
,4

/ »

/
/

_j»

i
• f

i /

BRA

CKE(

1 PE

}£••

.v""'

,-v>«-

.,.»■'

|rt.-v

.\**"'

.»•»•'

.a*

*•*

0 1 2 4 5 6 7 8 9 10 11 12 15 14

« DAYS >

Fig. 215. Curves showing the Different Rates at which
Water ascends in Different Soils.

peat differs from both ; this soil is more exclusive, many
species being unable to subsist on it.

Properties of soils. — Different kinds of soil should be col-
lected and their 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,

THE SOIL

329

closing one end with muslin, as in Fig. 214. Tap the tubes
several times until the soil has settled down ; then put the
closed end into water, and note the rate at which the
water rises, marking each period with a strip of gummed

I. 3. 4. 5.

0 J
5
10
15
20
25
50
55
40
45
50

60
65

TO
75
80
85

90
9b

100

Fig. 216. Diagram showing
Amount of Water absorbed
by the Soils in Experiment
Fig. 214. — 1, surface soil; 2,
clay ; 3, subsoil; 4, bracken peat;
S, sand.

z*y

Fig. 217. Experiment to
determine the Rate of
Percolation in the Soil.

paper. Sow ten mustard seeds at the top of each tube of
soil and note when they germinate and how they grow in
the different soils.

Does the water rise at an equal rate in each tube ? In
which case does it rise highest ? How does the proportion

330 ECOLOGY

of humus affect (i) the height to which the water rises
and (2) the water-holding capacity of the soil ? Continue
the records for several days and plot the results in curves
as in Fig. 215. Notice how very slowly water ascends in
dry peat in spite of 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^ inches in
thirty-nine days. The diagram, Fig. 216, shows the
amount of water absorbed by the different kinds of soil in
this experiment.

Half-fill another set of tubes with similar soils, but in these
cases add 50 c.c. of water from above. Note and mark at
short intervals the rates of percolation (Fig. 217) of (1) fine
sand, and (2) fine sand mixed with humus. Collect the
water that escapes at the lower end of the tubes and notice
in each case (1) rate of percolation, (2) time of appearance
of the first drop of water from the bottom of the tube,
(3) amount of water which escapes in a given time, (4)
amount of water held by the soil, observing again the
effect 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
observations in connexion with our previous ones, we
are able to understand why dark soil is better for plants
than subsoil.

Make similar observations on cotton-grass peat. Note
that it is greasy to the touch. Test samples with litmus
paper and determine whether it is acid, alkaline, or neutral.
How do peat and humus compare in these respects ? Peat
is acid, humus is neutral or alkaline.

Weigh out 10 grammes of fresh bracken peat, dry it, and
determine the water-content ; then burn it and weigh again.
How much is lost by burning ? Ten grammes of bracken
peat contained 66-2 % water, 17-4 % organic matter, and
i6'4 % mineral matter.

THE SOIL 331

Peat, like clay, holds much water ; it is therefore badly
aerated, and root-respiration is difficult. Further, it con-
tains little mineral food and a great excess of organic
matter ; and in addition it is acid or sour. No wonder,
then, that it is a poor soil for plants, or that so few species
grow on it.

Calcareous soils. — Chalk and Limestone soils. In a
soil derived from chalk or limestone, carbonate of lime is
always present. These soils support a vegetation differing
in many respects from that growing on soils deficient in
lime. The presence of lime in soils may be determined as
follows :

Take 5 grammes of chalk soil, boil it in water, and pour
oh the liquid. Repeat this two or three times and so
remove the soluble calcium salts (sulphate, chloride, and
nitrate). Drain off the water or press between filter paper,
and to the residue add dilute hydrochloric acid (1 in 10
parts of water). Note if there is any effervescence ; if so,
it denotes the presence of a carbonate, e. g. of magnesium,
lime, or iron. If the gas is copious it may be led into lime-
water and tested. What gas will it be ?

Filter off the insoluble matter and add ammonium
hydrate in slight excess to the filtrate. Filter off any pre-
cipitate which may result (e. g. iron or alumina) and add
ammonium oxalate. Is a white precipitate formed ?
If so, it is calcium oxalate. Thus it is shown, not only that
the soil contains a carbonate, but which specific one it is,
namely, calcium carbonate.

Rain-water carries with it into the soil carbon dioxide,
which has acid properties, and which, acting on the calcium
carbonate, dissolves it, so that a soil over limestone may
become relatively poor in lime, except for fragments of lime-
stone rock in the soil. This denudation of mineral salts
from a soil, and its consequent impoverishment, is called
' leaching '.

332 ECOLOGY

Effect of liming clay soils. — 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 ' sour '. The addition of
lime lessens these defects. Two very simple experiments
will show us the effect of lime on clay :

(i) Stir up a little clay in water ; the very fine particles
remain indefinitely in suspension. Add to the muddy
liquid a little lime-water and note its effect. The particles
run together in fluffy-looking masses and soon sink to the
bottom, leaving the liquid clear.

(2) Bend two pieces of gauze each into the shape of a
saucer or shallow cup and line them with wet clay. Pour
lime-water into one and tap-water into the other, and place
each on the top of a tumbler. Does the clay hold both
liquids equally well ? The tap-water does not percolate,
but the lime-water permeates the clay readily and changes
its properties. It becomes less sticky ; it has clotted and
become more porous, and it is no longer able to hold water.
Other salts and mineral acids have a similar effect, and as
lime also neutralizes the organic acids in a sour soil, we see
that its effects are threefold : it renders the stiff, unwork-
able clay more workable, improves its drainage, and, as the
farmer says, ' sweetens it ' by neutralizing the organic acids.
Clay is also rendered more pervious by mixing with humus.

State of the water in the soil : capillarity. — How water
ascends in the soil. Previous experiments have shown
that water ascends higher in loam than in sand, and
higher still in clay. Microscopic examination shows that,
of the three, sand consists of the coarsest particles, clay the
finest, while loam is intermediate. The larger the grains,
the greater will be the spaces between them. Will this
in any way affect the power of a soil to absorb water, and
if so, how ?

THE SOIL 333

Make a few fine tubes of different diameters by heating
a piece of soft glass-tubing in a flame and drawing out
portions to the thickness desired. Dip the ends of these
into a coloured liquid and note how high it rises in each case.
The liquid wets the inside of the tube and creeps up it,
forming a concave surface film. The pull which this film
exerts is proportional to the line of contact with the tube.
As we reduce the diameter of the tube, we not only reduce its
capacity, but at the same time reduce the pull, though we
see that in such a narrow tube it will support a much
higher column of water. In a wide tube the water rises
very little. This property of the ascent of water in narrow
tubes is called ' capillarity '.

Apply this principle to the different soils. Sand with its
coarse grains and large spaces will correspond to the widest
tube, loam to the intermediate one, and clay to the finest.
The capillarity of humus is greater still.

From these observations we see that water is present in
soils in different states :

(i) That which fills the free spaces, and, when in excess,
displaces the air.

(2) That which is still retained in air-dried soil, and may
be driven off at a high temperature.

(3) What may be called capillary water, which forms films
over the particles in the soil and on the roots of plants,
behaving similarly to that noticed in the capillary tubes.

The first readily drains away in a loose permeable soil ;
the second, which is called the hygroscopic water, is held
firmly by the particles and is of no use to plants ; the third
is the most important, because it is able to move in the soil
from wet to drier parts in any required direction, so that
the effect of absorption by root-hairs is to provide a space
into which more water is drawn by capillarity. By this
means, water may be drawn upwards in the soil eight to
ten feet.

334 ECOLOGY

In the case of trees with a wide-spreading root-system
and very large leaf-surface, the amount of water drawn
from the soil and given up to the atmosphere as vapour is
enormous, and has an important effect in drying the
soil and in increasing the humidity of the air. It is esti-
mated that, during one season, a Beech wood gives off
354 tons of water per acre, and that suitable trees planted
in marshy ground play an important part in draining it
and bringing it ultimately into a state suitable for higher
cultivation.

If the mineral 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 by
noting the difference of residue after evaporating (a) rain-
water, 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. By means of these changes soluble com-
pounds like salts of potassium, magnesium, calcium, or
ammonia displace the alkali in the silicates of the soil and
insoluble compounds are formed, and for a time fixed in the
soil. The next changes result in these insoluble compounds
being slowly acted upon and re-converted into soluble sub-
stances which provide a steady supply of mineral food for
plants.

In this manner the soil is constantly storing up plant-food
in an insoluble form, preventing its escape, and then giving
it up slowly to the plants in a soluble form. It is impor-
tant, however, that the solutions should be very weak, for
if they exceed a concentration of 3 % the plants are unable
to absorb them.

Effect of 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 evapora-
tion, so that a hoed soil is cool and moist and therefore
better adapted to plant-requirements. When the ground
is covered with vegetation this receives the sun's heat, the
soil is screened, and its temperature does not rise so much
as that of bare soil.

Factors affecting the water-supply in the soil. — From our
previous observations we have seen that any factor which
tends to modify the water-supply of a plant will affect its
growth. 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 of
heat, 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 moisture present determines the

rate of transpiration.

(3) The oxygen of the air is necessary for respiration

both by roots and shoots, and aeration of the
soil is essential.

(4) Carbon dioxide is necessary for photosynthesis by

green plants.

3. Wind. Moving air, by increasing the volume affecting

a given surface, increases evaporation ; hence the
drying effect of winds. The rate of transpiration is
great in plants having large thin leaves with sto-
mata on both surfaces, while it is reduced to a
minimum in plants with small rolled leaves with
stomata only on the enclosed surface, and therefore
in a ' still air ' chamber.

4. Precipitation. As plants must obtain their mineral

food in a weak solution, water is essential as a solvent

336 ECOLOGY

and diluent. It is obvious, therefore, that a suitable
water-supply is the most important edaphic or soil
factor. Water carries into the soil gases from the
air, one of which, carbon dioxide, gives to water
the power of dissolving part of the mineral matter
of the soil, e.g. potash and lime. On the physical
character of the soil depends the amount of water
available for plants. The rainfall of a district will
play an important part in determining the character
of the vegetation.

We generally 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. Plants
growing in a wet soil may possess structures 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,
it is said to be ' physiologically dry '.

CHAPTER XXVII

PLANTS OF HEDGEROWS AND WALLS

Uses and distribution of hedgerows. — Hedgerows provide
endless material for the study of plants and offer numerous
problems for solution. They are, however, fences intro-
duced by man and not a natural feature of the vegetation
of a country. Hedges are useful in many ways. They
protect the crops and surface soil from the drying and tear-

PLANTS OF HEDGEROWS AND WALLS 337

ing effects of the wind ; they lessen the rate of evaporation,
and in consequence help to maintain a higher temperature.
To render them more effective, spiny shrubs like the Haw-
thorn are generally selected, and large trees such as Oak,
Elm, Sycamore, Ash, and other forest trees are introduced
at intervals to provide shelter for the cattle. So numerous
are the trees that, when viewed from a distance, their
appearance is that of an open wood. Under the shrubs and
trees wild plants establish themselves, especially woodland
species, which are well suited to the shade of the hedgerow.

Hedges are not of universal occurrence. They are
absent from the uncultivated, sandy wastes and salt-marshes
of our shores, and they are not found on our moorlands
and mountains. They accompany man in his farming
operations, but even here they have a peculiar distribution.
In areas over sandstones and limestones, where the soil
is shallow and the ground often stony, they are replaced
by stone walls. On the other hand, in wet, low-lying fen-
districts the ' fences ' commonly take the form of ditches
and drains. It is in better-drained areas and often over
deeper soils that hedgerows predominate. Hence their
geographical distribution is significant. Hedgerows are
also essentially English, and give a character to the land-
scape without parallel in any other country.

Habitats of the hedgerow. — In a common type of hedgerow
the shrubs and trees are planted on a bank, below which
is either a ditch or a moist hollow, and beyond this is a
grassy sward. Thus in a very limited area are the follow-
ing distinct habitats : (1) Under the shrubs, shade, pro-
tection, and a soil containing much humus. (2) On the
hedge bank, a well-drained, more exposed slope. (3) At
the bottom either a ditch filled with water or a wet hollow.
(4) A drier, flat, miniature meadow. In each situation
characteristic plants occur, showing many interesting bio-
logical features. Note how numerous are the plants with

1296 V

33«

ECOLOGY

Q
OS
<

W
O
D
W

33
H

00
w

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 indicate
on it the species met with, as in Fig. 218.

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 ; branch-
systems ; bark of trees ; winter-buds ; protection ;
leaf-scars.

Spring. — Nature of bud-scales ; opening buds ; folding
of leaves and their modes of growth ; spring tints ;
characteristics of spring flowers ; wind-pollination ;
plants with storage organs, tuberous roots, rhizomes,
bulbs.

Summer. — Leaf-mosaics ; comparisons of stems and
leaves ; flowers and their insect-visitors.

Autumn. — Fruits and fruit-dispersal ; autumnal tints ;
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 :

(1) Shrubs with thorns and prickles :

(a) branch-spines — Hawthorn (Fig. 219, 1), Black-

thorn, Gorse.

(b) prickles — Roses, Brambles, Gooseberry (prickles

on the leaf-base).

1 The Barberry has two kinds of shoots : (a) long shoots bearing
leaves reduced to branched spines (Fig. 219, 2 and 4, l.s) ; in the
axils of these arise (b) dwarf shoots (Fig. 219, 2, d.s) bearing several
simple foliage-leaves, each having a joint near the base (Fig. 219,
3. ;')•

Y 2

340

ECOLOGY

(2) Plants with nectaries on their leaves (extra-floral
nectaries) : Guelder Rose (Fig. 219, 5), Bird Cherry,
Wild Cherry (Fig. 219, 6), and Bracken.

Fig. 219. Modified Shoots and Leaves. — 1, Hawthorn ; 2,
Barberry ; 3, base of Barberry leaf ; 4, spiny leaf on long shoot
of Barberry ; 5, leaf of Guelder Rose ; 6, leaf of Cherry ; 7, shoot
of Cleavers with hooked fruits ; b.s, branch-spine ; d.s, dwarf
shoot ; j, joint ; l.s, leaf-spines ; n, extra-floral nectaries ; st, stipule.

(3) Climbing plants :

These are very numerous, and all the main forms
may be found and their modes of growth observed.

(a) Hook climbers or Scramblers. Brambles,
Cleavers (Fig. 219, 7).

(b) Root climber. Ivy (Fig. 222, 1).

PLANTS OF HEDGEROWS AND WALLS 341

(a) to right or left indifferently — Woody Night-
shade. (Also by means of its leaf-stalks.)

(b) clockwise (i.e. left to right or with the sun)
— Hop, Black Bryony (Fig. 90), and Honey-
suckle.

(d) Sensitive organs (tendrils) :

(a) Branch tendrils — White Bryony (Bryonia
dioica) (Fig. 91).

(b) Leaf-stalk tendrils — Clematis (Fig. 92).

The Ivy is well adapted to the conditions of life in a
hedgerow or wood, and possesses many points of interest.
If its long slender branches spread out on the ground the
leaf-blades face upwards. Commonly the branches climb
the trunks of trees by pressing their groups of adventitious
roots into irregularities of the bark, where they adhere
firmly and serve as holdfasts (Fig. 222, 1). The leaves arise
spirally on the axis, and in their broad bases the buds
are partly embedded. The leaf -bases are sensitive motile
organs, and a very slight movement in this region carries
the blades at the ends of their long stalks through a wide
arc 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 tips all point downwards. The upper surface of
the blade is glossy and concave, and the drainage-channels
are directed towards the apex, which serves as a ' drip-tip ' ;
thus rain and snow quickly drain away. Observe the
behaviour 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 five
rows as before, but being illuminated on all sides the bases
do not bend, and the blades are not all directed to one
side (Fig. 222, 3) ; they are also smaller and simpler in
outline. In October or November these shoots produce

Fig. 222. Ivy. — 1, climbing shoot ; 2, section through leaf-base,
showing embedded bud; 3, flowering shoot; 4, flower-bud; 5,
flower seen from above ; 6, flower in side view ; 7, vertical section
of flower ; 8, fruit ; a.r, groups of adventitious roots ; b, bud ;
d, disk ; Lb, leaf -base ; p, petals ; s, sepals ; st, stem.

umbels of flowers (3), which possess several peculiar 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

PLANTS OF HEDGEROWS AND WALLS 343

the petals and are proterandrous. The pistil is inferior,
and consists of five carpels enclosed in a disk which becomes
fleshy ; the fruit is a berry (8).

Woodland species are so numerous in the hedges that
hedgerows may be regarded as linear extensions of the
woodland flora. The more typical herbaceous species are
Bracken (Pteris aquilina) and other ferns, Soft-grass and
other woodland grasses, Bluebell, Garlic, Purple Orchis,
Dog's Mercury, Moschatel, Anemone, Wood Violet, Wood
Sorrel, Primrose, Cowslip, Stitchwort, Herb Robert, Dead-
nettle, Hedge Woundwort, Foxglove, Crosswort, Jack-by-
the-hedge, Chervil, and Nettle.

Invaders from the meadows are represented by the
Daisy, Yarrow, Clover, and cultivated grasses ; while
wind-dispersed composites like the Dandelion, Groundsel,
Goat's-beard, and Thistles are also common.

Parasites are frequent, and we may find the strange-
looking Toothwort, which lives parasitically on the roots
of trees and shrubs ; also Broomrapes on the roots of her-
baceous plants (p. 359), or the Dodder (Figs. 230 and 231),
twining round and absorbing food from the stems of Gorse
or Clover.

The vegetation of the ditch varies with the water-supply.
If much water is present, aquatic and marsh species occur,
similar to those found in a pond and on its margin. Common
species are Mud Crowfoot [Ranunculus Lenormandi), Lesser
Spearwort (R. Flammula), Marsh Marigold (Caltha palu-
stris), Water Cress {Radicula Nasturtium), Bog Stitchwort
(Stellaria tdiginosa), Water Blinks (Montia fontana), Water
Starwort (Callitriche stagnalis), Square-stemmed Willow
Herb (Epilobium tetragonum), Water Dropwort (Omanthe
crocata), Brooklime (Veronica Beccabunga), and Floating
Mead-grass (Glyceria fluitans) .

In addition to the above, many other problems may be
studied in a hedgerow, e.g. how patches of bare soil or

344 ECOLOGY

disturbed ground become covered by plants. The first to
invade and colonize the ground are annuals with good
seed-dispersal mechanisms ; these are in turn succeeded
by perennials, many of which have effective means of vege-
tative propagation. The effect of shade and of exposure
on plant-distribution is obvious when we note how numerous
are the species on the sunny side, and how few on the shady
side, of a hedgerow. Similar differences may be seen in
hedgerows on opposite sides 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 is
often the case in areas covered with glacial debris and where
stones of various shapes and sizes are abundant in the soil.
When the land is brought under cultivation, the stones are
removed and used for building walls, often of great thickness.
The interstices are filled with small stones and earth, form-
ing a soil which is very porous, and from it the water soon
drains away. Seeds which are deposited in the crannies
by the wind or animals may germinate, but as the plants
grow they are liable to suffer periodically from drought.
It is usual to find, therefore, that plants which succeed in
such a habitat are provided with devices to reduce tran-
spiration ; the leaves are either very small or arranged in
rosettes, and often modified as water-storage organs. Many
of the species are familiar as rockery plants, e. g. fleshy-
leaved forms like the Stonecrops, Saxifrages, and Wall
Pennywort (Fig. 221) . Heaths, Hair-grass, Gorse, and Broom
have reduced and wiry leaves. The Ivy-leaved Toadflax
has slender trailing stems and fleshy leaves ; the stalks of
its ripening fruits bend away from the light, lengthen, and
carry the capsules into the crannies, where the seeds are
shed. The Ferns found growing on the wall are all hardy
kinds, e. g. Wall-rue, Black Spleenwort, and Polypody.

WOODLAND PLANTS 345

CHAPTER XXVIII
WOODLAND PLANTS

Features to observe in the study of a wood. — The vegetation
of woods varies considerably in different localities, accord-
ing to elevation, 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 should
be made to answer the following questions and to make
the following observations :

(1) Which is the dominant species of tree : i.e. which
species is it that on the whole makes its influence most
apparent ?

(2) What are the subordinate trees ?

(3) Does their arrangement or the character of the species
suggest 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 distribution influenced in any way by the
overshadowing trees ?

(7) Compare the shade produced by the different species
of trees, especially that of Beech, Elm, Pine, Oak, Common
Ash, and Birch.

(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
Birch (light -demanders) ?

(9) Compare the parts closely planted with the more
open parts.

(10) What is the nature of the soil, (a) siliceous or cal-
careous, (b) coarse, stony, shallow, and dry, or fine-grained,

346 ECOLOGY

deep, and moist ? (c) Is the soil covered with humus, and
if so, to what depth ?

(n) What is the aspect ? and how is drainage affected
by slope, dip of the rocks, or other causes ?

(12) If differences are met with in these respects, do you
find accompanying changes of species ?

(13) If the wood contains a wet hollow or if a stream
runs through it, compare the plants (both trees and
undergrowth) of the wet parts with the drier parts of
the wood.

(14) Compare the undergrowth of the wood with that
of adjacent fields. To what extent are the species
similar ?

(15) How will such a comparison help to decide between
(a) a recent plantation and (b) an old wood ?

Select a typical piece of woodland and mark out a narrow
strip across it, as indicated in Fig. 223, 1, a to b. This may
be subdivided into convenient squares and the parts studied
along the lines indicated. Afterwards a more extended
study may be made, and the results recorded on compara-
tive maps, as in Fig. 223, 1, 2, and 3, of which 1 is a tree map,

2 a map of the common plants of the undergrowth, and

3 a soil map.

From studies of this kind, we learn that, by a combina-
tion of factors such as increased shade, a moister atmo-
sphere, more humus in the soil, a more regular water-supply
to the plants, and protection by the overshadowing trees,
an assemblage of plants is met with in a wood which differs
in many respects from the adjoining 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 deter-
mined by soils, water- supply, and the other above-named
factors.

WOODLAND PLANTS

347

Dry and moist Oak woods.— Fig. 223, 1 and 2, are maps
showing the vegetation of a wooded escarpment with
siliceous soils. Fig. 223, 3, is a soil map of the same wood.
Note the form of the escarpment as indicated by the

rrOAH

UPlNE
• •BEECH.

.VHEATWPLKN-nj
HII BRACKEN.
'•■■■- SOFTGRftSS.
U.1:lSOrTGRASS-P.Rf>,C«EN

-Bluebell society

•••shallow

SftNOy PEAT.
|:IH STONyDEBUl
I l IIHUMUS OV£R

TINE. LOAM

Fig. 223. Comparative Maps of a Wood. — 1, showing distribution
of trees ; 2, undergrowth ; 3, soils.

contour lines. The highest part of the wood has a shallow
soil of sandy peat resting on millstone-grit sandstone ;
the latter is coarse-grained and jointed, and thus permits
rapid drainage (see Fig. 212). The steep slope is covered

348 ECOLOGY

with stony debris and washed-down material from the
weathered sandstone edge. This debris rests upon a bed
of 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 and
moister soil formed from the shales, and is covered by
humus several inches in thickness.

The dominant tree is the Sessile Oak, the subdominant
ones Birch and Scots Pine, with occasional trees of Moun-
tain Ash, Holly, and Hawthorn. There is also a small
group 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 abun-
dant, has thick hard leaves. A little lower, on the stony
slope, Ling is less abundant, Hair-grass and Bracken are
dominant, and there is also Bedstraw, Tormentil, Cow-
wheat, &c. In the lowest part, where the soils are deeper
and 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 adjoining portion of the wood occur
such trees as Alder, Willow, and Bird Cherry, as well as
the characteristic trees of the wood, while the ground flora
consists of Marsh Marigold, Bitter Cress, Lady's Smock
or Cuckoo Flower, Greater Stitchwort, Marsh Stitch wort,
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 back-
rolled 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 charac-
teristic of the drier and more exposed parts. We observe,

Fig. 224. Oak Wood in Summer.

318

Fig. 225. Oak Wood in Spring. — Ground flora of
Soft-grass, Bracken, and Bluebell.

Vic *r^ |A' M

Fig. 226. The Sulphur Tuft Toadstool (Hypholoma
fascicularis) growing on Decaying Wood.

34c

WOODLAND PLANTS 349

also, that while some species are restricted in their distri-
bution, others (e.g. Bracken) are much more plastic, and
persist in very varied habitats.

In the typical moist Oak woods on siliceous soils the
above-mentioned species, along with many others, occur,
and the ground flora is often a bright flowery carpet.

Ash woods on calcareous soils. — In woods on calcareous
soils the ground flora is still more varied. Oaks are rare,
the Common Ash tends to occupy the first place, accom-
panied by shrubs like the Hazel, Wayfaring Tree, Spindle
Tree, White Beam, Buckthorn, Dogwood, and Privet.
Among the herbaceous plants the Dog's Mercury is a very
abundant social species covering large areas. Others com-
mon or frequent are Primrose, Cowslip, Wood Crane's-bill,
Blood Crane's-bill, Avens, Strawberry, Great Burnet, Stone
Bramble, Spurge Laurel, Hellebore, Small Scabious, Lily-
of-the-Valley, Solomon's Seal, several Orchids (e.g. Tway
Blade, Helleborines, and Purple Orchis), False Brome-
grass, and Brittle Bladder Fern. The Bracken is usually
inconspicuous and often absent. Thus Oak woods on
siliceous soils and Ash woods on calcareous soils form two
well-recognized types of woodland.

As we have seen, woodland species extend along the
hedgerows, and reference should be made to the groups of
plants mentioned in Chapter XXVII for further examples,
especially of climbing and scrambling plants, whose natural
habitat is the woodland.

If we take a general view of the plants in a wood we see
at once that they tend to occupy successive layers. The
highest is the tree layer, below which is a layer of shrubs,
and lower still are layers of tall, intermediate, and low-
growing herbaceous plants (Fig. 224).

With such a succession of overshadowing layers it is
obvious there must be considerable accommodation among
the different species. To watch these layers throughout

350 ECOLOGY

the seasons forms an interesting study. In the winter, tree
and shrub layers stand out in sharp contrast, as in the case
of leafless Oak and evergreen Holly. Still more striking
is the spring aspect of Ash and Hazel, the early bright-
green 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 in
the spring by low-growing plants (Fig. 225) like the Blue-
bell, Anemone, Primrose, 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 societies. — The diagram (Fig. 227) will
help us to appreciate the significance of such adaptations
in the ground flora of an Oak wood where the three plants
illustrated commonly grow in close association. In the loose
leaf-mould on the surface run the rhizomes of the Soft-grass.
Beneath this, in the dark soil containing much humus, are
the rhizomes of the Bracken, while in the fine yellow loam
below are the bulbs of the Bluebell, though young bulbs
on their way downwards may be found in the other two
layers. In November the young green blades of the Soft-
grass appear, and through the winter and early spring form
a bright green carpet. Meanwhile, the leaves of the Bluebell
come above ground, to be followed in the early spring by
a wealth of flowers (Fig. 225). Towards the end of the
flowering period, and as the fruits are ripening, the Bracken
unfolds its fronds, and raised on tall stalks above the tops
of the young Bracken are the flowers of the Soft-grass.
In the late summer and autumn the mature Bracken-fronds
form a continuous cover. Eventually they die down to
form a warm winter carpet. Thus their soil-requirements,
their modes of life, their periods of active vegetative
growth, their times of flowering and fruiting, are for the

Fig. 227. Complementary Society in an Oak Wood.
a, Soft-grass ; b, Bracken ; and c, Bluebell.

352 ECOLOGY

most part different. Species growing mutually together
in this way form a complementary society. Reference
to the maps (Fig. 223, 1 and 2) will show that these three
species do not always grow together. In places you will
hnd that one may grow to the exclusion of the others.
Under the deep shade of the Beech, the Bracken seldom
occurs, 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 British woodlands. — There is very little natural
woodland in the British Islands. Plantations are numerous,
and some of these, being on the sites of native woods, pre-
serve many of the features of primitive forest. The wood-
lands of Britain may be divided into two main groups,
namely :

(1) Woodlands on siliceous soils : clay, loam, and sand.

(a) Alder- Willow wood : a lowland type with a ground
flora of marsh-plants ;

(b) Pedunculate Oak wood, with a flowery carpet of
moisture-demanding species ;

(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 ;

(/) Pine wood : this type differs from the above de-
ciduous woodlands in being composed mainly of
evergreen coniferous trees.
Native Pine 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 Pine often
develop freely on heather moors, both lowland and upland,
and form a Pine-Heath wood. Many of the present Pine
woods are plantations, and exotic conifers are commonly

WOODLAND PLANTS 353

planted, e.g. Spruce, Douglas Fir, and Larch ; the latter,
however, has deciduous leaves (see p. 275). In addition
to the heath-plants the following interesting species occur
in old Pine woods : Winter-greens (Pyrola minor, P. media,
and P. secunda) and Cow- wheat (Melampyrum), which are
semi-parasites ; the Coral-root Orchid, a saprophyte (see
p. 357), and Chickweed Winter-green (Trientalis europaea).
(2) Woodlands on calcareous soils : marls, limestones,
chalk.

(a) Alder wood or Carr, with a ground flora of fen-
plants. The Alder is the dominant tree. Other
trees and shrubs are Sweet Gale, Creeping Willow,
Black and Red Currant, Berry-bearing Alder, Buck-
thorn, Guelder Rose, Common Ash, and Birch (B.
tomentosa). Common herbaceous species are : Marsh
Fern, Tussock Sedge, Yellow Iris, Nettle, Meadow-
sweet, and Marsh Marigold.

(b) Oak- Ash wood on marls. These woods are similar
in many respects to the peduncled Oak wood, but
have a more varied ground flora. Oak and Ash are
the dominant trees. The shrub flora is abundant,
and consists of Hazel, Wayfaring Tree, Spindle Tree
(Euonymus), Traveller's Joy, Dogwood, Privet, Field
Maple. The characteristic herbaceous species not
found in the peduncled Oak woods are Herb Paris,
Meadow Saffron (Colchicum), Gladdon (Iris foeti-
dissima), Dog Violet (V. sylvestris), Nettle-leaved
Bellflower (Campanula Trachelium), and the Orchids
Helleborine media and H. purpurata.

(d) Beech wood on chalk. Native Beech woods are
confined to the Chalk Downs of the south of England,
where they form ' hangers ' on the steep slopes.
The deep shade cast by the Beech tends to exclude

1296 Z

354 ECOLOGY

other trees and shrubs, and the ground flora is very
scanty (Fig. 190). The more common trees are
Gean (Prunus 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 the lighter parts,
are Dog's Mercury, Sanicle, Violets (V. sylvestris,
V. Riviniana, and V. hirta), Strawberry, Enchanter's
Nightshade, Helleborines, Large Butterfly Orchis,
and the saprophytes, Bird's-nest Orchis and the
Yellow Bird's-nest (Monotropa) ; also the Green and
Stinking 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 the
soil contain much organic matter, and are commonly covered
by the remains of plants which are the accumulations of
successive years of growth. In meadows and pastures, this
tangle of vegetable matter, living and dead, forms the
turf. In woods, we know it as leaf-mould or humus ;
and it is often many inches in thickness. On the moors,
it forms deep beds of peat. Examine the leaf-mould in
a wood, and, on lifting it from the ground, note that the
decaying leaves are often held together by a white, felt-
like mass of mould-threads. This felt is the vegetative
part of various species of Fungi and is known as the
mycelium. From this mycelium arise the fruit-bodies of
the Fungi, some of which we are familiar with as Mushrooms

PLANT-LIFE IN HUMUS 355

and Toadstools (Fig. 226). The threads (or hyphae) of
the mycelium obtain their food from the dead leaves and
other organic matter ; and, along with organisms like
bacteria, are responsible for their decay. The Toadstools,
therefore, live upon the complex organic substances of
dead leaves and twigs, or on animal remains and excre-
ments ; whereas the food of green plants consists of
solutions 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 to
absorb light-energy, and can thrive without developing
either leaves or chlorophyll.

Saprophytes, Mycorrhiza, and Symbiosis. — Plants growing
upon dead organic matter (animal or vegetable) are called
saprophytes (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 coil
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 tissues of the
plants. In return they receive shelter and possibly some
food from the roots.

Such a combination of fungal hyphae and the roots of
plants is called a mycorrhiza (Gr. mykes - a fungus,

z 2

356 ECOLOGY

rhiza = a root), and a very large number of plants which
grow in humus, trees and shrubs as well as herbaceous
species, have a mycorrhiza on their roots. These plants
have 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 directly 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 tree-
trunks, 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 supplies
them with mineral food, out of which the latter, by virtue
of their chlorophyll,, build up organic materials, which in
turn are absorbed as food by the fungus. We have already
noticed (p. 326) the case of symbiosis in leguminous
plants, where root-nodules are formed as the result of
the action of bacterioids which enter the root-hairs. The
Alder and Sea Buckthorn are further examples.

Plants that live entirely on humus or other dead
organic matter are generally lowly forms like Fungi, and,
as we have seen, have no need for and do not contain chloro-
phyll in their tissues. Some flowering plants grow in the
humus of woods and, like the Fungi, live entirely upon it.
Very few British plants are able to subsist in this way ;
some of them are Orchids, e. g. the Bird's-nest Orchid
(Neottia Nidus-avis) and the Coral-root Orchid (Corallo-
rhiza). Another, belonging to the heath family, is the
Yellow Bird's-nest (Monotropa Hypopitys), and all have
mycorrhiza on their roots or rhizomes.

PLANT-LIFE IN HUMUS

357

These plants have become strangely modified in conse-
quence of their saprophytic method of obtaining food, and
they possess several features in common with the Toad-
stools: (i) their vegetative parts are embedded in the
humus ; (2) they obtain their food from the complex organic
compounds of the humus ; (3) they contain very little
or no chlorophyll, and so are white, yellowish, or brownish
in colour ; (4) only their flowering and
fruiting shoots come above ground.
Under such circumstances green leaves
are not needed, and they are reduced
to mere scales.

The rhizome of the Bird's-nest
Orchid gives off into the humus a
tangled mass of underground stems
and roots which resemble a bird's
nest, hence its name. They are in-
vested with a mycorrhiza, the hyphae
of which are attracted to and enter
the absorbing cells. The Coral-root
(Fig. 228) does not develop roots at
all ; its rhizome (rh) is short and
much branched, and from it many
absorbing root-hairs are given off.

The Yellow Bird's-nest (Monotropa
Hypopitys) grows in the humus of
shady woods, and it was on this plant
that mycorrhiza was first discovered.
From its underground stem is given
roots which are covered with fungal hyphae, and these
provide food for the Yellow Bird's-nest from the humus
they are decomposing.

It is common for Fungi to live at the expense of green
plants, but it rarely happens that flowering plants are able
to live upon the labour of the fungus.

Fig. 228.

Coral-root Orchid.

rh, rhizome.

off a dense mat of

358 ECOLOGY

Parasites. — Not only do dead and decaying leaves
provide a habitat for many plants, but commonly living
plants (and even animals) provide habitats for many
species, especially Fungi. Familiar examples of this are
the rusts, mildews, and blights, which often destroy valuable
crops. A plant which lives at the expense of another
organism is called a parasite ; and the organism upon which
the parasite preys is known as the ' host '. The guest, how-
ever, is uninvited and takes advantage of the ' hospitality '
to the injury of the ' host ', and sometimes causes its death.

Living habitats are often selected by plants other than
Fungi, e. g. many flowering plants prey to a greater or less
extent on their neighbours. The most familiar example
is 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 the
branch, where they germinate. Suckers enter the branch
and form a union with the wood of the ' host ', from which
they draw the mineral food for the mistletoe. 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 entirely dependent on its
' host ' for food, and may be regarded as a partial parasite.

Many flowering plants are partially parasitic, and attach
themselves by means of suckers to the roots of neighbouring
plants, especially grasses. They produce green leaves and
closely 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 those
of the Louseworts are red or reddish-green.

A few flowering plants are entirely dependent on ' host '-
plants for food. Some of these, like the partial parasites
above mentioned, attach themselves by suckers to the

Fig. 229. Toothwort. —

1, part of underground stem ;

2, roots ; h.r, root of ' host '-
plant ; P.r, root of parasite ;
s, suckers attached to ' host ' ;
sc, scale leaves.

Fig. 230. Twining Stem
of Dodder attached by
Suckers to the Stem of
Hop.

Fig. 229 a. Section of Root
of Ling showing Mycorrhiza.

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. its

360 ECOLOGY

vegetative organs are underground, its leaves are reduced
to scales, only the flowering shoot comes above ground,
and the plant is a sickly yellow or purplish colour with
little or no chlorophyll in its tissues. The rhizome is thick
and bears four rows of curious scale-leaves (Fig. 229, 1),
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 slit at the base. Very small animals often
enter the cavities and die there, and the products of their
decay may be absorbed ; while special cells in the walls
of the cavities may serve for the excretion of water. The
roots form disk-like attachments (Fig. 229, 2 s) on the roots
of trees such as Hazel, Elm, and Beech, and suckers from
the disks enter the tissues of the host and absorb nutri-
ment ; it is also probable that some nutriment is absorbed
from the humus after the manner of saprophytes.

Several species of Broomrapes occur in Britain and are
parasitic on the roots of such plants as Broom, Gorse,
Clovers, Hemp, and Ivy. They are dirty white or yellowish
in colour, or tinged with pink and, like the Toothwort,
send only their 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 like
a tendril (Fig. 230). If it comes in contact with a ' host ',
it twines round the stem and sends a sucker or haus-
torium (Fig. 231) into it, and both the wood and the bast
of the haustorium form a union with the corresponding
tissues of the host. By this means the Dodder can obtain
the whole of the food it requires. The root now dies away,
and the slender stem, which is without chlorophyll and does
not bear any green leaves, subsists entirely at the expense
of the plant on which it preys. As new branches arise they

Q
W

<
to

# •
2 *

to u

° Q

H Z
Z &

< en

CM
n°

-■•

■ : ■■'

to1
>

o
j
O

Q
to O
O Q

H
C/3

to
O

H
CJ
W

H
K
H

to
O

t/3

W
«
o

C/)

> !»
I/l m

« to

£ w
to

,h to

360

INSECTIVOROUS PLANTS 361

spread over and twine around other stems ; and it 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 tiny
Convolvulus. Dodders {Cuscuta spp.) occur on a great
variety of plants, such as Clovers, Vetches, Flax, Hop,
Gorse, Ling, Bedstraw, Thyme, Thistles, and Nettles ; and
they may 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 their mode of nutrition.
The flowers show little or no modification except in colour,
and much of the energy they derive from the ' host ' is
expended in the production of an abundance of seeds.
Partial parasites and partial saprophytes are more common,
and show intermediate stages of modification according
to 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 cavities 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 into
the 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 Silene
have received in consequence the popular name of ' Catch -
fly '. 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 way
are known as insectivorous or carnivorous 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 chloro-
phyll in their tissues, and their general mode of nutrition
is like that of an ordinary green plant. The animal food
obtained by means of their traps is, therefore, only supple-
mentary. Still, their capturing devices are ingenious and
curious. They may take the form of : (i) sticky hairs or
sticky and sensitive tentacles ; (2) trap-like bladders and
pitchers; and (3) sensitive leaves which form rapidly-
closing traps.

Two examples, the Sundew (Fig. 232) and Butterwort
(Fig. 234, 1,2), are locally abundant in boggy places on
the moors, both in hilly districts and on lowland moors.
Three species of Sundew occur, the most common one
being the Round-leaved Sundew (Drosera rotundifolia) . It
is a small plant, only a few inches high, whose slender roots
anchor the plant in the wet soil, or among bog moss, and
the leaves form a rosette pressed close to the ground. At
the end of the leaf-stalk is a circular, reddish blade, fringed
with 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
if a small insect alights on some of the tentacles at the
edge of the leaf it 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 it is brought into
contact with other drops and eventually it is smothered
(Fig. 233). The secretion of the tentacles is now changed,
and a ferment is poured out which digests the protein
compounds of the insect's body, and these digested materials

INSECTIVOROUS PLANTS

363

are absorbed by the leaf, leaving only the indigestible
remnants, such as wings, hairs, and claws, on the blade.
After the ' meal ' the tentacles bend outwards once more
and again secrete the sticky and attractive, though
deceptive fluid.

In the plant photographed (Fig. 232) some leaves were
digesting food ; others had ' scraps ' and ' leavings ' on
them ; some were fresh and open, waiting for prey ; while
in the centre of the rosette the
youngest leaves were still un-
folded, like a tiny hand with
innumerable fingers tightly
closed.

The Butterwort (Fig. 234, 1)
has a rosette of radicle leaves
pressing so firmly against the
ground that when the plant is
taken up they bend sharply
backwards (Fig. 234, 2). Each
leaf is yellowish-green and
ovate, with its edges uprolled,
and the flowers, though different
in structure, resemble those of
the Wood Violet. The surface
of the leaf is greasy to the touch,
due to a secretion from glandular

hairs. Insects alighting on the leaf adhere to it, and
under the stimulus the edges may roll farther inwards
and more or less enclose the prey. A digestive ferment
is now secreted, and the products are absorbed as in the
Sundew.

In pools of the lowland moors, in stagnant ditches and
slow-moving streams or drains, a curious insectivorous
plant may be found with much-branched, thread-like, green
shoots, bearing on them numerous small bladders (Fig. 234,

Fig. 233. Leaf of Sun-
dew.— Tentacles on the
left curving as the result
of stimulation (Pfeffer).

364

ECOLOGY

Fig. 234. Insectivorous Plants. — 1, Butterwort ; 2, the same
showing leaves strongly reflexed when taken from the ground ;
3, branch of Bladderwort ; 4, bladder enlarged; 5, 6, leaves of
Pitcher-plants ; 7, leaf of Venus' Fly-trap, open ; 8, the same closed ;
bl, bladder; h, sensitive hairs; t, tendril.

INSECTIVOROUS PLANTS 365

3 and 4). These have suggested both the common and
scientific names for the plant — Bladderwort and Utricularia.
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 ', filled
with water and provided with ' doors ', which open only
from the outside. Small aquatic animals may enter, but
are 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 by
the bladder. The Bladderwort probably does not secrete
a digestive ferment and thus its mode of nutrition is that
of a partial saprophyte.

In the Indo Malayan region and elsewhere, a number of
bog-plants occur which have large and remarkable water-
pitchers, and many of these may be seen in hothouses and
botanic gardens. Fig. 234, 5 and 6, shows the leaves of
two of these Pitcher-plants, which are species of Nepenthes.
The midrib 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, projecting inwards and
fringed with sharp teeth. The outer surface is blotched
with various shades of red, brown, and green, and so is
attractive to insects. At the entrance are honey-glands,
and below them the surface is glazed and smooth, forming
a ' slide-zone '. On reaching this, insects find it easy to
descend into the water, where they are drowned. Digestion
is brought about by ferments secreted by the glands of the
pitcher.

Some pitchers are formed from whole leaves, as in the
Side-saddle Flowers (Sarracenia) of North America ; while
in Cephalotus, an Australian Pitcher-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 {Dionaea muscipula) (Fig. 234, 7 and 8), a plant
growing in mossy places in the woods of Carolina. Its
leaves, like those of the Butterwort, form a rosette close to
the ground ; the leaf -stalk is winged (phyllode), and the
blade, slightly bent upwards along the midrib, is fringed
with long, comb-like teeth. Many glandular hairs cover the
upper surface, and on either side of the midrib are three
long jointed 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 if 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 digested
materials are absorbed by the leaf. Later it expands in
readiness for more food.

The advantage to insectivorous plants of this mode of
nutrition is in the gain of nitrogen and nutritive salts sup-
plied with the nitrogen compounds, and the plants thus
supplied with animal food thrive better than those living
solely on inorganic materials.

CHAPTER XXX

GRASS-LANDS : PASTURES AND MEADOWS

A large part of the British Islands is devoted to pastur-
age, about one-half of England, three-quarters of Wales,
one-half of Scotland, and three-quarters of Ireland being
so utilized. Some of this is mountain and heath land, but
the greater part is permanent pasture dominated by grasses.

W
X
w

#
O

en
tit

Of
©
O

t/1
<

*66

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 habit, and great range of species suited to
very varied conditions, they form one of the most important
vegetation features of temperate regions, e. g. the extensive
pastures and meadows of Europe, the steppes of Russia,
and the prairies and savannas of America. They com-
monly form extensive carpets, as in our pastures and
meadows, and their numerous
leaves and the accumulated
remains of rhizomes and felted
roots form turf or sod.

Grass moors. — On the shaly
siliceous Pennine Slopes large
areas are dominated by grasses
(Fig. 235), two species being
especially conspicuous. The
Mat -grass (Nardus stricta)
(Fig. 236) in the summer
forms large tussocks with
grey -green, wiry, up -rolled
leaves (Fig. 255, 3) ; in the
autumn it turns a light yel-
lowish-brown, colouring the
mountain-sides and forming
a conspicuous feature in the
landscape ; it is easily recognized in the winter by
its one-sided empty spikelets.

Along with it, and often becoming dominant over con-
siderable tracts, is another tussock-forming species, the
Waved Hair-grass {Dcschampsia flexuosa). Its leaves are
still finer than that of the Mat -grass, and up-rolled so as to
leave only a very narrow groove (Fig. 255, 4).

The Bent (Agrostis vulgaris) and Sheep's Fescue (Fesluca
ovina) (Fig. 255, 2), both with up-rolled leaves, are very

Fig. 236. Mat-grass. — Part
of a tussock showing the
closely-packed shoots on the
rhizome.

368 ECOLOGY

abundant, especially at rather lower levels. Associated with
these in the drier parts are many heath-plants, e. g. Ling,
Cross-leaved Heath (Erica Tetralix), and Bilberry. In the
wetter parts of these grass moors the ground is occupied by
huge tussocks of the Purple Moor-grass (Molinia 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 calcareous
grass-lands of the hill-slopes of the mountain limestone and
the great sheep-grazing grounds of England, the Chalk
Downs. The Mat-grass, Waved Hair-grass, and Purple
Moor-grass are absent, and in place of their tussocks we
have a much shorter grassy turf dominated by the Sheep's
Fescue-grass (Festuca ovina), and with it the Lesser Meadow
Rue (Thalictrum minus), Lady's Fingers (Anthyllis Vulne-
raria), Horseshoe Vetch (Hippocrepis comosa), the Lesser
Burnet (Poterium Sanguisorba), the Rock Rose (Helian-
themum Chamaecistus) , the Lesser Scabious (Scabiosa Colum-
baria), and the Hoary Plantain (Plantago media), 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 types
of 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 (Dactylis 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.

Meadows. — Because of their higher cultivation, meadows

GRASS-LANDS : PASTURES AND MEADOWS 369

possess fewer species than pastures ; the grasses are com-
monly of species introduced by man, and since these are
grown as a crop, relatively few other species occur. In a
pasture, however, which in hilly districts may never have
been under the plough, we have a greater variety of wild
grasses together with a considerable number of flowering
plants. In either case the species will tend to vary according
to changes of soil, water-content, or other factors.

Survey of a pasture. — Examine a pasture, one with some
variety of surface for preference, and select a line passing
through typical parts of it. Study the plants along this line
and note also any differences which occur as to changes of
slope, soils, and their water-capacity, and drainage. Do
you find any indication of change of species which corre-
sponds to change of conditions ? Compare the plants of
the drier, well-drained parts with those of wetter parts, and
notice any peculiarities in habit and form of leaf. Do the
species persist throughout and under all these conditions,
or are some more restricted in their distribution ? Draw
to scale a plan of the field ; indicate changes of level by
contour-lines, and mark on this plan by means of signs the
more characteristic plants as they occur. A small field
studied in this way has a steep slope marking the outcrop of
a bed of sandstone ; the lower part is flat, lies over a bed of
shale, and is ill-drained and damp. This pasture is bounded
above by a Hawthorn hedge, beneath the shade of which
are woodland plants, e. g. Bracken, Male Fern, Bluebell,
Anemone, and woodland grasses. The steep slope is
covered by a sandy loam, and the fine, rolled-leaved Hair-
grass is so abundant as to give a distinct aspect to the slope.

Careful examination shows that many other species
grow along with it, such as Lady's Bedstraw, Tormentil,
Purging Flax, Speedwell, Mouse-ear Hawkweed, Sheep's
Sorrel, White Clover, Field Rush, Narrow-leaved Plantain,
Mouse-ear Chickweed, and a few plants of Eyebright and

i29G a a

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 different.
The rolled-leaved grasses are displaced by grasses with
larger 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 like Wild Thyme,
Yellow Violet, Lady's Fingers, Burnet, Yellow Bedstraw,
Small Scabious, Hoary Plantain, 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. 237). At the inlet,
look for the stages in the development of a marsh, and
notice how invasion of the pond takes place (Fig. 238).
Draw a transect, e. g. Fig. 239, through the pond, including
a portion of the bank, and show in a diagram the succession
of plants met with. The upper part of the bank (a) is
covered by meadow-species, but near the wetter soils be-
low (b), these give place to Rushes, Purple Loosestrife,
Water Dropwort, Iris, Marsh Marigold, Lady's Smock,
Large Bitter -cress, Bog Stitchwort, Ragged Robin, Meadow-
sweet, Lesser Spearwort, and Bog Starwort.

Nearer the water's edge is a belt of reed-like plants (c),

Fig. 237. Water-plants invading a Lake.

Fig. 238. Marginal Vegetation of a Pond; Water
Buttercups extending far into the Water.

37°

WATER AND MARSH PLANTS

37i

many with erect strap-shaped leaves, such as Iris, Bur-reed,
Flowering Rush, Arrowhead, the Reed Poa or Mead-grass
(Glyceria aquatica), and the Common Reed (Phragmites).
The last named is a good indicator of the direction of the
prevailing winds ; it has smooth leaf -sheaths, and all the
upper exposed blades turn round in the direction in which
the wind is blowing (Fig. 240).

Extending farther into the water (d) are the Smooth
Horsetail, Water Plantain, and Mare's-tail. Usually these

Fig. 239. Transect of a Pond.

avoid complete submersion, their upper parts growing
above the surface of the water. They are closely followed
by species like Water-Lilies (e), Water Buttercups, Floating
Mead-grass (Glyceria fluitans), and some Pond-weeds
which, though rooted in the mud, have some leaves in
the water, and others (usually of a different type) floating
on the surface.

In the Water Buttercups the submerged leaves are
dissected (Fig. 242) ; the floating leaves are entire. Sub-
merged leaves of the Water-Lily are large and very thin,
while the floating leaves are thick, and covered on the upper

a a 2

372 ECOLOGY

surface by a leathery cuticle (Fig. 241). Plants like these,
which bear different kinds of leaves, are said to be hetero-
phyllous (Gr. heteros = different). Heterophylly is common
in water-plants and frequently occurs in land-plants.

The Frog-bit has floating leaves and much-branched
roots hanging in the water, but often not rooted in the soil
(Fig. 239, e). The Duckweeds, with their curious leaf -like
stems (phylloclades or cladodes) and roots hanging in the
water, are entirely floating. In the more open water many
plants occur which are rooted and entirely submerged,
e. g. Water Milfoil, Canadian Water-weed, Stoneworts, and
many Pond-weeds; while plants like the Bladderworts
have neither root nor floating leaves, but are suspended
unattached in the water.

Growing among these is 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 single
microscopic cell, exhibiting, as in the case of desmids and
diatoms, structural details which are both elaborate and
beautiful.

Structural peculiarities of water-plants. — Specimens of
the different types of water-plants should be obtained,
and their varied forms studied with especial reference to
their aquatic surroundings, on account of which water-
plants form a distinct type of vegetation.

Cut sections of stems and leaves of the larger species and
examine them with a lens. Note that the bulky cortex
contains very large air-spaces (Fig. 243), and these occur
not only in stems and leaves, but also in the roots. The
roots growing amongst decaying organic matter, and in
badly-aerated mud, are thus able to obtain a supply of
air by diffusion from the shoots above. The vascular
bundles of the stem, as in roots (Fig. 15), are often
concentrated in the centre, which is a good position for
resisting the longitudinal strain of running water. The

In the foreground Arrow-

Fig. 240. Water-Plants in a Ditch.
head, and beyond the Common Reed with leaves indicating the
direction of the wind.

Fig. 241. Floating Leaves of the Yellow Water Lily.

372

WATER AND MARSH PLANTS

373

woody tissues are so poorly developed that many water-
plants collapse when taken out of the water, showing how
dependent they are on water for mechanical support.

The position and mode of growth of the underground
stems and roots, even in the same species, vary considerably,

Fig. 242. Water Buttercup.
a, Submerged leaves; b, floating leaves.

Fig. 243. Transverse Section of Leaf of Flowering
Rush, showing large Air-spaces.

and are determined largely by ' water-content ' in the soil,
and the supply of oxygen. The rhizomes and roots are
often placed more or less horizontally, and in this position
are near to the air-supply. As the soil becomes drier and
better aerated, the roots take a more vertical course.
The stems and leaves of water-plants are often slimy,

374 ECOLOGY

and therefore not readily eaten by such aquatic animals
as snails. The epidermis is usually very thin, and enables
the plants to absorb through it much of their food in the
form of mineral salts and carbon dioxide dissolved in the
water in which they live.

Invasion. Water-plants as land-winners. — Plants growing
in water are not subjected to such extremes as plants
growing in the air, and consequently grow rapidly ; the
rhizomes plough their way through the mud and give off
innumerable shoots into the water. This rapid vegetative
growth enables the plants to spread quickly, and they are
further aided by the ease with which detached shoots grow
and form new plants. On the approach of winter, special
winter buds are formed in many species, such as Pond-weeds
and Frog-bit ; these break off, fall to the bottom, and rest
until the following spring. By such vegetative means,
rather than by seeds (see p. 142), water-plants reproduce
themselves extensively, and rapidly invade the water.

Interesting examples of this may be found in many
ditches, ponds, and lakes. Reed-like plants may be seen
to 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 provides a soil over which the
plants from 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 changes
of conditions which favour a drier type of plant -life, and
it is only a matter of time when it will be succeeded by the
invaders. If further changes should result in improved
drainage, the marsh type will itself be supplanted. In
this 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 of
sand-dunes by grasses and sedges, whose very long rhizomes
bind 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 water-
plants 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, while some, like the
Water Bistort, may be self-pollinated under water, but the
flowers do not open, so that really they are pollinated
in 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
reproduction.

Marsh-plants. — While there is every gradation between
water-plants and marsh-plants, typical examples differ in
several respects. The aerial parts of marsh-plants agree
closely in form and structure with those of land-plants,
and are exposed to similar conditions ; the underground
parts grow in wet, cold, badly-aerated soil. In consequence,
as in aquatics, some marsh-plants have large air-spaces
in their tissues ; others have cylindrical stems and greatly-
reduced leaves, e. g. Rushes and Horsetails. Interesting
modifications, related to differences in transpiration, may
be easily seen in the Meadow-sweet. The lower leaves,
which are exposed to little evaporation, are without hairs ;
the intermediate leaves have patches of hairs on the lower
surface ; and the upper more-exposed leaves have a close
covering of silky hairs, which materially reduce transpiration.

The following is a list of the common plants found
growing 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 these
invaders were : Water Plantain, Common Reed, Bur-reed,
Soft Rush, Marsh Horsetail, Marsh Bedstraw, Bog Stitch-
wort, Ragged Robin, Meadow-sweet, Hairy Willow-herb,
Square-stalked Willow-herb, Lesser Spearwort, Great
Valerian, Large-flowered Bitter-cress, Lady's Smock,
Marsh Marigold, Brooklime, Water Forget-me-not, Marsh
Thistle, Hemp Agrimony, Marsh St. John's-wort, Tufted
Hair-grass. Numerous trees surround the marsh, but only
two of the species have invaded it, the Alder and Willow.
These thrive well in the wet soil, and the marsh is
becoming converted into an Alder- Willow wood.

CHAPTER XXXII

WEEDS

A careful examination of a natural piece of vegetation
produces the impression of a natural blend of colour and
form, 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 suited to the needs or caprice of man.
Even here nature cannot be ignored, and it impresses itself
by topography, soil, and climate in a manner which
compels even cultivation to keep along more or less definite
lines. Nevertheless, man's aim is to substitute for the
less useful native plants those needed by him. In this way
much of the native vegetation is destroyed, but an interest-
ing mesh work persists along the hedgerows (Fig. 244),
roadside patches, and in ditches and streams ; or some

Fig. 244. A Hedgebank with Beaked Parsley,
a common meadow-weed.

376

WEEDS 377

peculiar topographical feature may render cultivation
impracticable, e. g. a steep bank, a moor, copse, or wood,
a mountain or fringe of the shore, and here the native
plants maintain their footing.

(a) Cornfield Weeds

In order to render land suitable for crops, 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 seeds
are sown, and in time germinate. Meanwhile the surface is
exposed to invasion by the native plants which have escaped
destruction. Those with a good dispersal-mechanism, will
stand the best chance of spreading ; others with runners,
such as the Silverweed, or the quick-growing rhizomes of
the Couch-grass, soon make headway. Unless care is taken
to eradicate them they will occupy the soil intended for
the crops, and, being stronger and sturdier, will gain the
mastery. From man's point of view these are ' plants in
the 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 the
same 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
annuals. The ground is prepared for annual crops, and
annual weeds find it a favourable soil, and thrive accord-
ingly; and as long as man disturbs the ground, perennials
have little chance of succeeding. Their opportunity comes
when cultivation ceases ; with a more stable soil, the
sturdy 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
adjacent, more natural areas. Soon the land reverts
practically 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 care-
fully 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, and
on shifting banks ; and some weeds which have somewhat
fleshy leaves may have come originally from such habitats,
e.g. Fumitory (Fumaria officinalis), Hedge Mustard
(Sisymbrium officinale), Charlocks (Brassica Rapa and B.
Sinapistrum) , White Charlock (Raphanus Raphanistrum) ,
Goosefoot (Chenopodium album), Orache (Atriplex patula),
Black Bindweed (Polygonum Convolvulus), Knot-grass
(P. aviculare), Persicaria (P. Persicaria), all of which are
annuals. The Mayweed (Matricaria inodora) is a biennial,
and another frequent weed, the Bladder Campion (Silene
inflata), is a perennial. Other annuals have doubtless
been introduced with impure seed, and those with bright
and showy flowers have probably come from sunnier climes,
e.g. the Poppies (Papaver Rhoeas and P. dubium), Poor
Man's Weather-glass (Anagallis arvensis), and the Corn
Marigold (Chrysanthemum segetum). Many have been
introduced in this way from North and Central Europe and
Asia.

Other common annuals are :

Field Buttercup (Ranunculus arvensis), Red Poppy (Papaver
Rhoeas), Shepherd's Purse (Capsella Bursa-pastoris) , Corn Pansy ( Viola
tricolor), Corn Cockle (Lychnis Githago), Chickweed (Stellaria media),
Spurrey (Spergularia arvensis), Soft-leaved Crane's-bill (Geranium
molle), Cut-leaved Crane's-bill (G. dissectum), Herb Robert (G. Rober-
tianum), Trefoil or Black Medick (Medicago lupulina), Hop Trefoil
(Trifolium procumbens), Tare (Vicia hirsuta), Parsley Piert (Alche-
milla arvensis), Fool's Parsley (A ethusa Cynapium), Cleavers (Galium
Aparine), Field Madder (Sherardia arvensis), Cudweed (Gnaphalium
uliginosum), Groundsel (Senecio vulgaris), Sow-thistle (Sonchus olera-
ceus), Corn Forget-me-not (Myosotis arvensis), Corn Scorpion Grass
(Myosotis versicolor), Ivy-leaved Speedwell (Veronica hederaefolia),

WEEDS 379

Corn Speedwell (V. agrestis), Hemp Nettle (Galeopsis Tetrahit), Red
Deadnettle (Lamium purpureum) and other Labiates, Sun Spurge
(Euphorbia helioscopia) , and Petty Spurge (E. Peplis).

A few are biennials, e. g. :

Spear Thistle (Carduus lanceolatus), Viper's Bugloss (Echium
vulgar e).

Perennial weeds are uncommon in cornfields ; the follow-
ing are examples :

Rest-harrow (Ononis repens), Bush Vetch (Vicia Cracca), Creeping
Cinquefoil (Potentilla reptans), Silverweed (P. Anserina), Willow
Herb (Epilobium montanum), Coltsfoot (Tussilago Far far a), Field
Thistle (Carduus arvensis), Corn Sow-thistle (Sonchus arvensis),
Bindweed (Convolvulus arvensis), Field Mint (Mentha arvensis),
Broad-leaved Plantain (Plantago major), Dock (Rumex obtusifolius) ,
Sheep's Sorrel (Rumex Acetosella), Stinging Nettle (Urtica dioica),
Couch-grass or Wicks (Agropyron repens).

(b) Meadow and Pasture Weeds

Many plants, not usually regarded as weeds, but of little
nutrient value, ma}' occur so abundantly in meadows and
pastures as to reduce considerably the value of the herbage,
and so may be classed as weeds. While annuals are able
to thrive in disturbed and prepared ground, they are ill-
adapted for the struggle with turf -forming perennials, and
so we find that the majority of meadow and pasture weeds
are perennials with effective means of vegetative increase.
Annuals are relatively few, and it is an interesting fact
that among the latter the most persistent are semi -parasites,
living to some extent on the roots of the grasses, e. g.
Yellow Rattle (Rhinanthus Crista-galli) , Eyebright (Euphra-
sia officinalis), Red Eyebright (Bartsia Odontites). Other
common annuals in pastures are the Purging Flax (Linum
catharticum) and Nipplewort (Lapsana communis).

Biennials are few, e. g. Goat's-beard (Tragopogon pra-
tense) and the Soft Brome-grass (Bromus mollis).

38o ECOLOGY

The most abundant weeds of grass-lands are perennials,
namely :

Upright Buttercup (Ranunculus acris), Bulbous Crowfoot (R.
bulbosus), Jack-by-the-Hedge (Sisymbrium Alliaria), Mouse-ear
Chickweed (Cerastium triviale), Rest-harrow (Ononis arvensis),
Meadow Pea (Lathyrus pratensis), Tormentil (Potentilla erecta),
Lady's Mantle (Alchemilla vulgaris), Burnets (Poterium Sanguisorba
and P. officinale), Earth-nut (Conopodium majus), Beaked Parsley
(Anthriscus sylvestris), Wild Carrot (Daucus Carota), Yellow Bed-
straw (Galium verum), Field Scabious (Scabiosa arvensis), Daisy
(Bellis perennis), Yarrow (Achillea Millefolium), Ox-eye Daisy
(Chrysanthemum Leucanthemum) , Ragwort (Senecio Jacobaea),
Knapweed (Centaur ea nigra), Great Knapweed (Centaur ea Scabiosa),
Cat's-ear (Hypochaeris radicata), Autumn Hawk-bit (Leontodon
autumnale), Dandelion (Taraxacum officinale), Cowslip (Primula
veris), Germander Speedwell (Veronica Chamaedrys), Self-Heal
(Prunella vulgaris), Hoary Plantain (Plantago media), Ribwort
Plantain (P. lanceolata), Sorrel or Green Sauce (Rumex Acetosa),
Field Rush (Luzula campestris), Spring Sedge (Car ex caryophyllea),
Yorkshire Fog (Holcus lanatus).

We thus see that for a weed to succeed among the turf-
forming plants of meadows and pastures it must possess
a similar mode of vegetative growth and reproduction, and
be a perennial. Very few annuals succeed here, and of
these the most successful are root-parasites, such as the
Eyebright and Yellow Rattle. But arable land, regularly
disturbed and prepared for the cultivation of annual and
biennial crops, is well adapted to the requirements of annual
weeds.

CHAPTER XXXIII

VEGETATION OF THE SEA-COAST

A glance at a geological map of Britain shows, not only
how 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 381

as clay, sand, and boulders, obscuring the solid rocks be-
neath, so along the coast, thick beds of such materials may
be found, sometimes forming high, easily-denuded cliffs.
Steep rocks offer a jagged resistant line to the tearing action
of the waves, and are covered with spray at every high tide.
At the other extreme, low ground may pass gradually
seawards 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 soil
for 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 still coarser pebbles and boulders
may form banks of shingle. The coast -line thus offers
a great variety of surface and soil, and we might expect
the influence of these variations to be reflected on the coast-
vegetation. But the factor which most powerfully influ-
ences plant-life along the coast is the presence of salt water,
and the plants exposed to its influence show many peculiari-
ties 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 contrast
to the vegetation immediately beyond it. The best -marked
plant-formations of the coast are those of the sand-dunes
and salt-marshes, the vegetation of which impresses us at
once by its peculiar, blue-grey colour.

Seaweeds. — In the sea, or along that part of the coast
often covered by sea-water, seaweeds abound. If the
coast is rocky, brown seaweeds, like the Bladder-wrack and
other species of Fucus and Pelvetia, often form a long belt,
the plants being anchored to the rocks or to stones by
peculiar 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 of much
more lowly organization than the flowering plants, and
differing widely from the latter in not having true roots,
stems, or leaves, and producing no seeds.

Salt-marshes. — Between the tide-marks is a belt destitute
of vegetation ; 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 watch
the constant movement of the surface, we can realize how
difficult it is for plants to secure a root-hold in such unstable
ground. In areas where the ground is bare for longer
intervals, as along the shores of sheltered bays, in estuaries,
or the banks of tidal rivers, land-plants establish themselves,
The muddy soil which accumulates in such localities
provides a peculiar habitat for plants. It is badly aerated,
liable to be covered by sea-water at very high tides, and
there is often much salt in the ground-water. On the other
hand, during exposed intervals, much evaporation may take
place, leading to a concentration of salt in the soil. Or the
reverse is possible ; during heavy rains much salt may be
washed out of the soil. Under such conditions it is not
surprising to find the ground occupied by a peculiar type of
vegetation.

A habitat of this kind is known as a salt-marsh (Fig. 245).
The plants growing here have usually fleshy leaves covered
with a waxy bloom or grey hairs ; some develop short
hairs which break off and form a mealy covering over the
surface. Most salt-marsh plants have a reduced transpiring
surface, and store water in their fleshy tissues. They thus
possess many of the characteristics of xerophytes ; some of
them, however, e. g. the Glassworts (Salicornia spp.) and
Sea Aster (Aster Tripolium) , transpire freely, and are even
able to absorb water by their green surface. Salt-marsh
plants are known as halophytes.

: em r ■ k —

Fig. 245. Salt-marsh on the Banks of
a Tidal River.

Fig. 246. Sand-dunes, their Crests covered with Marram-grass.
382

Fig. 247. Older Sand-dunes. — In the foreground Dwarf Willows ,
in the centre is seen the invasion by Marram-grass.

Fig. 248. Transverse Section of Leaf of Marram-grass.

383

VEGETATION OF THE SEA-COAST 383

The plant best able to withstand salt water is the Glass-
wort (Salicomia), which acts as a pioneer, but near the sea
the plants are few and occur only at wide intervals. The
Grasswrack (Zoster a marina) often occurs in quantity, and
is interesting in that it flowers under water, and has pollen-
grains which float in and are carried by water from the
anthers to the stigmas. Other plants generally met with
on the salt-marsh are the following : Sea Poa (Glyceria
maritima), Sea Arrow-grass (Triglochin maritimum), Sea
Aster (Aster Tripolium), Glasswort (Salicomia radicans),
Sea Oraches (Atriplex spp.), Sea Purslane (A. portulacoides) ,
Sea Spurrey (Spergularia maritima), Sea Lavender (Limo-
nium vulgar e), Sea Plantain (Plantago maritima), Sea Blite
(Suaeda maritima), Scurvy- grass (Cochlearia officinalis) ;
and other species, e. g. Cochlearia anglica, Sea Rush
(Juncus maritimus), Sea Milkwort (Glaux maritima), Buck's-
horn Plantain (Plantago Coronopus), Sea Couch-grass
(Agropyron pungens) .

These species vary much in distribution with the nature
of the ground, as to whether it is muddy or sandy ; low-
lying and wet ; or raised, exposed, and drier. The associa-
tions of plants occurring in these different parts of the salt-
marsh, together constitute the salt-marsh formation.

Rock-plants. — Many of these plants occur also on the
rocks of the coast, especially those washed by the spray.
The more characteristic are : Samphire (Crithmum mari-
timum), Sea Lavender (Limonium vulgar e), Buck's-horn
Plantain (Plantago Coronopus), Sea Pink (Statice maritima),
and Sea Campion (Silene maritima).

Sand-dunes. — If we examine the sand along the shore
which is subjected to the action of the waves, characteristic
ripples will be found on the surface ; but, in addition to
wave-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

little ridges ; the windward slope of each ripple is gradual,
but the lee side is steep (Fig. 246). If we watch the ripples
during high winds we can see them shift their position ; the
sand is blown up the gentler slope to the crest of the ridge,
then rolls down the leeward slope where it is protected
against the wind and is likely to lodge. Thus, while the
windward slope is wearing away, accumulation is going on
on the leeward side. In this way the little ripples move
steadily forwards in the direction in which the wind is
travelling. If in its progress a plant (or even a pebble) is
encountered, a little heap of sand is built up around it, and
it may eventually be buried. If, however, the plant by
continued growth is able to keep its tip above the surface,
the mound may increase in size and form a miniature sand-
dune. It is in this way that sand-dunes are built up, and
they are thus the result of two causes : (1) the action of
wind on mobile sand, and (2) the binding action of plants
which establish themselves on the sand so transported.

The plant which is best able to overcome the difficulties
of shifting sand is the Marram-grass (Psamma arenaria),
which, by virtue of its long perennial rhizomes and deep-
growing fibrous roots, helps to bind the sand together,
while its shoots, by being able to grow and keep above the
surface, not only maintain the existence of the plant, but
aid considerably in building up the dune. By the decay
of the older parts of the plants, humus is added to the soil,
so that the Marram-grass becomes a valuable pioneer of
coast- vegetation. As we have seen (p. 127), the vegetative
mode of reproduction of this plant is put to practical use
along miles of our coasts as a ' land-winner ' (Figs. 247,
80, and 81).

The windward side of a dune is usually bare (Fig. 244),
but on the crest are the Marram-grass and Sea Lyme-grass,
which not only serve as sand-binders but provide protection
and a suitable soil for other species. On the more sheltered

VEGETATION OF THE SEA-COAST 385

leeward side, plants secure a better footing, and more
numerous species are found, which have usually long
rhizomes or deep-growing roots, e. g. Sea Purslane (Arenaria
peploides), Sea Holly (Eryngium maritimum), Ragwort
(Senecio Jacobaea), a variety of the Dandelion {Taraxacum
erythrospermum) , Hawkweed (Hieraceum umbellatum) , Cat's-
ear (Hypochaeris radicata), Sea Bindweed (Calystegia Solda-
nella), Sea Spurge (Euphorbia Par alias), Sea Buckthorn
(Hippophae rhamnoides), Sand-sedge (Car ex arenaria),
Fescue-grasses (Festuca rubra var. arenaria and Festuca uni-
glumis), Sea Couch-grass (Agropyron junceum), and Lichens.
The vegetation of the sand-dune differs in several impor-
tant respects from that of the salt-marsh. The soil-water of
sandy shores does not usually contain much salt, and the
plants growing there, though subjected to the influence of
salt spray from the sea, are not halophytes. The mobility of
the sand, unsuited to most perennials, is the main factor which
determines the character of the vegetation. Our previous
experiments on soils have shown that the capillarity of sand
is less than that of ordinary soil, that water percolates
quickly, and that the water-capacity of the sand is slight.
White sand reflects the heat of the sun, the surface layers
become rapidly heated, water is quickly driven off, and the
air around is hot and dry. At night rapid cooling occurs and
the surface conditions resemble those of a desert. Although
much organic matter may be strewn over the surface, rapid
oxidation takes place, and the sand in consequence is poor
in humus. Rapid percolation of water may also tend to
deplete it, and thus the sand is poor in food-materials.
Further, if a soil which dries rapidly contains 1 per cent,
of salt it may act as a poison to most plants, though they
may be able to withstand two or three times that amount
in a soil which does not rapidly dry. If the surface layer
of sand is removed, the lower layers are found to contain
much moisture even in dry seasons. This moisture is

1296 b b

386 ECOLOGY

probably derived from internal dew in the sand. The
plants able to withstand salting and to endure the severe
conditions along the shore are few in number and for the
most part xerophytes,with tough, leathery, rolled or reduced
leaves (Fig. 248). In some the leaves are fleshy and often
coated with wax, others are spiny, and plants with branch
spines are not uncommon. Grey-green is the prevailing
colour 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 from
the 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 humus ; 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 name
' fixed dune ' is given ; nevertheless, the area is liable to be
covered during high winds by blown sand, and this has an
influence on the character of the vegetation. Cultivated
crops farther inland often suffer materially from the effects
of blown sand. The dominant plants of the fixed dune are :
Sand-sedge {Car ex arenaria), Fescue-grass (Festuca rubra
var. arenaria), and sometimes Sea Couch-grass (Agropyron
junceum). Associated with these and sometimes abundant
are Sea Cat's-tail-grass (Phleum arenarium), Rest-harrow
(Ononis repens), Stork's-bill (Er odium cicutarium), Bird's-
foot Trefoil (Lotus comiculatus) , together with species
occurring on the shifting dunes, and numerous species
which have migrated from adjacent pastures and meadows.
In places, bushes are so abundant as to form thickets, e. g.
Dwarf Willow (Salix repens), Sea Buckthorn (Hippophae

Fig. 249. A Shingle Beach invaded by Orache and Saltwort.

****** 1 m iiilJ^ eW^TT ~*

Fig. 250. Cotton-grass Moor. — Single-headed Cotton-grass in fruit.

387

VEGETATION OF THE SEA-COAST 387

rhamnoides), Burnet Rose (Rosa spinosissima) , Brambles
(Rubus spp.), Honeysuckle (Lonicera Periclymenum), Elder
(Sambucus nigra). Sometimes moorland plants like Ling
(Calluna vulgaris) and Heaths (Erica) occur, and may
eventually invade the ground to such an extent as to give
rise to a typical heath. The association of the shifting
dune thus differs from that of the fixed dune, and within
each association various societies occur. These societies
and associations developed on sand-dunes form the Sand-
dune Formation.

Strand-plants. — Along the strand between the line of
shifting dunes and high-water mark a few plants occur very
sparingly. They are easily overlooked, being almost buried
beneath small dunes an inch or two high. These have all
the characteristics of salt-marsh plants, e. g. Sea Rocket
(Cakile maritima), Sea Kale (Crambe maritima), Sandwort
or Sea Purslane (Arenaria pepioides), several species of
Orache (A triplex), Goosefoot (Chenop odium), Saltwort (Sal-
sola Kali), and Sea Knot-grass (Polygonum Raii). These
form an association of strand-plants.

The strand and a considerable part of the dunes have
a scanty vegetation ; much of the ground is bare, and there
is no competition among the plants. Associations of this
kind are called open associations. On the other hand, in
areas completely covered by vegetation the association is
said to be closed. Examples of closed associations are
pasture, heath, and woodland.

Shingle Beaches

Along many miles of the English coast is a fringe of
shingle, consisting of water-worn stones carried from the
wasting shore, piled up into banks by the alongshore
waves and currents, and driven landward by onshore gales
during high tides (Fig. 249). If the bank is a low one

b b 2

388 ECOLOGY

and covered at high tides by the waves, it is devoid of
vegetation, and, like the sand between tide-marks, the
shingle is moved to and fro freely by the advancing and
retreating tides. On such a shifting surface, plants cannot
grow. Even in larger banks, and when the crest is beyond
the reach of the highest tides, the shingle is more or less
mobile by reason of the heavy impact of the waves and the
readiness with which the sea-water percolates and buoys
up the loose materials of which the bank is composed.

The shingle bank has a steep seaward slope, and a more
gradual landward slope. On the seaward slope very few
plants occur, and the general appearance is that of a bare
bank of rounded stones. The bank is apparently dry, but
if 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 salt. 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 pos-
sible, 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 (Suaeda
fruticosa), Sea Campion (Silene maritima), and the Sea
Purslane (Arenaria peploides). As with sand-binders, the
essential character required is the power of the plant to
grow 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 rolled
over 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 itself. From the prostrate stems,
a tangle of adventitious roots arises, which, together with
the mat of shoots, serves to prevent the removal of shingle
as the water runs down the bank. Further, the shoots
arrest the landward flew of shingle, and the crest becomes
raised beyond the reach of the highest tides ; thus a sea-
wall is 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 {Sedum
acre), Viper's Bugloss (Echium vulgar e), and Sea Pea (Lathy -
rus maritimus) ; or strand-plants, e. g. the Saltwort (Salsola
Kali). Frequently plants from the neighbouring fields and
cultivated ground occur, their seeds having been carried
to the beach by the wind or by birds, e.g. Elder (Sam-
bucus nigra), Woody Nightshade (Solatium Dulcamara var.
marinum), Curled Dock (Rumex crispus), Creeping Butter-
cup (Ranunculus repens), Herb Robert (Geranium Rober-
tianium var. purpureum) . On the more sheltered and stable
landward slope of the beach, plants are more abundant, and
their remains form a humus on which eventually a grassy
carpet may form. In this way the open association of the

390 ECOLOGY

shingle beach may be replaced by a closed association
of pasture species.

The conditions chiefly affecting plant-life on the coast
are mobile soil and salt water. On the disturbed ground
the plants are usually annuals ; anchorage is secured by
deep-growing tap-roots, and the long rhizomes and numerous
adventitious roots of perennials serve as binders for the
loose soil. The shoots are liable to be buried, but their
great power of rejuvenescence enables them to keep above
the surface and aid in building 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 plants
are common, and the epidermis is covered by a grey waxy
bloom or by hairs. In some species the hairs become
detached and form a ' meal ' on the surface. By such
modifications the stomata are protected, transpiration and
radiation reduced, and the water-supply conserved. Plants
possessing these modifications are able to survive the con-
ditions of the habitat, and they give a characteristic
appearance to the vegetation of the coast.

CHAPTER XXXIV

MOORLAND AND ALPINE PLANTS

Many of our English moorlands occupy the sites of former
woodland or scrub, and are extensively developed on the
Pennines and on the Cleveland Hills. Two distinct types
occur : (i) the Cotton-grass moor (Fig. 250) and (2) the
Heather moor (Fig. 251), but these are connected by several
intermediate phases or transition types.

Q
W
H
<!
jz;

O
Q

Ci
O
O

H
W

390

•5 ,*7 ' £jj

«
o
o

a
pq

39i

MOORLAND AND ALPINE 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 is
composed of the remains of previous generations of Cotton-
grass and other moorland plants, and, in places, of Bog-moss
and Hair-moss, while buried at the base of it are numerous
remains of Birch and other trees. Growing on this is a
monotonous stretch, many miles in extent, of closely packed
' tussocks ' or ' hassocks ' of the Cotton-grass ; its growth
being 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 the
Cloudberry, Crowberry (Fig. 253, 1), and Bilberry (Fig. 254,
1). Here and there are patches of Bog-moss, growing over
which are the slender branches of the Cranberry (Fig. 254, 3).
Two species of Cotton-grass are met with. One, by far
the more abundant (Fig. 250), has narrow leaves per-
meated by two rows of large air-channels (Fig. 255, 6), and
when in fruit, bears a single cottony tassel. The other kind,
often confined to wet channels or hollows, has broader leaves
and large air-spaces (Fig. 255, 5), and bears several cottony
tassels on its fruiting shoot (Fig. 158, 1). 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 shallower, the Cotton-grasses
are replaced by Bilberry (Vaccinium Myrtillns), and with it,
but growing less abundantly, are Cowberry (V. Vitis-Idaea),
Crowberry (Empetrum nigrum), and other heath-plants.
Often long Bilberry edges thus arise (Fig. 252). On the
steeper, more sheltered slopes, extensive stretches of

392

ECOLOGY

Fig. 253. Heaths and Heath-like Moorland Plants with
Back-rolled Leaves. — 1, Crowberry; 2, Ling; 3, Cross-leaved
Heath ; 4, Fine-leaved Heath ; a, leafy shoot ; b, transverse
section of leaf ; c, fruiting branch ; d, male flower ; e, female
flower ; /, fruit from below ; g, fruit cut open to show the seeds ;
h, section of leaf of Ling ; *, section of leaf of Cross-leaved Heath.

MOORLAND AND ALPINE PLANTS 393

Bracken are found, and in places wiry rolled-leaved grasses
like the Mat -grass (Figs. 235, 236, 255, 3) and Hair-grass
(Fig. 255, 4) are abundant, and appear as conspicuous
features in the landscape.

Fig. 254. Moorland Plants. — 1, Bilberry ; 2, Cowberry ;
3, Cranberry ; a, leafy shoot ; b, winter shoot ; c, flowering shoot ;
d, vertical section of flower ; e, leafy shoot of Cowberry ; /, under
side of leaf showing pits ; g, section of leaf ; h, section of Cranberry
leaf.

Heather moors. — The above form a transition region to the
Heather moors (Fig. 251). They stand in strong contrast
with the Cotton-grass moors, which are a dull green in early
summer, forming, later on, snowy patches when in fruit, and

394

ECOLOGY

becoming rusty brown in the autumn. The Heather moors
are a lighter green in summer, assuming a rich purple
towards autumn, when the plants are in flower. This is
a region of dwarf evergreen shrubs, the dominant species
being the Ling (Fig. 253, 2).

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-drained siliceous soil ; but
Heather moors also 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. 255. Sections of Up-rolled Leaves of Moorland Grasses
and Sedges.— 1, Tufted Hair-grass; 2, Sheep's Fescue-grass ;
3, Mat-grass ; 4, Waved Hair-grass ; 5, Many-headed Cotton-
grass ; 6, Single-headed Cotton-grass ; a, air-spaces.

together into a compact bed, a few inches in thickness, by
either oxide of iron or humus-compounds. This pan is
often so hard that roots of young trees cannot penetrate it.
The plants found on heaths have many features in com-
mon. The shrubs, with the exception of the Bilberry, are
all evergreen, with greatly reduced, back-rolled leaves, as
shown in Fig. 253. An interesting series comprises Cow-
berry (Fig. 254, 2) with edges slightly curled back, Cranberry
(Fig. 254, 3), and Cross-leaved and Fine-leaved Heaths
{Erica Tetralix and E. cinerea), farther back-rolled (Fig. 253,

MOORLAND AND ALPINE PLANTS 395

3 and 4). In the Crowberry (Fig. 253, 1) the hairy edges
meet, while the Ling has the smallest leaf, and its under
surface is confined to a narrow groove. In all these cases
the stomata occur only on the under surface.

The Bilberry (Fig. 254, 1) usually sheds its leaves in the
autumn, but its bright-green angular stems (Fig. 254, a, b, c)
render it functionally evergreen. Small stunted forms,
however, of the Bilberry retain their leaves through the
winter. The Bilberry is able to withstand great extremes ;
it ascends to a greater altitude than the other species, and
is frequently the dominant plant on high, exposed, rocky
summits.

Moorland grasses have also rolled leaves (Fig. 255).
Along their upper surfaces are ridges, between which are
lines of large, water-containing 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 blade
rolls up. In the grasses, therefore, the blades are up-rolled,
and not, as in the heaths, back-rolled. In the grasses, too,
the stomata 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 either 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 severe
conditions of life on the moors.

The water-logged, acid peat decomposes very slowly, and
the mineral substances it contains are not readily available
for plant-food. Peat-plants, however, agree in one respect
with those growing in humus : they are able to subsist 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 Whin (Figs. 132 and 256), and
it exhibits many interesting modifications which should be

39^

ECOLOGY

carefully studied. What is the nature of the short spines ?
Where and how do they arise ? Distinguish 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, 1). Seedlings may easily be grown,

and the history of the leaves
and spines determined (2 and 3) .
The cotyledons (2, 3, 4, c) are
entire, but the first foliage-
leaves (d) are trifoliate. As the
plant grows, the newer leaves
tend to produce smaller lateral
leaflets, 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-pointed
leaves, and the branches also be-
come sharply pointed, harden,
and so form a branch-spine.
The development of trifoliate
leaves in the seedlings suggests
that the Gorse has probably
descended from an ancestor
with compound leaves, which
now only persist in the seedling
stage. We have already noticed
the interesting way in which
seeds of the Gorse are dispersed by ants (p. 226, Fig. 161).
The Sphagnum bog. — The Sphagnum bog is dominated
by species of Bog-moss (Sphagnum) and other peat-forming
mosses such as the Hair-moss (Polytrichum) . It is de-
veloped on an impervious soil in situations where the air is
very moist, either at low or high levels ; and an essential

Fig. 256. Gorse Seed-
lings.— 1, transverse section
of stems ; 2, young seedling ;
3, older seedling ; 4, different
kinds of leaves on a seedling ;
c, cotyledon ; d to i, transition
from trifoliate leaf to needle-
leaf ; tu, root-tubercles.

MOORLAND AND ALPINE PLANTS 397

condition seems to be a soil poor in lime and other mineral
salts ; it thus differs from a marsh, which is richer in
mineral salts. The Bog-moss grows rapidly; its closely-
packed shoots, and the narrow channels in its leaves, form
a series of capillaries which enable the plant to draw water
up to a considerable height, and hold it firmly. As the
upper branches continue their growth, the lower, older parts
die, and, decaying very slowly, form beds of peat often of
great thickness. If a piece of such peat is examined the
remains of the Bog-moss are clearly seen. On bogs thus
developed are found the Sundews (Fig. 232), Butterwort
(Fig. 234, 1), Cotton-grasses, White Beak- rush (Rhyncho-
spora alba), Purple Moor- grass (Molinia), Bog Asphodel
(Narthecium ossifragum) , Marsh Andromeda (A. Polifolia) ;
and on the drier parts many shrubby heath-plants, e. g.
Cross and Fine-leaved Heaths, Ling, Crowberry (Fig. 253),
Bilberry, Cowberry, Cranberry (Fig. 254), Cloudberry
(Rubus Chamaemorus), also the Sweet Gale or Bog Myrtle
(Myrica Gale) and Creeping Willow (Salix repens).

Alpine Plants

Plants growing on the tops of mountains have many diffi-
culties to contend with. The air is rarefied ; the winds,
often very drying, are at other times moisture-laden ; cold
driving mists alternate with bright sunshine ; hot days are
followed by cold nights ; snow lasts long, especially in the
hollows, and the soil is thin and well drained.

In spite of these varied and fluctuating conditions, many
plants grow here, but they develop dwarfed, tufted, and
other xerophytic growth-forms, well adapted to such a
habitat. Many of the species occur only at great altitudes
and in the Arctic regions. A few are found on the sea-
coast, but they are absent from the intervening lowlands,
e. g. Scurvy-grass (Cochlearia spp.), Sea Campion (Silene
maritima), Sea Plantain (Plantago maritima), and Sea Pink
(Statice maritima). The leaves are often up-rolled as in

398 ECOLOGY

grasses and sedges (Fig. 255), or back-rolled as in heaths
(Fig. 253), with stomata sunk in pits or grooves. The
blades are usually small, leathery, hairy or fleshy, and often
arranged in compact rosettes, forming the cushions so
familiar in rockery plants like the Saxifrages (Fig. 257),
Houseleeks, Cushion Pinks (Silene acaulis), or the woolly
leaves and flowering shoots of Edelweiss (L. alpinum).
Some plants form dense mats of interlacing trailing stems.
Such are the procumbent Azalea, Crowberry (Fig. 253, 1),
Alpine Club Moss (Lycopoditim alpinum), the dwarf forms of
Bilberry, and Alpine Willows. These form a flat carpet
with their numerous rhizomes matted in the soil. Sections
of the Willow-stem may show many (from fifteen to
twenty) annual rings, but in spite of their age the plants
only 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
Pinks, Saxifrages, and Gentians. Vegetative reproduction
by means of offsets, runners, and rhizomes is prevalent.
Viviparous plants (see p. 141) are not uncommon on the
mountains. Examples are Sheep's Fescue (Festuca ovina),
Alpine Poa {Poa alpina), Alpine Bistort, and some sedges.

The study of plants and their distribution reveals the
great power of adaptation which they possess. In relation
to the factors of the environment, plant-organs are modified
in a great variety of ways and present remarkable contrasts
in form and structure, e. g. water-plants and plants of the
sea-coast or the Heather moor ; plants of the moist, shady
woodland and the dry, sunny desert ; trees of the lowland
forest and the flowery cushions of the mountains. Our know-
ledge of the conditions under which these varied forms grow,
leads us to conclude that the main features of the vegetation
of a country are determined by the conditions of the habitat.

The plants of a given association, however, react on the
habitat, and, by changing the conditions of the habitat,
prepare the way for new forms and the extinction of the

g»*W

Fig. 257. A Cushion of Saxifrage.

398

MOORLAND AND ALPINE PLANTS

399

older ones. Such changes may easily be studied in the
vegetation of waste-heaps, quarry-tips, or on the scree-
covered slopes of our mountains. Bare ground becomes
invaded by microscopic plants, Mosses, Ferns, and annual
flowering plants (see p. 220). These are succeeded by open
associations of perennials, which at first are all herbaceous
species, but later, closed associations, with shrubby peren-
nials, are developed, and finally trees appear, with a ground
flora characteristic of the forest.

[FOREST) ;
^ STABLE ASSOCIATIONS

CLOSED
I .
PROGRESSIVE
ASSOCIATIONS

CLOSED
I
RETROGRESSIVE
ASSOCIATIONS

OPEN

invasion <

[bare ground]

Fig. 258. Life-cycle of Vegetation.

The woodland or forest type is the highest and most
stable phase in the development of vegetation, and persists
for a long period. Eventually changes occur, due to natural
or artificial causes, e. g. earth movements, fires, or the
cutting of gaps in the forest for roads or railways. In con-
sequence of the increased exposure, degenerative or retro-
gressive changes set in, and finally the ground becomes
denuded of plants. Re-invasion then occurs, and the life-
cycle of the vegetation is completed by the advent of pro-
gressive associations, which increase in complexity and
stability until the forest is once more developed. In this
way the vegetation of the earth is ever changing.

APPENDIX
EXAMINATION PAPERS

UNIVERSITY OF OXFORD

Local Examinations, July 191 2

Senior

1. Describe concisely the specimen provided. [In describing
an inflorescence or flower, candidates should illustrate the
relative positions of the various parts both by a horizontal
and by a vertical plan.]

2. State briefly how the presence of starch in green leaves
and in underground stems is to be explained.

3. What special structures are found in the wood of a
Dicotyledon ? Explain how the form and nature of these
structures fits them to carry on their special work.

4. Describe the mode of pollination and the relation of
the parts of the flower in two of the following : Willow,
Deadnettle, Evening Primrose, Sunflower.

5. Three leaves of an india-rubber plant are cut off, and
vaseline is rubbed on the under surface of one, on the upper
surface of another, and on both surfaces of a third. They are
then left for a week, hanging in air. State the result in each case.
Give a brief explanation and an account of the physiological
process concerned.

6. Describe briefly the characteristic fruits of Cruciferae,
Scrophulariaceae, and Labiatae. Describe in one case the mode
of seed-dispersal.

7. Give an account of the vegetation to be found in a corn-
field, or a shingle beach, or a sandy heath. Mention six
characteristic plants from the situation you select.

APPENDIX 401

8. Describe three methods of vegetative reproduction
among flowering plants, giving examples of each case. What are
the advantages and disadvantages of this method as compared
with reproduction by seeds ?

9. Give an account of the structure (omitting microscopical
details) and situation on the tree of the male and female cones
of a Pine. How is pollination brought about in the plant ?

UNIVERSITY OF OXFORD
Local Examinations, July 191 i

belonging to the Labiatae.

10. Explain why it is that leaves are usually green, thin,
and flat.

UNIVERSITY OF OXFORD

Local Examinations, July 191 i

Preliminary

1. Describe the flower of either the Buttercup, or the Pea,
or the Wild Rose. State, as far as you can, the uses of the
various parts.

12S6 c c

402 EXAMINATION PAPERS

2. What is the use of the fruit to a plant ? Make drawings
of two fruits which you have examined and name the different
parts.

3. Why does a plant spread its leaves to the light and air ?
Describe two experiments you have seen which prove what
you say.

4. Describe fully how 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 which you have examined.
What becomes of the different parts in spring ?

UNIVERSITY OF CAMBRIDGE

Local Examinations, Dec. 191 i

Senior. A

A 1. Write a concise description of the specimen M [=Bou-
vardia]. Show by means of sketches the relative positions
of the parts of the flower ; and draw attention to any characters
which have special reference to its method of pollination.

A 2 . Describe some simple experiments to illustrate the
effect of light on the growth and development of a green plant.

A 3. What do you understand by vegetative propagation?
Give three examples of structures specially adapted for this
purpose.

A 4. With what habitats would you associate any four of
the following : Gorse, Stone-crop, Dandelion, Whortleberry
(or Bilberry), Sundew, Cleavers (or Goose-grass) ? Mention any
characters of the plants selected which you might regard as
developed in relation to their respective habitats. (Candidates
not in the United Kingdom may, if they wish, substitute the
following question for question A 4 :

Mention three climbing plants, and give some account of
the means by which they gain the required support.)

B 1. Write a botanical account of the specimen N [ = Acacia
seedling]. Explain, so far as you are able, any notable
peculiarities.

APPENDIX 403

B 2. Describe with the aid of sketches the form and arrange-
ment of the parts of the flower of (a) a Buttercup, (6) a Wild Rose,
and point out the chief differences between the two. (Candi-
dates at centres not in the United Kingdom may, if they wish,
substitute the following question for question B 2 :

Describe with the aid of sketches the form and arrangement
of parts of some papilionaceous flower, and suggest the
method by which pollination is effected.)

B 3. Give some account of the phenomenon of leaf -fall and
the changes in the leaf which precede its occurrence.

B 4. Describe the structure of the seed of some monocotyle-
donous plant (e. g. Wheat), and give some account of the
changes which take place in it during germination.

UNIVERSITY OF CAMBRIDGE
Local Examinations, Dec. 191 i

Junior

1. Make labelled diagrams to illustrate the structure of
specimen K [= bud of Brussels Sprouts] and its parts.

2. Dissect specimen L [= fruit of Acer] and describe its
structure by means of labelled drawings. Mention in a few
sentences any points of biological interest which strike you.

3. Why do grasses flourish, although they are closely
cropped by grazing animals ? Explain how it is that grasses
make a firm soft turf and why the grass on a lawn should be
kept short.

4. Give some account of the ways in which plants are
adapted to take full advantage of the light which falls upon
them.

5. Some trees are evergreen, others for part of the year are
leafless. Mention one tree of each kind, and explain as far
as you can the meaning of these different habits.

6. What is a stoma ? In what important functions do
stomata play a part ?

C c 2

404 EXAMINATION PAPERS

7. Name four dehiscent fruits, and describe in each case
how the seeds are enabled to escape.

8. How do water-plants obtain their food ?

UNIVERSITY OF CAMBRIDGE

Local Examinations, Dec. 191 i

Preliminary

1. Describe an experiment which shows that water is given
off from the leaves of a plant during a warm day. From what
source is this water obtained, and how is it carried to the
leaves ?

2. Give two examples of plants which accumulate large
reserves of food at some period of their lives. What is the
advantage of these stores of food to the plants concerned ?

3. What are the chief differences in external features
between roots and stems ? Name a plant which has an
underground stem.

4. Describe briefly the parts of some brightly coloured
flower. Give the name of the flower, and state precisely the
functions of the parts you describe.

5. Describe as fully as you can the appearance presented by
the surface of the stump of a tree after the trunk has been
cut down.

6. The root of a plant grows downwards and the shoot
grows upwards. Explain the importance of these facts in
the life of the plant.

UNIVERSITY OF LONDON

Matriculation Examination, Sept. 191 i

1. Draw a floral diagram and a median, longitudinal
section (on a large scale and showing only the parts cut) of
the flower A provided, naming the different organs. In both
cases the structure of the ovary should be included. Refer
the plant to its natural order, giving your reasons.

APPENDIX 405

2. Make a series of annotated sketches illustrating the
structure of B. Draw from memory a longitudinal section of
the flower from which it has been derived, indicating clearly
the parts which have withered and those which have undergone
further development. All the drawings should be as nearly as
possible on the same scale.

3. Select any five of the following plants and in each case
(a) make descriptive notes of the habitat, (6) state the month
or months of flowering, (c) mention briefly any peculiarities
of habit : Plantain or Waybread (Plantago major), Common
Reed (Phragmites communis), Ling (Calluna vulgaris), Sundew
(Drosera), Marram-grass (Psamma), Thistle (Car dims), Sloe or
Blackthorn (Primus spinosa), Honeysuckle or Woodbine (Loni-
cera Periclymenum) .

4. Make a careful drawing of a portion of a branch of any
plant which climbs by means of tendrils. Indicate the
morphological nature of the tendrils of the plant you select
(giving full reasons for your conclusions) and describe exactly
the way in which they perform their function.

5. Draw three successive stages in the germination of any
seed, showing precisely how the different organs of the embryo
behave. How would you show experimentally what conditions
are necessary for successful germination ?

6. Growing plants are continually absorbing fresh supplies
of inorganic substances from their environment. Describe
in detail how you would find out which chemical elements are
necessary to the life of a green plant. State how and in what
forms the plant obtains each of these elements.

7. Mention four plants that are pollinated by butterflies
or moths and state how their flowers are adapted to these
special insect-visitors. Draw a longitudinal section of the
flower of one of these plants, indicating the positions of the
nectaries, stamens, and pistil, and the position taken up by
the pollinating insect.

8. Enumerate (illustrating the points with the aid of
diagrams) the resemblances and differences of structure
between a Tulip bulb and a Horse- Chestnut bud. What is the
morphological nature of each, and from what sources are the
principal food-supplies obtained when growth recommences ?

4o6 EXAMINATION PAPERS

BOARD OF EDUCATION TEACHERS' PRELIMINARY

CERTIFICATE

Examination, April 191 i

Special Section C. Botany

7. Describe carefully the structure of the flower of the
Orchis, Violet, or Dandelion. Make a drawing of a longitudinal
section of the flower to show clearly the position of the various
parts, and draw the floral diagram.

8. Compare the structure of trie corm of a Crocus with that
of the bulb of a Hyacinth, and show, with the aid of sketches,
how new corms and bulbs are found on the old ones.

9. Draw and describe a leaf of Ivy and compare it with
a leaf of Primrose. Explain any obvious points of structural
difference with reference to the habit of the plant and its
environment.

10. A stone lying in a field is removed and the grass beneath
is found to be discoloured. Account for this, and describe
experiments to show what effect the conditions which produce
discoloration may have upon the growth of the plant.

11. Describe, with the aid of diagrams, the structures
likely to be found upon a branch of Horse- Chestnut in May and
June.

12. What conditions affect the rate of transpiration in
plants ? Describe any experiment which may be made to
determine the rate of transpiration under various conditions,
and sketch the apparatus used.

BOARD OF EDUCATION TEACHERS' PRELIMINARY

CERTIFICATE

Examination, March 191 2

Special Section C. Botany

7. Describe, with the aid of sketches, the two kinds of
flowers which are to be found on Violet plants. What
explanation can be given of the presence of these two kinds
of flowers ?

APPENDIX 407

8. How do plants obtain their food and in what form ?
State clearly the experimental evidence upon which your
statements are based.

9. Give an account of the life-history of the Potato, and show
clearly, with the aid of sketches, on what part of the plant
the tubers are formed. Describe the structure of the Potato
tuber.

10. What experiments could you devise to show how the
rate of transpiration of water from a leafy plant compares
with the rate of absorption of water by its roots ? Upon what
external conditions does the activity of transpiration depend ?

1 1 . Describe some of the common methods by which weeds
are spread. Illustrate your answer by description of three
specific instances of different methods.

12. Describe the structure of the flowers in two plants
which are cross-pollinated by the wind, and in two plants which
are cross-pollinated by insects. State clearly what experi-
mental evidence there is for the statement that, in many cases,
cross-pollination is more effective than self-pollination in the
production of seeds.

BOARD OF EDUCATION TEACHERS' CERTIFICATE

Examination, Nov. 191 1
Special Section C. Botany

7. On cutting across the stem of a plant, such as the Sun-
flower, Begonia, or Pelargonium, it is found, after a short time,
that water exudes from the cut end of that part of the stem
which remains attached to the root. Account so far as you
can for this phenomenon, and describe any experiment which
will throw light upon it.

8. What is meant by ' vegetative reproduction in plants ' ?
Give examples of four different methods of vegetative repro-
duction. Illustrate your answer by sketches.

9. How would you demonstrate the conditions which deter-
mine the formation of starch in leaves ?

10. Give sketches of the leaves of any three of the following :
Gorse, Dog-Rose, Wood Sorrel, Marsh Marigold, Primrose.
Account for any peculiarities of structure observed.

408 EXAMINATION PAPERS

ii. Compare the structure of the seeds of Maize, Wheat,
Oak, and Bean. Show in what respects they resemble or differ
from one another. How would you classify these seeds in
respect of fundamental differences of structure ? Give the
essential characteristics of each class.

12. Mention the names of British plants which possess the
following characteristics, giving an example in each class :

(a) Foliage-leaves in pairs on short special branches.

(b) Reproduction by means of small buds which fall off
and develop into new plants.

(d) Nodules on the roots.

(e) Flowers with stamens and pistil but no calyx or
corolla.

(/) Special adaptations of the leaves to withstand drought.

CENTRAL WELSH BOARD
Annual Examination, July 191 i

Botany

1 . Describe a typical flower. Explain the uses of the various
parts and show how they are adapted to fulfil their functions.

2. What part of a flower is a fruit derived from ? Name
three kinds of dry and three kinds of succulent fruits, and
show in each case how the dispersal of the seeds is brought
about.

3. Describe the vegetation of one of the following localities :
(a) a hedge, (b) a river-side, (c) a wood.

4. What are the distinguishing characters of the order
Rosaceae ? Mention three wild and three cultivated plants
belonging to the order.

5. Give two examples of underground stems. By what
external marks would you distinguish them from roots ?

6. What is meant by respiration ? What parts of plants
respire ? Why should plants not be kept in bedrooms ?

APPENDIX 409

7. Mention four wind-pollinated plants. How would you
recognize a wind-pollinated flower ?

8. Point out the difference between the shoots (i. e. the
stems with their leaves) of a Palm, an Oak, and a Carrot. Of
what advantage is a tall stem to a plant ?

UNIVERSITIES OF MANCHESTER, LIVERPOOL,
LEEDS, AND SHEFFIELD

Matriculation Examination, July 191 i

1 . Describe the structure of a mature sporangium of a Fern,
and explain the functions of its various parts. Why is the
Fern-plant termed the sporophyte ?

2. The embryos of phanerogams have laid up for them,
within the seed-coat, certain stores of organic material to start
them in life ; what is the chemical nature of these reserves,
and in what precise situations are they found ?

3. Give an account of the morphology of any carnivorous
plant with which you are acquainted. Describe the secretory
glands and the nature of the secretion in the type you select.

4. Write a short essay on the dispersal of fruits and seeds
by water, giving illustrative examples.

5. How would you demonstrate practically that plants
respire ?

6. Indicate the distinctive characters of any three of the
following trees : Oak, Elm, Ash, Pine, Willow. Arrange your
answers under the following headings : (a) Mode of growth,
(b) Flowers, (c) Bark.

OXFORD AND CAMBRIDGE SCHOOLS
EXAMINATION BOARD

Higher Certificate

(d) Botany

1. How would you demonstrate by experiment the effect
of the stimulus of gravity on the direction of growth ?

2. Give some account of the process of respiration. What
is its meaning in the life of a plant ?

4io EXAMINATION PAPERS

3. What differences would you expect to find in the seed-
lings of Beans which have been grown respectively under
ordinary conditions and in the dark ?

4. Give some account of the part which is played in plant-
nutrition by (1) sugar, (2) starch.

5. Describe how you would demonstrate experimentally
the growth in length of a root.

6. Give some account of the tissues which are concerned in
the transport of water in a plant.

7. Write botanical descriptions of the specimens A and B;
carefully pointing out in what ways they (1) resemble and
(2) differ from each other.

OXFORD AND CAMBRIDGE SCHOOLS
EXAMINATION BOARD

Higher Certificate

(e) Special Botany

1. Give an account of the tissues which are concerned in
the transport of water through the stemof an ordinary land-
plant.

2. What do you understand by photosynthesis ? Show
how the form and structure of a typical green leaf are specially
adapted to this function.

3. Give three examples of modifications of the shoot for
food-storage. Point out in each case the purpose of the store.

4. Describe with the aid of sketches the spikelet of a species
of grass, and state the function of the various parts which you

describe.

5. Give some account of the methods of seed-dispersal in
the family Rosaceae. State precisely what is the morpho-
logical nature of the various structures to which you refer.

6. Either Give some account of the method of growth and
the life-history (excluding details of fertilization and embryo-
development) of Coltsfoot ; or State what you understand by
the term plant-association, illustrating your answer by one
or more examples.

APPENDIX 411

7. Write a botanical account of the specimen A, and draw
special attention to any structures which bear on its method
of pollination.

' OXFORD AND CAMBRIDGE SCHOOLS
EXAMINATION BOARD

Elementary for Lower Certificates

1. Describe briefly the functions of a foliage-leaf.

2. Draw a diagram of a Potato, naming all the structures
observable. Give your reasons for deciding whether it is
a stem-structure or a root-structure.

3. Explain clearly the difference in origin between the edible
portions of a Cherry and an Apple.

4. Describe, with diagrams, the flower of the Buttercup.

5. Describe, with examples, the various methods of seed-
dispersal with which you are acquainted.

6. Explain why the growth of a plant is checked by trans-
planting it carelessly.

7. Make a careful drawing of the specimen provided, naming
the parts.

COLLEGE OF PRECEPTORS

Certificate Examination, Christmas 191 i
Second Class

1. Describe the specimens before you as fully as possible.
Make diagrams of the floral arrangements (not drawings of the
parts of the flowers). Refer the plants to their classes and
divisions (not orders), giving your reasons.

2. Write down the characteristic features of the orders
Malvaceae and Primulaceae, and show how they differ in the
structure of the pistil.

3. How does the Common differ from the Round-leaved
Mallow, and the Primrose from the Cowslip ? What is the
importance of these differences ?

4. How are the different species of Buttercups adapted to
living in (a) the open meadow {Ranunculus bulbosus), (b) on

4i2 EXAMINATION PAPERS

mud {R. hederaceus), and (c) submerged [R. trichophyllus) ?
State the meaning of the Latin names.

5. What are the functions of ordinary green leaves, and why
have some plants, as the Dodder and Broomrape {Scrophu-
larineae) , no green leaves at all ?

COLLEGE OF PRECEPTORS

Certificate Examination, Christmas 191 i

First Class. Advanced Section

1. Name and describe the flowers of the British genera of
Corylaceae.

2. Explain, with a diagram, the origin of the vascular bundles
of the stipules of the Geranium and Bedstraw.

3. When wild plants are cultivated, what are the most
prominent effects of the change of conditions ? Give examples.

4. Give the life-history of a Moss.

COLLEGE OF PRECEPTORS

Certificate Examination, Christmas 191 i

First Class. Elementary Section

1. Describe the specimens before you as fully as possible.
Make diagrams (i. e. cross-sections) only of the floral arrange-
ments, and refer the plants to their classes and divisions, giving
your reasons for so doing.

2. What genera of Rosaceae are cultivated ? Explain the
changes which cultivation has caused in them.

3. Give examples of roots which have adapted themselves
to other purposes than that of absorbing water from the soil.

4. Describe any experiments in germination. What do they
teach us ?

5. How do plants get rid of superfluous moisture, and why ?

6. Describe the anatomy, as seen in cross-section, of any
ordinary root and the uses of its several tissues.

APPENDIX 413

UNIVERSITY OF BIRMINGHAM
Matriculation Examination, Sept. 191 i

1. Describe the specimen A provided. Refer it to its natural
order, giving your reasons. Illustrate its floral structure by-
horizontal and vertical diagrams.

2. Describe the morphology of the two specimens B and C
provided, and explain any peculiarities of structure they show.

3. Say what you know concerning the formation of starch
by a plant.

4. Give an account of the development of a leguminous
flower from the bud stage to the formation of a seed-pod.

5 . Write an account of the nectaries found in the Ranuncu-
laceae. What is nectar ? Of what use is it to plants ?

6. Describe the movements of organs exhibited by plants
belonging to the Leguminosae and suggest any advantages the
plants may derive from them.

7. Write a description of the various kinds of fruit seen in
the Rosaceae.

8. Describe the seed-leaves of the Castor Oil, Pea, and
Maize, and say how these differ from the leaves subsequently
developed. Why are foliage-leaves and seed-leaves so different?

UNIVERSITY OF WALES
Matriculation Examination, Sept. 191 i

1. Make a large-scale drawing of the flower of A as seen in
median, longitudinal section and name the parts ; draw also
a floral diagram.

2. Describe, with a sketch, the external form of some Fern
with which you are familiar, and compare it in this respect
with such a plant as a Wallflower. Describe the place of
growth of the Fern you select.

3. Describe a simple apparatus to measure the rate of absorp-
tion of water in a cut, transpiring, leafy branch. How would
you (a) increase, (b) decrease the rate of absorption ?

414 EXAMINATION PAPERS

4. Describe the various stages in the opening of the bud of
some tree.

5. What is respiration and what purpose do you suppose it
serves in the life of the plant ? How would you prove that
germinating peas respire ? What do you know of the respira-
tion of green leaves in the light ?

6. What is an insectivorous plant ? Mention three native
insectivorous plants and sketch and describe one of them.

7. Describe and compare, with careful sketches, the pollina-
tion of two flowers, one of which is pollinated by the wind and
the other by insects.

8. What are the advantages and disadvantages of climbing
as compared with the manner of growth of ordinary plants ?

Describe three different ways in which plants may climb.

UNIVERSITY OF DURHAM

Matriculation Examination, Sept. 191 1

1. Write a short account of some one flower which you
have studied, and explain briefly the functions of its various
members.

2. Describe carefully the structure of syncarpous and
apocarpous fruits. Give examples of some common fruits
which come under these heads.

3. Explain clearly how starch is formed in the Potato tuber,
and the source from which this substance is derived.

4. By what experimental evidence can it be shown that
a healthy shoot is continually absorbing water ? How is the
rate of absorption influenced by exposure to light or darkness ?

5. Contrast the external forms of plants grown in darkness,
in shade, and in full illumination.

6. Enumerate and briefly explain the principal means
whereby plants are able to climb, and explain the advantages
which accrue from a climbing habit.

7. Explain clearly the meaning of the knots and lines which
are present in a deal board.

8. Describe as fully as you can the external appearances of
the roots of annual and biennial plants.

APPENDIX 415

UNIVERSITY OF BRISTOL

Matriculation Examination, Sept. 1910

1. Describe fully the specimen A provided and refer it to
its natural order, giving your reasons. Annotated sketches
should accompany your answer.

2. Identify, if possible, and discuss the morphology of the
specimens B, C, and D.

3. Describe as fully as you can the course taken by water
in the plant, from its entrance at the root until its exit from
the leaf. Describe experiments establishing the truth of your
statements.

4. How does the shape of cotyledonary leaves compare with
that of the later leaves of plants ? Can you suggest any reasons
for the differences usually observed ?

5. Describe the pollination-mechanisms known to you as
occurring in the natural order Liliaceae (or Primulaceae).

6. Describe the method of dispersal of seeds exhibited by
the following plants : Rose, Plane, Crane's-bill, Geranium,
Hornbeam, and Campanula.

7. In what manner could you demonstrate the action of
diastase on starch ? What physiological function does this
ferment (or enzyme) perform in the leaves ?

8. Describe the character of the vegetation known to you
as frequenting one of the following situations :

(1) A peaty marsh.

(2) An old overgrown wall.

(3) A sandy sea-shore.

INTERMEDIATE EDUCATION BOARD FOR IRELAND

Examination 191 i (June)

Honours Paper (Third Year)

Section A

1. [Obligatory) Describe the structure of the bulb of some
bulbous plant. What substances does it contain ? Where do
they come from ? What becomes of them ?

416 EXAMINATION PAPERS

2. When do ' evergreens ' shed their leaves ? Compare the
leaves of ' evergreens ' with those of deciduous trees. Can you
suggest any reasons for the difference ?

3. From what sources do the opening buds of spring draw
their supplies of material ? Mention the materials in each case.

4. Describe how the different regions of the root are formed.
What are their uses to the plant ? Give reasons for your answer.

Section B

5. (Obligatory) Of what uses are green leaves to plants ?
Describe experiments and observations which support your
answer.

6. Describe the conditions under which seeds germinate
best. Point out why these conditions are necessary.

7. Describe the appearance of any Fern. Point out some
of the chief differences between a Fern and a flowering plant.

8. What is pollen ? Where is it formed ? What function
does it perform ?

INTERMEDIATE EDUCATION BOARD FOR IRELAND

Examination 191 i (June)

Special Paper (Third Year)

Section A

1. (Obligatory) How do the following insects affect the
growth of plants : Humble-Bee, Aphis (or green fly), grub of
Daddy-long-legs, Wireworm ? State in each case what part
of the plant is acted on by the insect, and whether the result
is beneficial or injurious to the plant.

2. Describe the special characteristics of grasses that inhabit
sand-dunes, and show how these are suitable to the conditions
under which the plants live.

3. How can you tell the age of the branch of a hardwood
tree (e. g. Beech, Lime, Elm) by external and internal features ?
Explain how these features are produced.

APPENDIX 417

4. Give a general account of the autumn tints and the
relative times of leaf-fall of the Oak, Ash, Larch, Beech, and
Horse-Chestnut. Give the order also in which these trees
come into leaf in spring.

Section B

5. (Obligatory) Give an account of the upward and down-
ward flow of sap in a plant. State the source of each and the
general nature of its composition. What is the function of
each kind of sap ?

6. What is meant by the ' sleep ' of plants ? When and
why do they sleep ? Compare the ' waking ' and ' sleeping '
positions of the leaves of the ' Shamrock ' with those of Wood
Sorrel.

7. Describe the inflorescence of the Dandelion, and also one
of its flowers. How is it pollinated, and how is self-pollination
prevented ?

8. Describe the mode of growth and appearance of the com-
mon mushroom or any other fungus of a similar habit. How
does it get a living ? What do you know of ' fairy-rings ' in the
grass ?

INTERMEDIATE EDUCATION BOARD FOR IRELAND

Examination 191 i (June)

Honours Paper (Fourth Year)
Section A

1. (Obligatory) What are the successive steps you would
take in examining the following plants in flower so as to place
them in their orders : Buttercup, Wallflower, Pink, Rose, Pea,
Wild Parsley, Dandelion, Potato, and Stinging Nettle ?

2. Suppose you were to take a class of pupils to a meadow
for a first lesson in the general classification of herbaceous
flowering plants into two great classes, to what features in the
plants would you draw attention ?

1296 D d

418 EXAMINATION PAPERS

3. Describe how tree trunks increase in thickness. As trees
increase in age what changes do the wood and bark undergo ?

4. Give an account of the occurrence of root-nodules on the
roots of some plants. How are these nodules caused, and how
do they affect the life of the plant ?

Section B

5. [Obligatory) Describe an experiment to show that plants
exhibit root-pressure. How is this pressure produced, and of
what advantage is it to the plant ? What natural phenomena
in herbaceous plants are due to root-pressure ?

6. Describe the method of water-culture to prove the
essential inorganic food-materials required by green plants.

7. Draw the vertical section and floral diagram of the Wild
Rose, and name the parts of the section. Draw and describe the
leaf of the Rose.

8. Give examples of varieties, hybrids, and double flowers,
and describe how each may be developed.

INTERMEDIATE EDUCATION BOARD FOR IRELAND

Examination 191 i (June)

Special Paper (Fourth Year)
Section A

1 . (Obligatory) What is respiration ? How may it be shown
that plants respire ? What is the use of respiration ?

2. How would you proceed to find where the most rapid
growth in length of the root and stem takes place ?

3. Describe the changes which take place in the endosperm
of a wheat-grain during germination.

4. Mention some causes of bending and curvature in plants.
How do these causes affect the different parts ? Describe
observations illustrating your answer.

Section B

5. (Obligatory) A square is punched from a Sunflower
leaf before sunrise and carefully weighed. A similar square is
punched from a leaf after sunset, and its weight also recorded.

APPENDIX 419

What difference do you expect to find ? Suggest the causes of
the difference. How would you test your suggestions ?

6. How would you compare the amount of water given off
from the leaves of a branch still attached to a tree, and that
from the leaves of a cut branch supplied with water ? Which
would you expect to transpire the larger amount ? State fully
the reasons on which you base your answer.

7. How is it that young tender seedlings are able to stand up
rigidly ? Why is it that this stiffness disappears when the
seedlings are killed ?

8. What surmises would you form as to the method of
pollination of a flower which has a large white corolla, narrowed
below to a tube, with a honey-gland at its base, and which
emits a perfume towards evening ?

INDEX

The illustrations are indicated in brackets ; the scientific names
of plants are printed in italics.

Absorption by cotyledons, 34.

roots, 33, 48, 54-8.
Acacia, 147, (Fig. 96), 244.

False (Robinia), 150, 151-2.
Acer, 303.

Achene, 212, (Fig. 144).
Achillea, 380.
Aconitum, 236, 237.
Acorn, 212, (Fig. 143).
Actinomorphic, 173.
Adnation, 254.
Adventitious buds, 12 1-2.

roots, 32, 128.

shoots, 60-2.
Aeration of soil, 331, 335.
Aerial roots, 60.
Aesculus, 306.
Aethusa, 247, 378.
Agrimony, Hemp, 376.
Agropyron, 379, 383, 385.
Agrostis, 367.
Air-channels in :

leaf, 100-1, (Fig. 62), 372,
(Fig. 243).

moorland plants, 391, (Fig.

255)-

water-plants, 372.
Ajuga, 254.
Alae, 188, (Fig. 131).
Alder, 236, 286-8, (Fig. 189),
294, 348, 376.

Berry-bearing, 353.
Alchemilla, 244, 378, 380.
Aleurone grains, 23.
Algae, 231, 382.

Blue-green, 220.
Alkanet, Evergreen, 250.
Allium, 266.
Alnus, 286.
Aloe, 266.

Alpine plants, 141, 397-8, (Fig.

257)-
Alstroemeria, 267.
Amaryllidaceae, 266-7.
Amaryllis, 267.
Amphitropous, 208.
Anagattis, 250, 378.
Anatropous, 208.
Anchusa, 250.
Androecium, 16, 158.
Androphore, 241.
Androsace, 250.

Anemone, Wood, 157, 164, (Fig.
no), 192,237,343,350,369.
Anemophilous, 205.
Angiosperms, 232, 264.
Animal-dispersed fruits, 224-6.
Aniseed, 247.

Annual rings, 71, (Fig. 39).
Annuals, 124, 378, 379.
Ant-dispersed seeds, 226.
Anther, 6, 158, 205.
Anthoxanthum, 368.
Anthriscus, 380.
Anthyllis, 368.
Antirrhinum, 256.
Apium, 247.
Apocarpous, 164.
Apple, 119, 171, (Fig. 116), 210,
219, (Fig. 155), 242, 243
(Fig. 166), 244, 358.
Aquatic plants, 343, 370-5.

aeration of, 372.

buds of, 374.

protection of, 373-4.
Aquatic roots, 60, 372.
Aquilegia, 236, 237.
Arabis, 238.
Arachis, 246.
Archangel, Yellow, 254.

422

INDEX

Archichlamydeae, 232, 234, 235,

248, 263.
Arctium, 263.
Arenaria, 385.
Arrowhead (Sagittaria), 371.
Artichoke, Jerusalem (Helianthus

tuberosus), 131, 263.
True (Cynaria Scolymus) , 263.
Arum, 134.
Ash, Common, 23-4, 27, 28, 210,

215, 222, 308-11, 337, 345,

349. 350, 353-
Mountain, 121, 225, 298-301,

348.
Ash woods, 349, 350, 353.
Asparagus, 147, 266.
Aspen, 279.
Asphodel, Bog, 266.
Assimilation of carbon dioxide,

78, 80.
Aster, 263, 382, 383.
Atriplex, 378, 383, 387.
Atropa, 255.
Atropine, 254.
Attitudes of plants, 147-8.
Aubretia, 238.
Autumn Crocus, 157, 266.
Avens, Mountain, 244

Water, 225, (Fig. 160), 244, 349.
Awn, 202, 227, (Fig. 162).
Axillary branches, 12.
Axis, ascending, 12.

descending, 12.

Bacteria, 220, 324.
in root nodules, 326.
in soil, 325-6.
nitro-, 325-6.
Balsam, 74, (Fig. 43), 228, (Fig.

162).
Bamboo, 264.
Banana, 211, 218.

how propagated, 218.
Barberry, 225, 339, (Fig. 219).
Barley, 54, 265.
Bartsia, 256, 379.
Bast, 69, 70.
Beaked Parsley, (see Chervil),

380, (Fig. 244).
Beam, White, 349.
Bean, Broad, 19-23, (Figs. 6, 7),
25, 28, 37 (Fig. 17), 87, 190,
209, 216, 246.

Bedstraw, 348, 361.

Lady's, 369.

Marsh, 376.

Yellow, 370, 380.
Beech, 1 14-18, (Figs. 72, 74-6),
148, 205, 212, 236, 289-91,
(Figs. 190-1), 345> 352,353-
4. 36o.
Beet, 59, 60, 125.
Belladonna, 254.
Bellflower, 155.

Nettle-leaved, 353.
Bellis, 262, 380.
Bent-grass, 367.
Berry, 218-19.
Betony, Wood, 254, 370.
Betula, 236.
Betulaceae, 236.
Bidens, 263.
Biennials, 124-5, 379-
Bifoliar spur, 118.
Bignonia, 222.
Bilberry, 317, 348, 368, (Fig.254).

edge, 391.

moor, 317, 391, (Fig. 252).
Bindweed, 341, 379.

Black, 378.

Sea, 385.
Binomial system, 231.
Birch, 121, 222, 236, 283-6,
(Fig. 188), 294, 345, 348,

352.

Birch wood, 352.

Bird's-foot Trefoil, 386.

Bird's-nest, Yellow, 356, 357.

Bird's-nest Orchid, 356.

Birthwort, 68, (Fig. 36).

Bistort, Water, 375.

Bitter Cress, 348.
Large, 370, 376.

Bittersweet (see Woody Night-
shade), 116.

Blackberry (Bramble), 217, (Fig.
153), 219, 224, 225, 242,
243, 244.

Blackthorn, 119, 225, 339.

Bladder-fern, Brittle, 349.

Bladderwort (Utricularia), 365,
(Fig. 234), 372.

Bladder-wrack, 381.

Bleeding, 98.

Blinks, Water, 343.

Bloom on leaves and fruits, 95-6.

INDEX

423

Bluebell (Wild Hyacinth), 34, 60,
77. 137-40, (Fig. 87), 154,
(Figs. 101, 102), 194, (Fig.
133), 202, 206, 266, 269, 343,

348, 350, (Fig. 225), 369.
Borage, 250.
Boraginaceae, 250.
Borago, 250.

Box leaf, structure of, 65-7,

(Figs. 29, 30).
Bracken, 68, 141, 340, 343, 348,

349. 3 SO, 369.
Bramble, 62, 224, 339, 387.

Stone, 349.
Branch spines, 339 (Fig. 219),

396, (Fig. 256).
Branches, shedding of, 1 18-19,

122.
Branching, 11 9-21.
Brassica, 238, 378.
Broccoli, 238.
Brome-grass, False, 349.

Soft, 379.
Bromus, 379.
Brooklime, 256, 343, 376.
Brookweed, 250.
Broom, 227, 246, 344.
Broomrape(Oo6awcAe), 343, 359,

360.
Brussels Sprout, 103-4, (Fig.

63), 238.
Bryony, Black, 143, (Fig. 90),
144, 225, 341.

White, 144, (Fig. 91), 147, 149,
225, 341.
Buckthorn, 349, 353.
Buckwheat, 56.
Buds, 12, 103-22.

dormant, 12 1-2.

naked, 104, 116.

protection of, 109.

winter, 224, 374.
Bud-scales, 106.

scars of, 1 08-1 8, (Figs. 66, 70,

74, 77)-
Bugle, 254.
Bulbs, 134-40.

descent of, 134, 139.
Bulrush, 222.

Burdock, 226 (Fig. 160), 263.
Burnet, Great, 349, 380.

Lesser or Salad, 244, 368, 370,
380.

Bur-reed, 371, 376.
Butcher's Broom, 266, 354.
Butterbur, 262.

Buttercup, 166-8, (Fig. 112),
174, 192, 204, 206, 212,
(Fig. 144), 233, 237.
Creeping, 389.
Field, 378.

runner of, 67, (Figs. 31, 32).
Tuberous, 166, (Fig. 112).
Upright, 380.
Water, 371, (Fig. 242).
Butterwort (Pinguicula) , 362,
363.

Cabbage, 104, 238.

Cactus, 147-8, (Fig. 96).

Cakile, 387.

Calcareous grass-land, 368.

Callitriche, 343.

Calluna, 317, 387.

Callus, 72-3.

Caltha, 343.

Calystegia, 385.

Calyx, 1 5 .

function of, 15.
Cambium, 35-6, 69.

ring, 36, 70.
Campanula, 155, 216, 223, (Fig.

159), 261, 353-
Campion, 68, 216.

Alpine, 239.

Bladder, 239, 378.

Moss, 239.

Night-flowering, 242.

Red, 204, (Fig. 159), 223, 239,
270.

Sea, 239.
Campylotropous, 208.
Canadian Water-weed (Elodea),

80, (Fig. 50), 223, 372.
Capitulum, 177.
Caprifoliaceae, 258-60.
Capsella, 378.
Capsicum, 255.

Capsule, 216-17, (Figs. 151, 159).
Caraway ' seeds ', 215, 247.
Carbon-assimilation, 84-5.
Carbon dioxide in respiration,

44.
Carduus, 379.
Carex, 380, 385-6.
Carina, 188, (Fig. 131).

424

INDEX

Carmine, 89.
Carnations, 95, 239.
Carnivorous plants, 361.
Carpel, 17, 20, 158.
Carpophore, 215, (Fig. 148).
Carrot, 59, 124, 246, 380.
Carum, 247.

Caryophyllaceae, 239-42.
Castanea, 306.
Castor-oil seed, 210, 226, (Fig.

161).
Catchfly (Silene anglica), 68, 241,

242, 361.
Catkins, 159, 276-94.
Cat's-ear, 380, 385.
Cat's-tail-grass, 386.
Caucalis, 247.
Cauliflower, 238.
Cayenne pepper, 255.
Celandine, Lesser, 60, 62-4, (Fig.

28), 131, 142, 205, 350.
Celery, 246-7.
Cell-wall, 48.
Cellulose, 48.

Censer fruits, 222-3, (Fig. 159).
Centanrea, 262, 380.
Cephalotus, 365.
Cerastium, 339, 380.
Chaerophyllum ( = A nthriscus) ,

247.
Charlock, 124, 378.

White, 378.
Chemical elements necessary for

plants, 55-7.
Chenopodium, 378, 387.
Cherry, 170 (Fig. 115), 171, 217,
(Fig. 152), 224-5.

Bird, 348.

Winter, 210, 254.
Chervil, or Beaked Parsley, 173-
4, (Fig. 119), 193, 204, 215,

247. 343-
Chestnut, Sweet or Edible, 212,

236, 306.
Chick-pea, 147.

Chickweeds, 124, 239, 242,
378.
Mouse-ear, 369, 380.
Water, 239.
Chlorophyll, 67, 84-5.

conditions necessary for

formation, 77-8.
and starch, 80-6.

Chloroplasts (chlorophyll cor-
puscles), 67, (Fig. 29), 85.

Christmas Rose, 237.

Chrysanthemum, 262, 378, 380.

Cicely, Sweet, 247.

Cincinnus, 241.

Cinquefoil, Creeping, 379.

Circinnate, 119.

Class, 231.

Classification of Plants, 229-34.
history of, 229-31.

Claw, 16.

Cleavers, 225, (Fig. 160), 378.

Cleistogamous flowers, 186, 203.

Clematis, 90, 144, (Fig. 92), 164,
(Fig. 109), 168, 222, 237,

34i-

Climbing organs, 143-7, 34°_I-
plants, 143-7. (Figs- 89-94),

340-1 .
Clover, White, 149-50, (Fig. 98),

152, 154, 190, 246, 343, 360,

369-
Club-rush, Marsh, 376.
Cochlearia, 383.
Cock's-foot-grass, 368, 370.
Cohort, 231.

Colchicum, 157, 266, 353.
Cold, effect of, 315, 335-6, 394~S.

397-
Collenchyma, 68.
Colonization, 220.
Coltsfoot, 155, 179-80, (Fig. 123),

214, 222, 262, 379.
Columbine, 155, 186-7, (Fig.

130), 192, 237.
Comfrey, 250.
Companion cells, 69.
Complementary societies, 350-2,

(Figs. 225, 227).
Compositae, 204, 221, 260-3.
Conifers, 270-6, (Figs. 180, 182-4).
Conium, 246.
Connate, 26c.
Conopodium, 247, 380.
Convallaria, 266.
Convolute, 119.
Convolvulus, 379.
Coppice, Ash, 308.
Hazel, 281.
Willow, 277.
Coral-root, 269, 353, 356, (Fig.

228).

INDEX

4-25

Coralorrhiza, 269, 356.

Coriander, 247.

Coriandrum, 247.

Cork, 12, 36, 71-2, (Figs. 15, 38-

40).
Corm of Crocus, 131-4, (Fig- 84).
Corn Cockle, 239, 378.
Cornflower, 226, 263.
Corolla, 16.
Coronilla, 206.
Cortex of root, 34-7, 68.

of stem, 68.
Cotoneaster, 244.

Cotton-grass, 222, (Figs. 158,
250), 39i. 394. (Fig- 255).

397-
-moor, 317, 391.
Cotyledons, absorption by, 34,

134. 274-

Ash, 23-4, 27, 28.

Bean, 21-3, (Fig. 7), 25.

Cress, 26-8, (Fig. n).

Kidney Bean, 26, (Fig. 10), 28.

Maize, 32-4.

Mustard, 25-7, (Fig. 11).

Pea, 23, 27, 28.

Sunflower, 22-3, 27-8, 47, (Fig.
22).

Sycamore, 27, 28.
Couch-grass, 377, 379.

Sea, 385, 386.
Cowslip, 176-7, (Fig. 121), 249,

343. 349» 380.
Cow-wheat, 226, 256, 348, 353,

359.
Crab, Wild, 225.
Crane's-bill, 227, (Fig. 162).

Blood, 349.

Cut-leaved, 378.

Meadow, 204.

Soft-leaved, 378.

Wood, 349.
Crataegus, 244.
Creeping Jenny, 250.
Cremocarp, 215, (Fig. 148), 246.
Cress, Bitter, 348.

Garden, 26, (Fig. 11), 28, 238.

Water, 238, 343.
Crinum, 267.
Crithmum, 247, 383.
Cross-pollination, 164-73.

by insects, 164-200, (Figs.

109-37)-

Cross-pollination by wind, 159-

60, 202, 205, (Figs. 138, 182,

184-9), I91-
Crocus, 60, 1 3 1-4, (Fig. 84).

196-8, (Fig. 135), 231, 267-8.
Autumn (see Meadow Saffron),

157, 266, 353.
Crosswort, 343.
Crowberry, 204-5.
Crowfoot, Bulbous, 380.

Mud, 343.
Cruciferae, 238, 248.
Cuckoo-flower, 348.
Cucumber, 218.
Cudweed, 263, 378.
Cupule, 212, (Fig. 143), 283,

(Fig. 187), 294, (Fig. 194).
Cupuliferae, 236.
Currant, 218.
Black, 353.
Red, 353.
Cuscuta, 361.
Cyclamen, 249.
Cydonia, 244.
Cymes, dichasial, 239.
monochasial, 241.
scorpioid, 250.
Cynara, 263.
Cynoglossum, 250.
Cypripedium, 269.
Cytisus, 246, 301.

Dactylis, 368.

Daffodil, 77, 96, (Fig. 57), 194,
195-6, 198, 202.

Dahlia, 60, 98, 131, 263.

Daisy, 105, (Fig. 64), 153, 177-8,
(Fig. 122), 193, 204, 231,
233, 235, 262, 343, 380.
Ox-eye, 380.

Damson, 217.

Dandelion, 60, 61, 96, 105, 122,
134, 155, (Fig. 104), 180-2,
(Fig. 124), 193, 204, 214,
(Fig. 147), 222, 235, 343,
380, 385.

Date, 218.

Datura, 255.

Daucus, 246, 380.

Deadnettle, 14, 69-70, (Figs.
33-4), 203, (Fig. 172), 263,

343-
Henbit, 252.

426

INDEX

Deadnettle, Red, 254, 379.
White, 254.
Yellow, 348.
Delphinium, 237.
Deschampsia, 367.
Diadelphous, 188.
Dianthus, 239.
Diastase, 86.
Diatoms, 220.
Dichasium, 239.
Dichogamous, 204.
Dichotomy, false, 239.
Diclinous, 204.
Dicotyledons, 24, 194, 230, 232,

233, 234-63.
Diervilla, 258.
Digestion of nitrogenous food,

362-6.
of starch, 85-6.
Digitalis, 256.
Dimorphic flowers, 177, (Fig.

121), 204-5.
Disk florets, 178.
Ditches, plants of, 343.
Dioecious, 160, 204.
Dionaea, 366.

Divi-divi (Caesalpinia), 245.
Dock, 61, 119, 205, 379.

Gurled, 389.
Dodder, 343, 360-1, (Figs. 230-1 .)
Dog Daisy, 262.
Dog's Mercury, 127, 204, 343,

349. 354-
Dogwood, 225, 349, 353.
Dormant buds, 121-2.
Dracaena, 264, 266.
Drip-tip, 341.
Droppers, 137, (Fig. 85).
Dropwort, Water, 247, 343,

370-
Drupe, 217.
Drupels, 217.
Dryas, 244.
Duckweed, 59, (Fig. 26), 60,

372.
Dunes, 383-7.

fixed, 386, 387.

grey, 386.

shifting, 386.

travelling, 386.

white, 386.
Dwarf shoots, 117, 118, (Figs.
74* 77). 271-3, (Fig. 182).

Earth-nut, 247, 380.

Eccremocarpus, 222.

Echium, 250, 379, 389.

Ecology, 315-20.

Edelweiss, 263.

Egg-cell, 207, 209, 210.

Egg-nucleus, 209.

Elder, 14, 71, (Fig. 38), 119, 225,

258, 387, 389.
Elm, 116, 117, 120, (Fig. 27),

122, 148, 215, 222, (Fig.

156), 295-8, (Figs. I95>i97-

8), 337, 36o.
Elodea, 80, (Fig. 50).
Embryo, 21, 23, 24, 30-4, 209-

10.
Embryo-sac, 207, (Fig. 141),

209-10.
Enchanter's Nightshade (Cir-

caea), 354.
Endocarp, 217.
Endodermis, 35, 70, (Fig. 34).
Endosperm, 32, 34, 209-10.
Entomophilous flowers, 205.
Environment, 64.
Eosin, 89.
Ephemerals, 124.
Epicalyx, 168, (Fig. 113).
Epicarp, 217.
Epidermis, 34.
Epigeal, 25-9.
Epigynous, 171.
Epilobium, 343, 379.
Epipactis, 269.
Eranthis, 238.
Erica, 368, 387, 394.
Er odium, 386.
Eryngium, 247, 385.
Essential organs of reproduction,

160.
Etiolation, 77-8.
Euonymus, 353.
Euphorbia, 379, 385.
Euphrasia, 256, 379.
Evening Primrose, 153-4, (Fig.

100).
Exstipulate, 116.
Extrorse dehiscence, 196.
Exudation pressure, 98, (Fig. 60).
Eyebright, 256, 359, 369, 379,

380.
Red, 379.
'Eyes ', 128-9.

INDEX

427

Factors, 317, 335.
climatic, 317.
edaphic, 317.
topographic, 317.
Fagaceae, 236.
Fagus, 236, 289.
False fruits, 219.
Family, 231.

Feather-grass (Stipa), 222.
Fehling's solution test for grape-
sugar, 86, 131.
Fennel, 247.
Ferns, 220, 221, 231.
Bladder, 349.
Lady, 348.
Male, 348, 369.
Marsh, 353.
Fescue-grass, 385, 386.
Meadow, 370.
Sheep's, 367, 368, 370.
Festuca, 367, 385, 386.
Fibrous roots, 59.
Fig, 210, 219.
Figwort, 256.
Filament, 15, 16, 158.
Fir, Scotch {see Pine), 270.

Douglas, 353.
Fixed-light position, 147-8.
Flag, Yellow, 267.
Flax, 361.

New Zealand, 266.
Purging, 369, 379.
Floral diagram, 17.
Flowering Rush, 128, (Fig. 82),

269, 371.
Flowers, 14-18.

biology of, 156-203.
explosive, 191.
irregular, 173
pollination of, 156-203.
structure of, 14-18.
Foeniculum, 247.
Follicle, 216, (Figs. 149, 159).
Forget-me-not, 250-2, (Fig. 170),
263.
Corn, 378.
Water, 376.
Foxglove, 125, 256, (Fig. 174),

343-
Fragaria, 243.
Fraxinus, 308.
Freesia, 267.
Fritillary, 266.

Frog-bit, 60, 372.

Fruits, 17-18, 21 1-19, (Figs. 143-

dispersal of, 219-28, (Figs. 156-

62).
dry, 211-17.
explosive, 215-17, 226-8, (Fig.

162).
structure of, 211-19.
succulent, 217-19, (Figs. 152-
5), 224-5.
Fuchsia, 97-8.
Fucus, 381.
Fumaria, 378.
Fumitory, 378.

Climbing, 341.
Funicle, 19-24, 207-8, (Figs. 6-9,

139. x4i)-
Fungi, 220, 224, 231.

work of, 325, 354, 357.
Funkia, 266.
Furze {see Gorse).

Galanthus, 267.
Galeopsis, 254, 379.
Galium, 378, 380.
Gamopetalous, 175.
Gamosepalous, 172, 174.
Garlic, 141, 266, 343, 348.
Gean, 354.
Genista, 246.
Genus, 11, 231.
Geotropism, 38-9.

negative, 39.

positive, 39.
Geophytes, 140.
Geranium, 378, 389.
Gera,nium{Pelargonium), Garden,
74, 81-3, 172, (Figs. 52,
117).

Field, 172, 174, (Fig. 162).
Germination, 24-34.
Geum, 244.
Gipsy- wort, 254.
Gladdon {see Yellow Flag), 268,

353-
Gladiolus, 134, 267.
Glasswort, 382, 383.
Glaucium, 389.
Glaux, 249, 383.
Gloriosa, 266.
Glumes, 201, (Fig. 138).
Glyceria, 343. 37 1> 383-

428

INDEX

Gnaphalium, 263, 378.
Goat's-beard (Tragopogon), 343,

379-
Gooseberry, 147. (Fig. 95), 218,

(Fig. 154), 225, 339.
Goosefoot, 27^, 387.
Gorse, 190-1, (Figs. 132, 256),

226, 246, 344, 361, 395-6.
Gourd, 218.

Gramineae, 265.

Grape, 86, 211, 218.

Grasses, 142, 200-2, 205, 226,

227, 264-5, 269, 343.
Grass-land, 366-70.

calcareous, 368.

neutral, 368.
Grass-moors, 367-9, (Fig. 235).
Grass-wrack, 375, 3 83 .
Gravity, 28, 38.
Groundnut, 246.
Groundsel, 14, 124, 222, 262,

343. 378.
Growth, conditions necessary for,

34-
of root, 22-5.
of shoot, 25-9, 32-3.
rate of, 77.
Guelder-Rose, 225, 258, (Figs.

175. 219), 340, 353-
Gymnosperms, 232, 233, 276.
Gynobasic, 250.
Gynoecium, 16, 158.

Habenaria, 269.
Hair-grass, tufted, 376.

Waved, 344, 348, 367, 368,

369, (Fig. 255).
Halophytes, 318, 382, 389, (Figs.

2ii, 245).
' Hangers', 353.
Hassocks, 391.
Haustorium, 360, (Fig. 229).
Hawk-bit, Autumnal, 380.
Hawk-moth flowers, 260.
Hawkweeds, 262, 369, 385.
Hawthorn, 62, 116, 121, 225,

244. 337, 339, (Fig. 219),

348.
Hazel, 14, 62, 116, 117, 159,

192, 204, 205, 211-12, 236,

281-3, (Fig. 187), 294, 349,

353, 354-
Heart-wood, 71.

Heath vegetation, 315. (Figs.

251-2), 387.
Heaths, 54, 221, 235, 263, 344,

387, 392, (Fig. 253).
Cross-leaved, 175, (Fig. 120),

193, 368, 394, (Fig. 253).
Fine-leaved, 394, (Fig. 253).
Heather-moor 393-5.
Hedgerows, 224-5, 336-44, (Figs.

218-22).
Helianthcmum, 368.
Helianthus, 262.
Heliotropism, 42, 76-7, (Fig. 46).

negative, 43.
Hellebore, 349.
Helleborine, 269, 349, 353-4.
Helleborus, 236.
Hemlock, 246.
Hemp Nettle, 124, 379.
Henbane, 217, 255.
Heracleum, 247, (Fig. 168).
Herbaceous, 12.
Herb Robert, 343, 378, 389.
Hermaphrodite, 204, 295.
Heteromorphic, 204-5.
Heterophylly, 372, (Fig. 242).
Hibernating organs, 125-42.
Hier actum, 385.
Hilum, 21.

Hip. 212-14, (Fig. 146).
Hippocrepis, 368.
Hippophae, 385-6.
Hogweed, 215, (Fig. 148), 222,

(Fig. 156), 247, 348.
Holcus, 368, 380.
Holly, 225, 339, 348, 350, 354.

Sea, 247, 385.
Honesty (Lunaria), 216, 238.
Honey-dew, 304.
Honey-guides, 185.
Hooked fruits, 225-6, (Fig. 160),

252.
Hop, 361.
Hornbeam, 117, 222, (Fig. 156),

236.
Horse-Chestnut, 108-13, (Figs.

68, 69), 114, 116, 148, 154,

(Fig. 103), 306-8, (Fig.

203).
Horsetail. Smooth (or Water)..

37i, 376.
Marsh, 375, 376.
Hottonia, 249.

INDEX

429

Hound's-tongue, 250.
Humus, composition of, 322.

organisms in, 323-5, 354-5-

plant life in, 354-7.
Hyacinth, Wild, (see Bluebell),

34. 137-
Hyacinthus, 266.
Hydrocharis, 60.
Hydrocotyle, 247.
Hydrophytes, 318.
Hydrotropism, 41-2.
Hygrophytes, 318.
Hyoscyamine, 254.
Hyoscyamus, 255.
Hyphae, fungal, 354-5-
Hypochaeris, 380, 385.
Hypocotyl, 28.
Hypogeal, 25, 28.
Hypogynous, 16, 168, 194.

Indefinite, 164.
Inflorescence, 14-15.
Insectivorous plants, 361-6,

(Figs. 232-4).
Insects, injurious, 163.

as pollinators, 162.

mouth-parts of , 162 (Fig. 108)

useful, 162.
Introrse, 195.

Iodine solution, 22, 23, 31.
Iridaceae, 267-8.
Iris, 128, 198, (Fig. 136), 203,
267-8, (Fig. 178), 370-1.

Yellow, 353.
Invasion, 343-4, 374~5- (Figs.
237-8, 240-1).

quarry tip, 128, 399.

railway bank, 128.

sand-dune, 127-8, (Figs. 80-1),

383-7-
shingle beach, 388-9, (Fig.

249).
water, 374-5- (Flgs- 237-41).
Involucre, 178.
Involute, 1 19.

Ivy, 108, 116, 149, 225, 340,
341-3, (Fig. 222).
Ground, 254.
Ixia, 267.

Jack-by-the-hedge, 343, 380.
John-go-to-bed-at-noon, 153.
Jonquil, 267.

Judas-tree (Cercis), 245.
Juncus, 383.
Juvenile leaves, 29.

Kale, 239.

Keel, 188, 191.

Kidney Bean, 25, (Fig. 10), 28,

245, 246.
Klinostat, 38-9, (Fig. 18), j6,

(Fig. 44). '
Knapweed, 370, 380.
Knotgrass, 378.
Kohl-rabi, 238.
Krakatau, 219.

Labellum, 198, 200.. 268.
Labiateae, 252-4, (Fig. 172).
Laburnum, 49, 121, 246, 301-3,

(Fig. 201).
Lady's Fingers, 368, 370.
Lady's Mantle, 244. 380.
Lady's Smock, 142, 348, 370,

376.
Laminaria, 381.
Lamium, 252-4, 379.
Lapageria, 266.
Lapsana, 379.
Larch (Larix), 222, 231, 233,

274-6, (Fig. 184), 353.
Larkspur, 188, (Fig. 130), 192,

237-
Lathraea, 359-60, (Fig. 229).
Lathyrus, 245-6, 380, 389.
Laurel, 93.

Spurge, 349, 354.
Lavender (Lavendula), 252.
Leaf axil, 12.
Leaf -fall, 72-3, (Figs. 41-2), 108,

113, 122.
Leaves, modified, 29, 147-52,

(Figs. 92-9), 339-42, (Figs.

219-22), 357-66, (Figs. 228-

34), 392-6, (Figs. 253-6).
Leek, 141.

Legume (see Pod), 216.
Leguminosae, 244-6, (Fig. 167).
Lemna, 60, (Fig. 26).
Lemon, 218-19.
Lenticels, 71-2, 281, 283, 286,

292, 299, 304, 311.
Leontodon, 380.
Lettuce, Cos, 104.
Leucojum, 267.

430

INDEX

Leucoplasts, 87.

Lifting power of shoot, 76, (Fig.

45)-
Ligature of stem, 90, (Fig. 54).

Light, effect of, 76-7.

absorbed by chlorophyll, 88.
Ligulate florets, 178, (Figs. 122-

4).
Ligule, 31, 32.
Liguliflorae, 262.
Lilac, 263, 311-H. (Fig. 205).
Liliaceae, 265-6, (Fig. 177).
Lily (Lilium), 134, 266, 269.
Lily-of- the- valley, 127, (Fig. 79),

266, 349.
Limb, 15, 16.
Lime-tree, 122, 148.
Limonium, 383.
Linaria, 256.
Ling, 348, 361, 368, 387.
Linnaea, 260.
Linum, 379.
Lister a, 269.

Lodicules, 202, (Fig. 138).
Lolium, 368.
London Pride, 105.
Lonicera, 258, 260, 387.
Loosestrife, 177, 250.

Purple, 205, 370.
Lotus, 386.

Lousewort, 256, 359, 370.
Love-in-a-mist (Nigella), 238.
Lungwort, 250.
Lupin (Lupinus), 246.
Luzula, 380.
Lychnis, 239, 241, 378.
Lycium, 255.
Lycopus, 254.
Lysimachia, 250.

Madder, Field, 378.

Maize, 30, 33-4, 54, 126, 210,

214, (Figs. 12 and 14).
Mallow, 203, 206.

Round-leaved, 160, (Fig. 107).
Mandrake (Mandragora), 255.
Maple, 215, 222, 353.
Maps of a wood, 347, (Fig. 223).
Marigold, Burr, 225-6, 263.
Corn, 378.

Marsh, 164-6, (Fig. m), 192,
206, 215-16, (Fig. 159), 343,
353. 37«» 376.

Mare's-tail (Hippuris), 371.

Marjoram, 252.

Marram-grass, 127, (Fig. 80),

141, 384, (Figs. 247-8).
Marsh plants, 343, 375-6.
Mat-grass, 367, (Fig. 236), 368.
Matricaria, 378.
Matthiola, 11.
Mayweed, 378.
Mead-grass, 371.

Floating, 343, 371.
Meadow Rue, 237, 368.

Saffron (see Autumn Crocus),

157, 353-
Meadow-sweet, 243, 353.
Meadows, 368-9.
Meal-tree, 116.
Mechanical supporting tissue, 68,

(Figs. 34, 36, 38-40).
Medicago, 222, 378.
Medick, 246, 378.
Megasporangium, 159.
Megaspore, 159.
Megasporophyll, 159.
Melampyrum, 256, 353.
Mentha, 252, 254, 379.
Mericarp, 215, (Fig. 148), 246.
Mesocarp, 217, (Fig. 152).
Mesophytes, 318.
Metachlamydeae, 232, 235, 248-

63.
Micropyle, 21, 25, 207.
Microsporangia, 158.
Microspore, 158.
Microsporophyll, 158.
Midrib, 12.
Milkwort, Sea, 249.
Milfoil, Water (Myriophyllum),

372, 375-
Mimosa, 152, 245.
Mimulus, 256.
Mint, Corn, 254.

Field, 379.

Garden, 252.

Water, 254.
Mistletoe, 116, 358.
Molinia, 368.
Monadelphous, 161.
Monkey- flower, 256.
Monkshood, 187-8, (Fig. 130),

192, 215.
Monocotyledons, 30, 32-4, 70 ,
194-203, 232, 264-Q.

INDEX

431

Monoecious, 160, 204.
Monopodial branching, 119-20.
Monotropa, 356—7.
Moor-grass, Purple, 368.
Moorland plants, 390—7.
Moschatel, 343.
Mosses, 220, 221, 231.
Motile organs, 149.
Mountain Ash, 121.
Movements of flowers and fruits,
152-5.

of plants, 142.

protective, 148, 152.
Mulberry, 210, 219.
Musk, 256.

Mustard, 25, 27, (Fig. 11), 28,
238.

Hedge, 378.
Mycelium, 3 54-5 .
Mycorrhiza, 355-7, (Fig. 229A).
Myosotis, 250, 378.
Myrrhis, 247.
Myrsiphyllum, 147.

Narcissus, 267.

Nardus, 367.

Narthecium, 266.

Nasturtium, Garden, 97, 173,

(Fig. 118).
Nectaries, 160, 198, 206.

extra floral, 206, 258, 340,

(Fig. 219), 365.
on ovaries, 164, 174, 175, 177,

179, 181, 195, 197, 206.
on petals, 166, (Fig. 112), 186,

(Fig. 130), 188, 198, 206.
on receptacle, 169, 170, 171,
172, (Figs. 117, 118), 173,
183, 206.
on sepals, 206.

on stamens, 16, 172, 185, (Fig.
127), 206.
Neottia, 356.
Nepenthes, 365.
Nepeta, 254.
Nettle, Hemp, 254, 379.

Stinging, 68, 343, 353, 361, 379.
Neutral grass-land, 368.
Nicotiana, 254.
Nicotine, 254.
Nigella, 238.

Nightshade, Deadly, 255, 354.
Enchanter's, 225, 354.

Nightshade, Woody, 116, 182-3,
(Fig. 125), 225, 254, 263,

341, 389-
Nipplewort, 379.
Nitrates, 325.
Nitrification, 325-6.
Nitrites, 325.
Nitro-bacteria, 325-6.
Nucellus, 207, (Figs. 140-1).
Nucleus, 48, (Fig. 11), 209, (Fig.

142).
Nutation, 143.
Nutlets, 212, (Figs. 144-7).
Nutrition, 55-8.

in insectivorous plants, 361-6.
in leguminous plants, 245,

326.
in parasites, 358-61.
in saprophytes, 355-7.
Nuts, 211, 212, (Fig. 143), 226,
283, (Fig. 187), 291.

Oak, 14, 116, 122, 159, 192, 204,
205, 236, 291, 294, (Figs.
192-4), 337, 345.

Pedunculate, 291-2, 294.

Sessile, 291-2, 294.
Oak woods, 347-52.

dry, 347-

moist, 348, 349.
Oat, 34, 214, 265.
Obdiplostemonous, 241.
Oenanthe, 247, 343.
Oil stored in seeds, 23.
Oil-bodies on seeds, 226, (Fig.

161).
Onion, 34, 86, 266.
Ononis, 246, 379, 380, 386.
Ophrys, 269.
Orache, 378, 387.
Orange, 211, 218.
Orchidaceae, 268-9.
Orchids, 198, 203, 221, 268-9.
Orchis, Bee, 269.

Bird's-nest, 356-7.

Butterfly, 269.

Early Purple, 198-200, (Fig.
137). 269, 343, 349.

Fly, 269.

Spider, 269.

Spotted, 269.
Order, 231.
Origanum, 252.

432

INDEX

Ornithogalum, 266.

Orthotropous, 208.

Osier Willow, 235, 276-7.

Osmic acid, 23.

Osmometer, Potato, 52-3, (Fig.

24).
Osmosis, 50-4.
Ovary, 17, 159.
Ovule, 17, 159, 206-8.
Oxalis, 1 50-1, (Fig. 99), 205.
Oxygen, necessity for, 43-5, 57.

Pales, 201, (Fig. 138).
Palisade tissue, 66, (Fig. 29).
Palms, 264.
Pansy, 185-6, (Figs. 127-9).

Corn, 186, 204, 206, 378.

Field, 124.
Pap aver, 378.
Papilionaceae, 244-6, (Fig. 167),

248.
Pappus, 180.
Parachute fruits, 221-2.
Parasites, 343, 358-61, (Figs.

229-31).
Paris, Herb, 266, 353.
Parsley, 247.

Beaked (see Chervil), 173, 380.

Fool's, 247, 378.

Hedge, 247.

Piert, 378.
Parsnip, 246.
Passion-flower, 144, 147, (Fig.

93).

Pastures, 366-9.

survey of, 369.
Pea, Edible or Garden, 21, 23,
27, 28, 87, 116, 190, 210,
216, 246.

Meadow, 380.
Peanut, 246.

Pear, 119, 171, 210, 219, 244.
Pearl wort, 239.

Peat, 3I5-J7. (pig- 209), 391-5.
Pedicel, 15.
Pedicularis, 256.
Pelargonium, 74, 81, 82, 172.
Pelvetia, 381.

Pennywort [Cotyledon), 344, (Fig.
221).

Marsh, 247.
Pentamerous, 241.
Pentstemon, 256.

Pepper, 210.
Peppermint, 252.
Perennation, 125.
Perennials, 125, 379, 380.
Perfoliate, 260.
Perianth, 194.
Pericarp, 18, 31.
Perigynous, 169, 170.
Perisperm, 210.
Persicaria, 378.
Petaloid, 164.
Petals, 16.
Petasites, 262.
Petioles, 12.

mechanical structure of, 68.
modified, 147, (Figs. 92-6),

152.
Petunia, 254.
Peucedanum, 246.
Phaseolus, 246.
Phleum, 386.
Phloem, 69.
Phormium, 266.
Photosynthesis, 79-80.
Phragmites, 371.
Phylloclade (or cladode), 147,

(Fig. 96), 266, 372.
Phyllode, 147, (Fig. 96), 366.
Phyllotaxy, 14.
Physalis, 210, 254.
Pimpernel, Bog, 250.

Scarlet, 204, 216, (Fig. 151),

250.
Pimpinella, 247.
Pine-apple, 210, 219.
Pine, Scots, (Fig. 67), 1 18-19, 204,

205, 222/(Fig. 156), 231,

233, 270-4, (Figs. 182-3),

345. 347. 348. 352.
Pmks, 95, 239, 241.
Pinus, 270.
Pistil, 16, 17, 31, 158-9, 206-7,

(Fig. 139).
Pisum, 246.
Pitcher-plants, 365-6.
Pith, starch stored in, 91.

use of, 97.
Placenta, 17, 19, 20, 206.
Plane-tree, 304.
Plant-associations, 233-4, 319-

20, 345-99-
closed, 387, 399.
open, 387, 399.

INDEX

433

Plant-associations, progressive,

399-

retrogressive, 399.
Plant-communities, 319, 320.
Plant-formations, 319.
Plant-societies, 233, 319, 352.
Plantago, 379, 380, 383.
Plantain, 105, 204, 205, 217.

Broad-leaved, 379.

Buck's-horn, 383.

Hoary, 368, 370, 383.

Narrow-leaved or Ribwort,

369, 380-

Water, 269, 371, 376.
Plasmatic membrane, 5 1 .
PI at anus, 304.
Plum, 119, 170, 217, 243, (Fig.

166).
Plumule, 21, 23, 24, 28.
Poa, Reed, 371.
Pod of Bean, 19-20, (Fig. 6),

216.
Pollard trees, 235, 277.
Pollen-flowers, 164, 170.
Pollen-grains, 16, 158, 162.

germination of, 208-9, (Fig.
142).
Pollen-sacs, 16, 158.
Pollen-tubes, 208-9.
Pollination, 159, 203-6.

cross-, 160-1, 164, 204.

insect-, 161, 205.

self-, 160-1, 164, 177, 179, 181,
186.

wind-, 159-60, 202, 205.
Pollinia, 199.
Polygonatum, 266.
Polygonum, 378, 387.
Polypetalous, 16, 174.
Polypody, 344.
Polysepalous, 15.
Pome, 219.
Pomegranate, 219.
Ponds, vegetation of, 371-5,

(Fig. 239).
Pond-weed, 223, 269, 371, 375.
Poor Man's Weather-glass {see
Scarlet Pimpernel), 153,378,

379-
Poplar, 62, 116, 119, 160, 204,
205, 279, (Fig. 186), 294,
358.
Aspen, 279.

1296 E e

Poplar, Balsam, 279.
Black, 279.
Lombardy, 279.
White, 279.
Poppy, 155, 216, (Fig. 151), 223,
378.
Horned, 389.
Populus, 279.
Potamogeton, 269.
Potato, 128-9, (Fig- 83), 182,

254.
Potentilla, 379, 380.
Poterium, 244, 368, 380.
Potometer, 93 (Fig. 56).
Prefoliation, 119.
Prickles, (Fig. 114), 339.
Primrose, 105, 176-7, (Fig. 121),
193, 205, 231, 233, 235, 249,
(Fig. 169), 263, 343, 350.
Evening, opening flowers of,
154, (Fig. 100).
Primula, 249, 380.
Primulaceae, 248-50.
Privet, 107-8, (Fig. 65), 149.313,

314, (Fig. 205), 349, 353.
Protection :

of bud, 158, 196.
of chlorophyll, 147-8.
of honey, 155, 171, 173, 176,
183, 186, 188, 197, 198, 313.
of leaves, 67, 106, 155, 344,
382, 384, (Fig. 248), 386,
390.
of plumule, 25, 33,
of pollen, 155.
of stem, 72, 390.
of stomata, 95.
Protective movements, 148-

55-
Proteins, 246.
Proterandrous, 172, 204.
Proterogynous, 171, 204.
Protoplasm, 27, 48, 209.
Prunella, 380.
Prunus, 354.

Psamma (=Ammophila), 384.
Pseudocarp, 219.
Pteris, 343.
Ptyalin, 86.
Pulmonaria, 250.
Pulses, 246.
Pyrola, 353.
Pyrus, 244, 298.

434

INDEX

Quercus, 236, 291-4, (Figs. 192-

4).
Quicken-tree, 298.
Quick-grass, 125, 140.
Quince, 244.

Raceme, 15, 194, (Fig. 133).
Radicle, 20, 21, 22, 23.

pocket, 20-1.
Radicula.. 343.

Radish, 35, 59, (Fig. 26), 125,
238.

Horse, 238.
Ragged Robin, 239, 370, 376.
Ragwort, 262-3, 370, 380.
Ranunculaceae, 236, 242, 248.
Ranunculus, 236-7, 343, 378, 380.
Raphanus, 378.
Raspberry, 62, (Fig. 27), 122,

217, 225, 242-3.
Ray-florets, 178-80.
Receptacle, 15, 16.

-cup, 170, 171.
Reed, Common, 371, (Fig. 240),

376.
Region of elongation :

in roots, 45, 46, (Fig. 21).

in shoots, 47 (Fig. 22).
Replum, 17.
Reproduction, vegetative, 140-2.

in aquatic plants, 374.
Reproductive organs, 14-18,

206-1 1 .
Respiration, 43, 44, 107.
Rest-harrow, 246, 379, 380, 386.
Revolute, 119.
Rhinanthus, 256, 379.
Rhizomes, 125-8, (Figs. 79-81

and no).
Rhododendron, 89, 93, 119.
Ribwort {see Plantain), 105, 106.
Rice, 265.
Roan-tree, 298.
Rock-plants, 383.
Rock Rose, 368.
Root, 12.

abnormal, 59-60, (Fig. 26).

absorption by, 48, 57.

aerial, 60.

aquatic, 60.

bast (phloem) of, 35.

-branches, 12.

cambium of, 35.

Root-cap, 12, 58.

contact stimulus, 40.

contractile, 134, (Fig. 84),
139. (Fig. 87).

cortex of, 34.

curvature of, 46, 47.

dicotyledonous, 34-6.

direction of growth, ^, 38.

effect of dry and moist soils
on, 42.

effect of light on, 42-3.

endodermis of, 35.

environment of, 64.

epidermis of, 34.

excretion by, 49.

forms of, 58-64.

geotropism, 38-40.

growing region of, 45-6.

-hair region, 48.

-hairs, 12, 27, 48, 62.

hydrotropism, 41-2.

monocotyledonous, 32, 36-7.

-nodules, 245, 326, 356.

old, 34.

oxygen necessary for, 43, 44.

pericycle of, 35.

-pressure, 97-8, (Fig. 60).

secondary growth, 35, 36.

sensitiveness of, 38-47.

sensory region of, 40, 41.

separation layer, 139.

stele or central cylinder, 35.

storage of food by, 59, 60.

structure of, 34-7.

-system, 12.

tap, 12, 58, 59.

tissues, 34-7.

tuberous, 60, 62, (Fig. 28).

vascular system of, 35.

wood (xylem) of, 35.

work of, 37-58.

young, 35, 36.
Rosa, 244, 387.
Rosaceae, 242-4.
Rose, 62,90, 116, 122, 170, (Fig.
114), 171, 174, 193, 210,
212-14, (Fig. 146), 219, 225,
244.

Burnet, 387.
Rosemary, 252.

Rosette plants, 105, 106, (Fig.
59), 250, 344, 398, (Fig. 257).
Rosmarinus, 252.

INDEX

435

Rostellum, 199, 200.

Rowan (see Mountain Ash),

244, 298-301, (Figs. 199,

200).
Rubus, 243, 387.
Rumex, 379, 380.
Ruscus, 266.
Rush, Soft, 376.

Field, 369, 380.
Rushes, 226, 348, 370, 375.
Rye, 265.
Rye-grass, 368.

Saccate, 16.

Saffron, Meadow (see Autumn

Crocus), 353.
Sage, Garden, 252.

Wood, 254.
Sagina, 239.

Sainfoin (Onobrychis) , 246.
St. John's-wort, Marsh, 376.
Salicaceae, 235-6.
Salicornia, 382—3.
Salix, 235, 386.
Sallow (see Willow), 235.
Salsola, 387, 389.
Salt in soil, 382, 385.
Salt-marsh, 319, 382-3, (Figs.
211, 245).

formation, 319, 383.

plants, 382-3.
Saltwort, 387-9.
Samara, 215.
Sambucus, 258, 387, 389.
Samolus, 249.
Samphire, 247, 383.
Sand-dune (see Dune), 318, 319,

(Figs. 210, 246-7), 383-7-
Sand-sedge, 127, (Fig. 81), 385,

386.
Sandwort, 239, 387.
Sanicle, Wood, 225, 248, 348,

354-
Sanicula, 248.
Sap, 48, 89, 90, 98.

ascent of, 89, 90, 98.

descent of, 90.
Saprophytes, 355-7, (Fig. 228).
Sap-wood, 71.
Sarracenia, 365.
Saxifrage (Saxifraga), q8, (Fig.

59). IOS. 344-
Scabiosa, 368, 380.

Scabious, 261, 368.

Field, 380.

Small, 349, 368, 370.
Scarlet-Runner, 25, (Fig. 10),

188, 190, 245, 246.
Scent of flowers, 18.
Scilla, 266.

Sclerenchyma, 68, (Fig. 36).
Scorpioid cyme, 250.
Scorpion-grass, 378.
Scots' Pine (see Pine), 1 18-19.
Scrophnlaria, 256.
Scrophulariaceae, 255.
Scutellaria, 254.
Scutellum, 31-3, (Figs. 13-14).
Sea Arrow-grass, 383.

Aster, 382, 383.

Bindweed, 385.

Blite, 383, 388, 389.

Buckthorn, 385, 386.

Campion, 239, 383, 388, 389.

Cat's-tail, 386.

Couch-grass, 383, 385, 386.

Holly, 385.

Kale, 387.

Knotgrass, 387.

Lavender, 383.

Lyme-grass, 384.

Milkwort, 383.

Orache, 383.

Pea, 389.

Pearlwort, 239.

Pink, 383.

Plantain, 383.

Poa, 383.

Purslane, 239, 383, 385, 387,
388, 389.

Rocket, 387.

Rush, 383.

Spurge, 385.

Spurry, 239, 383.
Sea-coast, vegetation of, 380-90.
Seaweeds, 381-2.
Secondary growth, 35, 36, (Figs

15. 16).
Sedge, 142, 205, 226.

Sand, 127, (Fig. 81), 385, 386.

Spring, 380.
Sedum, 389.

Seed dispersal, 221, 222-4, 226-8.
Seeds of Dicotyledons, 19, 30.

of Monocotyledons, 30-4.
Selaginella, 222.

436

INDEX

Self-heal, 254, 380.
Semi-parasites, 256, 358-9.
Senecio, 262, 378, 380, 385.
Sensitive-plant, 152, 245.
Sepals, 15.

Separation-layer, 72-3, (Figs. 41,
42).

inleaves, 73, 108, (Fig. 65), 122,
310.

in roots, 139, (Fig. 87).

in shoots, 122.
Sesleria, Blue, 370.
Shade, effect of, on growth,

348.
Shade plants, 348.
Shade position, 147-8, (Fig. 95).
Shepherd's Purse, 124, 215, (Fig.

ISO). 238, 378-
Sherardia, 378.
Shingle beaches, 387-90, (Fig.

249).
Shingle-binding plants, 388-9.
Shoots :

adventitious, 60-2, (Fig. 27),

122.
ascent and descent in the soil,

128, (Fig. 82), 134, 137,

139-

deciduous, 122.

dwarf, 117, 118, 121, (Fig. 74).

effect of stimuli on, 74-7.

elongated, 121.

environment of, 64, 65, 123-4.

growing region, 47, (Fig. 22).

growth of, 25-30.

modified, 123-42.

rate of growth of, 77-8.

scars, 113, (Fig. 68).

sensitiveness of, 74-7.

shedding of, 122.

stool-, 1 21-2.

underground, 125-40.

work of, 74-103.
Side-saddle Flowers, 365.
Sieve-tubes, 69, (Fig. 32).
Silene, 239, 241, 242, 361, 378,

383, 388.
Silverweed, 141, 242, 7,77. 379-
Sisymbrium, 378, 380.
Skeleton of leaf, 65, (Fig. 30J.

of stem, 70, (Fig. 33).
Skullcap, Greater, 254.
Sleep-movements, 149-52.

Smilax, 147, (Fig. 96), 266.
Snapdragon, 125, (Fig. 159), 256,

(Fig. 174).
Snowberry, 258.
Snowdrop, 136.
Snowflake, 267.
Social plants, 142.
Soft-grass, 125, 343, 348, 350.
Soils, 320-36.

aeration of, 331, 335, 372-3,

375-

calcareous, 331.

capillarity of, 332-3.

composition of, 321.

effect of hoeing, 334-5.

humus-content, 322.

liming, 332.

organic matter in, 322.

organisms in, 54-5, 323-6.

permeability of, 330.

physiologically dry, 336.

properties of, 328-31.

salts in, 382, 385.

sedentary, 320, (Fig. 212).

transported, 321, (Fig. 213).

water-content, 322.

water-supply, 335-6.
Solanaceae, 254-5.
Solarium, 254-5.
Solomon's Seal, 128, 266, 349.
Sonchus, 378, 379.
Sorrel or Green-sauce, 380.

sheep's, 369, 379.
Spathe, 196, (Fig. 134), 198, (Fig.

136).
Spearwort, Lesser, 343, 370, 376.
Species, 11, 231.
Speedwell, Corn, 379.

Germander, 183-5, (Fig- I26),
193, 256, 263, 369, 380.

Ivy-leaved, 378.

Marsh, 256.

Water, 256.
Spergula, 239.
Spergularia, 239, 378, 383.
Spermaphyta, 231, 233.
Sphagnum bog, 396-7.
Spindle Tree (Euonymus), 225,

349. 353-
Spines, branch, 339.

leaf, 339.

Spiraea, 243.

Spiranthes, 269.

INDEX

437

Spleenwort, Black (Asplen um),

344-
Spongy tissue, 66, (Fig. 29).
Spores, 158, 221.
Sporophyll, 158.
Spruce, 353.
Spur, bifoliar, 118.
Spurge, Petty, 379.

Sea, 385.

Sun, 379.
Spurry, Corn, 239, 378.

Sea, 239.
Squill, 136.
Stamen, 16, 158.
Stamen-trough, 188.
Staminode, 186, 199, 200.
Standard, 188, (Fig. 131).
Star of Bethlehem, 266.
Starch, conditions necessary for
formation of, 80-5.

conversion into sugar, 86.

formed from sugar, 87.

digestion of, 85—6.

potato-, 87 (Fig. 53).
Starch-print, 81 (Fig. 51).
Starwort, 343.

Bog, 370.
Statice, 383.
Stellaria, 239, 343, 378.
Stem, 12.

annual rings in, 71, (Fig. 39).

bast of, 69.

cambium of, 69.

cortex of, 68.

curvature of, 74-7.

cuticle of, 67.

effect of gravity on, 74, (Figs.

43-4)-

ligature on, 90, (Fig. 54).

light on, 76-7.
endodermis of, 70, (Fig. 34).
epidermis of, 67-8.
force of growing, 76.
growing region of, 47, (Fig.

22).
path of sap in, 89, 90.
pith of, 69.

secondary growth, 70-1.
structure of, 67-7 1 .
supporting tissues of, 68.
underground, 125-40.
vascular bundles of, 68-71,
(Figs. 31-9).

Stem, wood of, 69-70.

woody, 70-1, (Figs. 38, 39).
Stigma, 17, (Fig. 3), 159.
Stimulus, effect of, on root, 38-

43-
on shoot, 74-7.
Stipulate leaves, 116.
Stipules, 29, 1 16.

as bud-scales, 116.
Stitchwort, 239-42.

Bog, 239, 343, 370, 376.
Marsh, 348.
Stock, Garden, 11-18, (Figs. 1-4),
171, 174,192,204,206, 210,
216, 231-3, 238.
Stomata, 66, 67, (Fig. 29).
opening and closing of, 98.
protection of, 95-6.
sunken, 398.
water, 98.
Stonecrop, 344.

Biting, 389.
Stoneworts (Chara), 372.
Stool-shoots, 1 2 1-2.
Stork' s-bill (see Crane's-bill), 386.
Strand-plants, 387.
Strawberry, 141, (Fig. 88), 168,
(Fig. 113), 171, 174, 193,
210, 212, (Fig. 145), 219,
225, 242-4, 354.
Style, 17, 159.
Suaeda, 383, 388.
Succulent fruits, 217-19 (Figs.

152-5)-
Succulent or fleshy plants, 344,

398.
Suckers, 60-2, (Fig. 27), 280,281.
of parasites, 358, 361, (Figs.

229-31).
Sucking-organ, 139.
Sugar, conversion into starch,

84, 85.
grape, 85, 86, 131.
Sundew, 362, (Figs. 232, 233), 397.
Sunflower, 23, (Fig. 8), 27, 28,

47, (Fig. 22), 68, (Fig. 37),

98, 262.
Sun-position, 147-8, (Figs. 95,

96).
Survey of a pasture, 369.

of a wood, 346-9, (Fig. 223).
Swede, 238.
Sweet Gale, 353, 397.

438

INDEX

Sweet-Pea, 29-30, 144, 147, 188-
90, (Fig. 131), 227, (Fig.
162), 235, 246.

Sycamore, 11 2-14, (Figs. 70-1,
73), 117, 120, 122, 149, 214-
15, 222, 303-6, (Fig. 202),

337-
Symbiosis, 355-6.
Sympetalae, 232, 248.
Symphoricarpus, 258.
Symphytum, 250.
Sympodial branching, 1 19-21.
Syncarpous, 17, 171.
Syngenesious, 178, 261.
Syringa, 311.
Systematic botany, 229-33.

Tap roots, 12, 58, (Fig. 26).
Taraxacum, 380, 385.
Tare, 246, 378.
Tea-tree, 255.
Teasel, 261.
Temperature, effect on

absorption, 123, 336.

carbon-assimilation, 84.

distribution, 315-17, 395, 397.

germination, 34.

transpiration, 95.
Tendrils, 30, 144-7, (Figs. 91-4,

131), 341, (Fig. 220).
Testa or seed-coat, 21, 23, 24, 28,

3i-
Teucrium, 254.
Thalictrum, 237.

Thistle, 214, 222, 262, 343, 348,
361.

Field, 379.

Marsh, 376.

Sow, 378, 379.

Spear, 379.
Thorn-apple, 255.
Thyme, Wild, 252, 361, 370.
Thymus, 252.
Toadflax, Yellow, 256.

Ivy-leaved, 256, 344.
Toadstool, Sulphur-tuft, 355,

(Fig. 226).
Tobacco, 254.
Tomato, 218, 255.
Toothwort, 343, 359, (Fig. 229),

360.
Tormentil, 243,244, 348, 369, 380.
Tragopogon, 379.

Transpiration, 91-5.

amount of, 92, (Fig. 55).
circumstances favouring, 95.
force of, 98.
rate of, 94, (Fig. 56).
reduction of, 95, 382, 386, 390,

395-
suction action of, 99, (Fig. 61).
Traveller's Joy {see Clematis),

164, (Fig. 109), 353.
Trees, 106-22, (Figs. 65-78),

270-314, (Figs. 180-205).
Trefoil, Hop, 378.
Trientalis, 250, 353.
Trifolium> 246, 378.
Triglochin, 383.
Trimorphic flowers, 177, 205.
Tritoma, 267.
Tropophytes, 318.
Tubers, root-, 60, 62-4, (Fig. 28).

stem-, 128-31, (Fig. 83).
Tubular flowers, 171—92, (Figs.

1 1 5-1 8, 120-30).
Tubuliflorae, 262.
Tulip, 134-7, (Figs. 85-6), 207,

266.
Tulipa, 266.
Tunicated bulb, 135.
Tunics, 135.

Turgidity, 52, 96-7, (Fig. 57).
Turnip, 59, (Fig. 26), 125, 238.
Tussilago, 379.
Tussocks, formation of, 367, (Fig

236).
Tway-blade, 269, 349.
Twining stems, 142-4, 341.
clockwise, 144, (Fig. 90), 341.
contra-clockwise, 144, (Fig.

89), 34i-

Ulex, 246.

Ulmus, 295.

Umbelliferae, 246-8, (Fig. 168).

Umbels, 173, 246.

compound, 173.

simple, 176, (Fig. 121).
Urtica, 379.

Valerian, 222, ij6.
V actinium, 317, 391.
Vascular bundles, 68-71, (Figs.
3i-4o).
closed and open, 70.

INDEX

439

Vegetable Marrow, 28.
Vegetation, study of, 315-20,

(Figs. 163, 206, 208-11).
grass-lands, 366-70, (Figs. 235-

6).
hedgerows, 336-44, (Figs. 218-

22, 244).
meadows, 368-9, (Fig. 163).
moors, 390-7, (Figs. 250-6).
mountains, 397-8, (Figs. 163,

206, 257).
pastures, 366-70.
ponds, 370-5. (Figs. 238-43).
salt-marshes, 382-3, (Figs.

211, 245).
sand-dunes, 383-7, (Figs. 80-

1, 210, 246-8).
sea-coast, 380-90, (Figs. 210,

211, 245-9).
shingle beaches, 387-90, (Fig.

249).
woodlands, 345-54, (Figs. 223-

7)-
Vegetative organs, 14.

reproduction, 140-2, 280.
Veins (see Vascular Bundles), 14,

67.
Venus' Fly-trap, 152, 366, (Fig.

234)-
Verbascum, 256.

Vernal-grass, 201, (Fig. 138), 368.
Vernation, 1 19.
Veronica, 256, 343, 378, 379,

380.
Verticillaster, 252.
Vetch, 144, 147, 190, 203, 246.
Bush, 341, (Fig. 220), 379.
Horseshoe, 368.
Vetchling, Yellow, 245.
Viburnum, 258.
Vicia, 246, 378, 379.
Vine, 98, 147.
Viola, 378.
Violet, 116, 119, 185-6, (Figs.

127-9), 203, 206, 216, (Fig.

151), 227, (Fig. 162), 235,

343-
Dog, 353.
Marsh, 348.
Sweet, 186.
Water, 249.
Yellow, 370.
Viper's Bugloss, 250, 379, 389.

Virginia Creeper, 108, 144, 147,

(Fig. 94).
Vivipary, 14 1-2.

Wallflower, 206, 238.
Walls, plants of, 344.
Wall-rue (Asplenium), 344.
Water, course of, in stem, 89.

need for, 49-50, 55, 95, 97,
102-3.

pollen transferred by, 375.
Water Buttercup, 371, (Figs.
238, 242).

Cress, 238, 343.

-cultures, 55-7, (Fig. 25).

-dispersed fruits, 223-4.

Lily, 157, (Fig. 105), 371, (Fig.
241).

weeds, 142.
Water-plants, 370-5. (Figs. 237-

43)-
aeration in, 372.
flowers of, 375.
invasion by, 374.
slime on, 373-4.
structure of, 372 (Figs. 242-3).
vegetative reproduction in,

374-5-
Water-stomata, 98.
Wax on leaves, 95-6.
Wayfaring Tree, 116, 225, 258,

349. 353-
Weeds, 376-80, (Fig. 244).
cornfield, 377-9.
meadow and pasture, 379-80.
Weigelia, 258.
Wheat, 30-2, (Figs. 12, 13), 84,

97, (Fig. 58), 126, 210, 214,

265.
Whin, 395.

Petty, 246.
Whorl, 127.
Wickens, 298.
Wicks, 125, 379.
Willows, 121, (Fig. 78), 160, 202,

204, 221, (Figs. 156-7), 235,

276-8, (Fig. 185), 294, 348,

376.
Creeping, 353.
Dwarf, 386.

Goat, 276, 278, (Fig. 185).
Pollard, 277.
White, 277.

440

INDEX

Willow-herb, 221, 379,

Hairy, 376.

Square-stemmed, 343, 376.
Wilting, 49-50, 96, 97.
Winged fruits, 24, (Fig. 9).
Winter Aconite, 238.
Winter buds, 374.
Wintergreen, Chickweed, 250,

353-
Woodbine, 258.
Woodlands, plants of, 345-54.
Wood-rush, Field, 204.
Woods, Alder-Carr, 353.

Alder- Willow, 352, 376.

Ash, 349, 353.

Beech, 353-4.

calcareous, 353-4.

Oak- Ash, 353.

Oak- Birch-Heath, 352.

Pedunculate Oak, 352.

Pine, 352-3.

Sessile Oak, 347-52, (Figs.

223-5)-
siliceous, 352-3.
types of, 352-4-
Wood Sorrel, 142, 149-50, (Fig.

99), 152, 154, 204, 228, (Fig.
162), 343.

Woody Nightshade, or Bitter-
sweet, 116, 182-3, (Fig- 125),
225.

Woundwort, Hedge, 254, 343.
Marsh, 254.

Xerophytes, 252, 318, 382, 386.
Xylem, 69.

Yarrow, 370, 380.

Yellow Rattle, 256, 359, 370, 379,

380.
Yew, 108, 149, (Fig. 97), 354.
Yorkshire Fog, 368, 370, 380.
Yucca, 266.

Zonation, 315-17, (Figs. 163, 208).
in hedge-bank, 337-8, (Fig.

218).
in water-plants, 372, (Figs.
237-4I)-
Zoophilous, 205.
Zoster a, 383.
Zygomorphic, 173.

Printed in England at the Oxford University Press

VI 6
forestry

Woodhead, Thorn s

The stud, f riants

0Hl

9 \993

PLEASE DO NOT REMOVE
SUPS FROM THIS POCKET

/779097)

UNIVERSITY OF TORONTO
LIBRARY

■: ,::,■", yr- .■■':< v:. -v.

Internet Archive Audio

Featured

Top

Images

Featured

Top

Software

Featured

Top

Books

Featured

Top

Video

Featured

Top

Mobile Apps

Browser Extensions

Archive-It Subscription

Save Page Now

Full text of "The study of plants; an introduction to botany and plant ecology"

See other formats