Digitized by the Internet Archive
in 2008 with funding from
Microsoft Corporation
http://www.archive.org/details/beginnersbotany0Obailuoft
pate - oe
ne
BEGINNERS’ BOTANY
\
*;
THE MACMILLAN COMPANY
NEW YORK + BOSTON + CHICAGO
SAN FRANCISCO
MACMILLAN & CO,, Limitep
LONDON + BOMBAY + CALCUTTA
MELBOURNE
THE MACMILLAN CO. OF CANADA, Lp,
TORONTO
BOUQUET OF BEARDED WHEAT
BEGINNERS BOTANY
BY
Eh BALLEY.
AUTHORIZED BY THE MINISTER OF EDUCATION
FOR ONTARIO
TORONTO
tHE MACMILLAN CO. OF CANADA, LIMITED
1921
3) Sol
CopyRIGHT, 1921
By THE MACMILLAN CO. OF CANADA LTD.
| PREFACE
In all teaching of plants and animals to beginners, the
plants themselves and the animals themselves should be
made the theme, rather than any amount of definitions and
of mere study in books. Books will be very useful in
guiding the way, in arranging the subjects systematically,
_ and in explaining obscure points; but if the pupil does not
know the living and growing plants when he has completed
his course in botany, he has not acquired very much that
is worth the while.
It is well to acquaint the beginner at first with the main
features of the entire plant rather than with details of its
parts. He should at once form a mental picture of what
the plant is, and what are some of its broader adaptations
to the life that it leads. In this book, the pupil starts with
the entire branch or the entire plant. It is sometimes said
that the pupil cannot grasp the idea of struggle for exist-
ence until he knows the names and the uses of the different
parts of the plant. This is an error, although well estab-
lished in present-day methods of teaching.
Another very important consideration is to adapt the
statement of any fact to the understanding of a beginner.
It is easy, for example, to fall into technicalities when dis.
cussing osmosis; but the minute explanations would mean
nothing to the beginner and their use would tend to con-
fuse the picture which it is necessary to leave in the pupil’s
mind. Even the use of technical forms of expression would
probably not go far enough to satisfy the trained physicist.
v
vi PREFACE
It is impossible ever to state the last thing about any
proposition. All knowledge is relative. What is very
elementary to one mind may be very technical and ad-
vanced to another. It is neither necessary nor desirable
to safeguard statements to the beginner by such qualifica-
tions as will make them satisfactory to the critical expert
in science. The teacher must understand that while
accuracy is always essential, the degree of statement is
equally important when teaching beginners.
The value of biology study lies in the work with the
actual objects. It is not possible to provide specimens for’
every part of the work, nor is it always desirable to do so;
for the beginning pupil may not be able to interest himself
in the objects, and he may become immersed in details
before he has arrived at any general view or reason of the
subject. Great care must be exercised that the pupil is
not swamped. Mere book work or memory stuffing is
useless, and it may dwarf or divert the sympathies of
active young minds.
The present tendency in secondary education is away
from the formal technical completion of separate subjects
and toward the developing of a workable training in the
activities that relate the pupil to his own life. In the
natural science field, the tendency is to attach less im-
portance to botany and zoology as such, and to lay greater
stress on the processes and adaptations of life as expressed
in plants and animals. Education that is not applicable,
that does not put the pupil into touch with the living know-
ledge and the affairs of his time, may be of less educative
value than the learning of a trade ina shop. We are begin-
ning to learn that the ideals and the abilities should be
developed out of the common surroundings and affairs
PREFACE Vil
of life rather than imposed on the pupil as a matter of
abstract unrelated theory.
It is much better for the beginning pupil to acquire a
real conception of a few central principles and points of
view respecting common forms that will enable him to tie
his knowledge together and organize it and apply it, than
to familiarize himself with any number of mere facts about
the lower forms of life which, at the best, he can know
only indirectly and remotely. If the pupil wishes to go
farther in later years, he may then take up special groups
and phases.
CHAPTER
ie
1
CONTENTS
No Two PLANTS OR PARTS ARE ALIKE , 4
THE STRUGGLE TO LIVE . ; A 5 A
SURVIVAL OF THE FIT : F . : A
PLANT SOCIETIES ‘ 5 , - : °
THE PLANT Bopy ; 5 : ; 5
SEEDS AND GERMINATION
THE Root — THE ForRMS oF Roots .
THE ROOT— FUNCTION AND STRUCTURE
THE STEM — KINDS AND FORMS — PRUNING
THE STEM—ITS GENERAL STRUCTURE . :
LEAVES— FORM AND POSITION
LEAVES — STRUCTURE AND ANATOMY
LEAVES — FUNCTION OR WORK
DEPENDENT PLANTS . . : : : :
WINTER AND DORMANT Bubs. % F
Bub PROPAGATION A : : - f :
How PLaAnts CLIMB
THE FLOWER —ITs PARTS AND FORMS
THE FLOWER — FERTILIZATION AND POLLINATION
FLOWER-CLUSTERS
FRUITS : q . . A F A ;
DISPERSAL OF SEEDS . 5 : : : .
PHENOGAMS AND CRYPTOGAMS . : 3 A
STUDIES IN CRYPTOGAMS . ° A ; .
ON fF H
BEGINNERS’ BOTANY
CHAPTER 1
NO TWO PLANTS OR PARTS ARE ALIFE
FIG. 1.— NO Two BRANCHES ARE ALIKE.
(Hemlock.)
IF one compares any two plants of
HOS: the same kind ever so closely, it will be
found that they differ from each other. The
. difference is apparent in size, form,’colour, mode
of branching, number of leaves, number of flowers, vigour,
season of maturity, and the like; or, in other words, all
plants and animals vary from an assumed or standard type.
If one compares any two branches or twigs on a tree, it
wili be found that they differ in size, age, form, vigour, and
in other ways (Fig. 1).
If one compares any two Jeaves, it will be found that
they are unlike in size, shape, colour, veining, hairiness,
markings, cut of the margins, or other small features. In
some cases (as in Fig. 2) the differences are so great as to
be readily seen in a small black-and-white drawing.
B I
2 BEGINNERS’ BOTANY
If the pupil extends his observation to animals, he
will still find the same truth; for probably xo two living
objects are exact duplicates. If any person finds two objects
that he thinks to be exactly alike, let him set to work to
Fic. 2.— No Two LEAVES ARE ALIKE.
discover the differences, remembering that xothing im
nature is so small or apparently trivial as to be overlooked.
Variation, or differences between organs and also be-
tween organisms, is one of the most significant facts in
nature.
SuGcEsTions.—The first fact that the pupil should acquire
about plants is that no two are alike. The way to apprehend this
great fact is to see a plant accurately and then to compare it with
NO TWO PLANTS OR PARTS ARE ALIKE 3
another plant of the same species or kind. In order to direct and
concentrate the observation, it is well to set a certain number of
attributes or marks or qualities to be looked for. 1. Suppose
any two or more plants of corn are compared in the following
points, the pupil endeavouring to determine whether the
parts exactly agree. See that the observation is close and
accurate. Allow no guesswork. Instruct the pupil to meas-
ure the parts when size is involved.
(1) Height of the plant.
(2) Does it branch? How many secondary stems or
from one root?
(3) Shade or colour.
(4) How many leaves.
‘fsuckers’
(5) Arrangement of leaves on stem.
(6) Measure length and breadth of six main leaves.
(7) Number and position of ears; colour of silks.
(8) Size of tassel, and number and size of its branches.
(9) Stage of maturity or ripeness of plant.
(10) Has the plant grown symmetrically, or has it been crowded
by other plants or been obliged to struggle for light or room?
(11) Note all unusual or interesting marks or features.
(12) Always make note of comparative vigour of the plants.
Note To TEACHER. — The teacher should always insist on fer-
sonal work by the pupil. Every pupil should anadle and study
the object by himself. Books and pictures are merely guides and
helps. So far as possible, study the plant or animal just where it
grows naturally.
Notebooks. — Insist that the pupils make full notes and preserve
these notes in suitable books. Note-taking is a powerful aid in
organizing the mental processes, and in insuring accuracy of obser-
vation and record. The pupil should draw what he sees, even
though he is not expert with the pencil. The drawing should not
be made for looks, but to aid the pupil in his orderly study of the
object ; it should be a means of self-expression.
CHAPTER II
THE STRUGGLE TO LIVE
Every plant and animal is exposed to unfavourable con-
ditions. It is obliged to contend with these conditions in
order to live.
No two plants or parts of plants are identically exposed
to the conditions in which they live. The large branches
FIG. 3.—A BATTLE FOR LIFE.
in Fig. 1 probably had more room and a better exposure
to light than the smaller ones. Probably no two of the
leaves in Fig. 2 are equally exposed to light, or enjoy
identical advantages in relation to the food that they re-
ceive from the tree.
Examine any tree to determine under what advantages
or disadvantages any of the limbs may live. Examine
similarly the different plants in a garden row (Fig. 3); or
the different bushes in a thicket; or the different trees in
a wood.
THE STRUGGLE TO LIVE 5
The plant meets its conditions by succumbing to them
(that is, by dying), or by adapting ttself to them.
The tree meets the cold by ceasing its active growth,
hardening its tissues, dropping its leaves. Many her-
baceous or soft-stemmed plants meet the cold by dying
to the ground and withdrawing all life into the root parts.
Some plants meet the cold by dying outright and provid-
ing abundance of seeds to perpetuate the kind next season.
Fic. 4.— THE REACH FOR LIGHT OF A TREE ON THE EDGE OF A WOOD.
Plants adapt themselves to light by growing toward it
(Fig. 4); or by hanging their leaves in such position that
they catch the light; or, in less sunny places, by expand-
ing their leaf surface, or by greatly lengthening their
stems so as to overtop their fellows, as do trees and vines.
The adaptations of plants will afford a fertile field of
study as we proceed.
6 BEGINNERS’ BOTANY
Struggle for existence and adaptation to conditions are
among the most significant facts in nature.
The sum of all the conditions in which a plant or an ani-
mal is placed is called its environment, that is, its surround-
ings. The environment comprises the conditions of climate,
soil, moisture, exposure to light, relation to food supply,
contention with other plants or animals. Zhe organism
adapts itself to its environment, or else tt weakens or dates.
Every weak branch or plant has undergone some hardship
that it was not wholly able to withstand.
SuGGESTIONS.—The pupil should study any plant, or branch of a
plant, with reference to the position or condition under which it
grows, and compare one plant or branch with another. With animals,
it is common knowledge that every animal is alert to avoid or to
escape danger, or to protect itself. 2. It is well to begin with a
branch of a tree, as in Fig. 1. Note that no two parts are alike (Chap.
T). Note that some are large and strong and that these stand far-
thest toward light and room. Some are very small and weak, barely
able to live under the competition. Some have died. The pupil can
easily determine which of the dead branches perished first. He should
take note of the position or place of the branch on the tree, and
determine whether the greater part of the dead twigs are toward the
centre of the tree top or toward the outside of it. Determine whether
accident has overtaken any of the parts. 3. Let the pupil examine
the top of any thick old apple tree, to see whether there is any
struggle for existence and whether any limbs have perished. 4. If
the pupil has access to a forest, let him determine why there are no
branches on the trunks of the old trees. Examine a tree of the
same kind growing in an open field. 5. A row of lettuce or other
plants sown thick will soon show the competition between plants.
Any fence row or weedy place will also show it. Why does the
farmer destroy the weeds among the corn or potatoes? How does
the florist reduce compet on ¢o ats iowest terms? what is the result?
CHAPTER, IIT
THE SURVIVAL OF THE FIT
Tue plants that most perfectly meet their conditions are
able to persist. They perpetuate themselves. ‘Vheir off-
spring are likely to inherit some of the attributes that
enabled them successfully to meet the battle of life. Zhe
fit (those best adapted to their conditions) Zend zo survive.
Adaptation to conditions depends on the fact of varia-
tion; that is, if plants were perfectly rigid or invariable
(all exactly alike) they could not meet new conditions.
Conditions are necessarily new for every organism. /¢ is
impossible to picture a perfectly inflexible and stable succes-
sion of plants or animals.
Breeding. — A/an 7s able to modify plants and animals.
All our common domestic animals are very unlike their
original ancestors. So all our common and _long-culti-
vated plants have varied
from their ancestors. Even
in some plants that have
been in cultivation less than
a century the change is
marked: compare the com-
mon black-cap raspberry
with its common wild ances-
tor, or the cultivated black- Fic. 5.—DestraBLE AND UNDESIRABLE
berry with the wild form. TYPES OF COTTON PLANTS. Why?
By choosing seeds from a plant that pleases him, the
breeder may be able, under given conditions, to produce
7
8 BEGINNERS’ BOTANY
on
tion. A some-
what similar
process pro-
ceeds in wild
nature, and it
is then known
as natural se-
lection.
SUGGESTIONS.
—6. Every pu-
pil should un-
dertake at least
FIG. 6.— FLAX BREEDING.
A ‘sa plant grown for seed production;
one simple ex-
Why?
DP for fibre production.
periment in se-
lection of seed. He may select kernels from the
best plant of corn in the field, and also from the
poorest plant,—having reference not so much to
mere incidental size and vigour of the plants that
may be due to accidental conditions in the field,
as to the apparently constitutional strength and
size, number of ears, size of ears, perfectness of
ears and kernels, habit of the plant as to sucker-
ing, and the like. The seeds may be saved and
sown the next year. Every crop can no doubt
be very greatly improved by a careful process
of selection extending over a series of years.
Crops are increased in yield or’ efficiency in three
ways: better general care; enriching the land in
which they grow; attention to breeding.
numbers of plants with more
or less of the desired quali-
ties; from the best of these,
he may again choose; and so
until the race becomes
greatly improved (Figs. 5, 6,
7). This process of continu-
ously choosing the most suita-
ble plants is known as selec-
FIG. 7.— BREED-
ING.
A, effect from breed-
ing from smallest
grains (after four
years), average
head; 3B, result
from breeding from
the plumpest and
heaviest grains
(after four years),
average head,
CHAP PER BY.
PLANT SOCIETIES
In the long course of time in which plants have been
accommodating themselves to the varying conditions in
which they are obliged to grow, hey have become adapted
to every different environment. Certain plants, therefore,
may, live together or near each other, all enjoying the
same general conditions and surroundings. These aggre-
gations of plants that are adapted to similar general con-
ditions are known as plant societies.
Moisture and temperature are the leading factors in
determining plant societies. The great geographical
societies or aggregations of the plant world may con-
veniently be associated chiefly with the moisture supply,
as: wet-region societies, comprising aquatic and bog
vegetation (Fig. 8); arid-region societies, comprising desert
and most sand-region vegetation; wm7zd-region soctettes,
comprising the mixed vegetation in intermediate regions
(Fig. 9), this being the commonest type. Much of the
characteristic scenery of any place is due to its plant
societies. Arid-region plants usually have small and hard
jieaves, apparently preventing too rapid loss of water.
Usually, also, they are characterized by stiff growth, hairy
covering, spines, or a much-contracted plant-body, and
often by large underground parts for the storage of water.
Plant societies may also be distinguished with reference
to latitude and temperature. There are “vopical socteties,
temperate-region societies, boreal or cold-region socteties.
9
IO BEGINNERS’ BOTANY
With reference to altitude, societies might be classified
as lowland (which are chiefly wet-region), zx/ermediate
(chiefly mid-region), szbalpine or mid-mountain (which are
chiefly boreal), a/pine or high-mountain.
The above classifications have reference chiefly to great
geographical floras or societies. But there are soczetzes
within societies. There are small societies coming within
the experience of every person who has ever seen plants
Fic. 8.— A WET-REGION SOCIETY.
growing in natural conditions. There are roadside, fence-
row, lawn, thicket, pasture, dune, woods, cliff, barn-yard
societies. Lvery different place has its characteristic vegeta-
tion. Note the smaller societies in Figs. 8 and 9g. In the
former is a water-lily society and a cat-tail society. In
the latter there are grass and bush and woods societies.
Some Details of Plant Societies. — Societies may be com-
posed of scattered and intermingled plants, or of dense
clumps or. groups of plants. Dense clumps or groups are
usually made up of one kind of plant, and they are then
PLANT SOCIETIES II
called colonies. Colonies of most plants are transient:
after a short time other plants gain a foothold amongst
them, and an intermingled society is the outcome. Marked
exceptions to this are grass colonies and forest colonies, in
which one kind of plant may hold its own for years and
centuries.
In a large newly cleared area, plants usually first estab-
lish themselves in dense colonies. Note the great patches
FIG. 9.—A MID-REGION SOCIETY.
of nettles, jewel-weeds, smart-weeds, clot-burs, fire-weeds
in recently cleared but neglected swales, also the fire-weeds
in recently burned areas, the rank weeds in the neglected
garden, and the ragweeds and May-weeds along the re-
cently worked highway. The competition amongst them-
selves and with their neighbours finally breaks up the
colonies, and a mixed and intermingled flora is generally
the result.
In many parts of the world the general tendency of neg-
lected areas is to run into forest. All plants rush for the
12 BEGINNERS’ BOTANY
cleared area. Here and there bushes gain a foothold.
Young trees come up; in time these shade the bushes and
gain the mastery. Sometimes the area grows to poplars
or birches, and people wonder why the original forest trees
do not return ; but these forest trees may be growing unob-
served here and there in the tangle, and in the slow pro-
cesses of time the poplars perish — for they are short-lived
—and the original forest may be replaced. Whether one
kind of forest or another returns will depend partly on the
kinds that are most seedful in that vicinity and which,
therefore, have sown themselves most profusely. Much
depends, also, on the kind of undergrowth that first springs
up, for some young trees can endure more or less shade
than others.
Some plants associate. They grow together. This is
possible largely because they diverge or differ in charac-
ter. Plants asso-
ciate in two ways:
by growing side by
side; by growing
above or beneath.
In sparsely popu-
lated societies,
plants may grow
alongside each
other. In most
cases, however,
FIG, I0.— OVERGROWTH AND UNDERGROWTH IN thereis overgrowth
THREE SERIES, — trees, bushes, grass.
and wudergrowth :
one kind grows beneath another. Plants that have be-
come adapted to shade are usually undergrowths. In a cat-
tail swamp, grasses and other narrow-leaved plants grow
in the bottom, but they are usually unseen by the casual
PLANT SOCIETIES 13
observer. Note the undergrowth in woods or under trees
(Fig. 10). Observe that in pine and spruce forests there
is almost no undergrowth, partly because there is very little
light.
On the same area the societies may differ at different
times of the year. There are spring, summer, and fall soci-
eties. The knoll which is cool with grass and strawber-
ries in June may be aglow with goldenrod in September.
If the bank is examined in May, look for the young plants
that are to cover it in July and October; if in Septem-
ber, find the dead stalks of the flora of May. What suc-
ceeds the skunk cabbage, hepaticas, trilliums, phlox, violets,
buttercups of spring? What precedes the wild sunflowers,
ragweed, asters, and goldenrod of fall ?
The Landscape.— To a large extent the colour of the land-
scape is determined by the character of the plant societies.
Evergreen societies remain green, but the shade of green
varies from season to season; it is bright and soft in
spring, becomes dull in midsummer and fall, and assumes
a dull yellow-green or a black-green in winter. Deciduous
societies vary remarkably in colour—from the dull browns
and grays of winter to the brown greens and olive-greens
of spring, the staid greens of summer, and the brilliant
colours of autumn.
The autumn colours are due to intermingled shades of
green, yellow and red. The coloration varies with the kind
of plant, the special location, and the season. Even in the
same species or kind, individual plants differ in colour ; and
this individuality usually dstinguishes the plant year by
year. That is, an oak which is maroon red this autumn is
likely to exhibit that range of colour every year. The au-
tumn colour is associated with the natural maturity and
death of the leaf, but it is most brilliant in long and open
14 BEGINNERS’ BOTANY
falls — largely because the foliage ripens more gradually
and persists longer in such seasons. It is probable that
the autumn tints are of no utility tothe plant. Autumn
colours are not caused by frost. Because of the long, dry
falls and the great variety of plants, the autumnal colour of
the American landscape is phenomenal.
Ecology. — The study of the relationships of plants and
animals to each other and to seasons and environments is
known as ecology (still written @co/ogy in the dictionaries).
It considers the habits, habitats, and modes of life of liv-
ing things—the places in which they grow, how they
migrate or are disseminated, means of collecting food,
their times and seasons of flowering, producing young,
and the like.
SuGGESTIONS. — One of the best of all subjects for school instruc-
tion in botany is the study of plant societies. It adds definiteness
and zest to excursions. 7, Let each excursion be confined to one
or two societies. Visit one day a swamp, another day a forest,
another a pasture or meadow, another a roadside, another a weedy
field, another a cliff or ravine. Visit shores whenever possible.
Each pupil should be assigned a bit of ground — say 10 or 20 ft.
square — for special study. He should make a list showing (1)
how many kinds of plants it contains, (2) the relative abundance
of each. The lists secured in different regions should be com-
pared. It does not matter greatly if the pupil does not know all
the plants. He may count the kinds without knowing the names.
It is a good plan for the pupil to make a dried specimen of each
kind for reference. The to discover why
the plants grow as they do. Note what kinds of plants grow next
each other; and which are undergrowth and which overgrowth ;
and which are erect and which wide-spreading. Challenge every
plant society.
CHAPTER V
THE PLANT BODY
The Parts of a Plant. — Our familiar plants are made up
cf several distinct parts. The most prominent of these
parts are voot, stem, leaf, flower, fruit, and seed. Familiar
plants differ wonderfully in size and shape, — from fragile
mushrooms, delicate waterweeds and pond-scums, to float-
ing leaves, soft grasses, coarse weeds, tall bushes, slender
climbers, gigantic trees, and hanging moss.
The Stem Part.— In most plants there is a main central
part or shaft on which the other or secondary parts are
borne. This main part is the plant axis. Above ground,
in most plants, the main plant axis bears the branches,
leaves, and flowers ; below ground, it bears the roots.
The rigid part of the plant, which persists over winter
and which is left after leaves and flowers are fallen, is the
framework of the plant. The framework is composed of
both root and stem. When the plant is dead, the frame-
work remains for a time, but it slowly decays. The dry
winter stems of weeds are the framework, or skeleton of
the plant (Figs. 11 and 12). The framework of trees is
the most conspicuous part of the plant.
The Root Part. — The root bears the stem at its apex,
but otherwise it normally dears only root-branches. The
stem, however, dears leaves, flowers, and fruits. Those
living surfaces of the plant which are most exposed to
light are green or highly coloured. The root tends to grow
downward, but the stem tends to grow upward toward light
1b
16 BEGINNERS’ BOTANY
and air. The plant is anchored or fixed in the soil by the
roots. Plants have been called “ earth parasites.”’
The Foliage Part. — The leaves precede the flowers in
point of time or life of the plant. Zhe flowers always
precede the fruits and seeds. Many plants die when the ©
seeds have matured. The whole mass of leaves of any
plant or any branch is
known as its /olzage.
In some cases, as in
crocuses, the flowers °
seem to precede the
leaves; but the leaves
that made the food for
these flowers grew the
preceding year.
The Plant Generation.
— The course of a
plant’s life, with all the
events through which
the plant naturally
passes, is known as
the plant’s life-history.
The life-history em-
FIG. 11.— PLANT OF A FIG. 12.— FRAME- braces various stages,
WILD SUNFLOWER. WORK OF FIG, II.
or epochs, as dormant
seed, germination, growth, flowering, fruiting. Some plants
run their course in a few weeks or months, and some live
for centuries.
The entire life-period of a plant is called a generation.
It is the whole period from birth to normal death, without
reference to the various stages or events through which it
passes.
A generation begins with ¢he young seed, not with germi-
THE PLANT BODY 17
nation. Jt ends with death — that is, when no life is left
in any part of the plant, and only the seed or spore
remains to perpetuate the kind. In a bulbous plant, as a
lily or an onion, the generation does not end until the bulb
dies, even though the top is dead.
When the generation is of only one season’s duration,
- the plant is said to be annual. When it is of two seasons,
it is biennial. Biennials usually bloom the second year.
When of three or more seasons, the plant is perennial.
Examples of annuals are pigweed, bean, pea, garden sun-
flower; of biennials, evening primrose, mullein, teasel; of
perennials, dock, most meadow grasses, cat-tail, and all
shrubs and trees.
Duration of the Plant Body. — Plant structures which
are more or less soft and which die at the close of the
season are said to be herbaceous, in contradistinction to
being ligneous or woody. A plant which is herbaceous to
the ground is called an herb; but an herb may have a
woody or perennial root, in which case it is called an
herbaceous perennial. Annual plants are classed as herbs.
Examples of herbaceous perennials are buttercups, bleed-
ing heart, violet, waterlily, Bermuda grass, horse-radish,
dock, dandelion, goldenrod, asparagus, rhubarb, many
wild sunflowers (Figs. 11, 12).
Many herbaceous perennials have short generations.
They become weak with one or two seasons of flowering
and gradually die out. Thus, red clover usually begins to
fail after the second year. Gardeners know that the best
bloom of hollyhock, larkspur, pink, and many other plants,
is secured when the plants are only two or three years
old.
Herbaceous perennials which die away each season to
bulbs or tubers, are sometimes called pseud-annuals (that
c
18 BEGINNERS’ BOTANY
is, false annuals). Of such are lily, crocus, onion, potato,
and bull nettle.
True annuals reach old age the first year. Plants which
are normally perennial may become annual in a shorter-
season climate by being killed by frost, rather than by dying
naturally at the end of a season of growth. They are cli-
matic annuals. Such plants are called plur-annuals in the
short-season region. Many tropical perennials are plur-
Ties
IN
h'y;
Ka
FD a
TACs ST
Zi
Fic. 13.—A SHRUB OR BUSH. Dogwood osier,
annuals when grown in the north, but they are treated as
true annuals because they ripen sufficient of their crop the
same season in which the seeds are sown to make them
worth cultivating, as tomato, red pepper, castor bean,
cotton. Name several vegetables that are planted in
gardens with the expectation that they will bear till frost
comes.
Woody or ligneous plants usually live longer than
herbs. Those that remain low and produce several or
THE PLANT BODY 19
many similar shoots from the
base are called shrubs, as lilac,
rose, elder, osier(Fig. 13). Low
and thick shrubs are bushes.
Plants that produce one main
trunk anda more or lesselevated
head are trees (Fig. 14). All
shrubs and trees are perennial.
Every plant makes an effort
to propagate, or to perpetuate its
kind; and, as far as we.can
see, this is the end for which
the plant itself lives. Zhe seed
Ss the final pr
LOSES je Ewe, oduct of Fic. 14.—A TREE. The weeping
the plant. birch,
%
o
Sys?
So atta
~
SUGGESTIONS. — 8 The teacher may assign each pupil to one
plant in the school yard, or field, or in a pot, and ask him to bring
out the points in the lesson. 9. The teacher may put on the
board the names of many common plants and ask the pupils to
classify into annuals, pseud-annuals, plur-annuals (or climatic
annuals), biennials, perennials, herbaceous perennials, ligneous
perennials, herbs, bushes, trees. Every plant grown on the farm
should be so classified: wheat, oats, corn, buckwheat, timothy,
strawberry, raspberry, currant, tobacco, alfalfa, flax, crimson clover,
hops, cowpea, field bean, sweet potato, peanut, radish, sugar-cane,
barley, cabbage, and others. Name all the kinds of trees you
know.
CHAPTER VI
SEEDS AND GERMINATION
THE seed contains a mniature plant, or embryo. The
embryo usually has three parts that have received
names: the stemlet, or caulicle; the seed-leaf, or cotyledon
(usually I or 2); the bud, or plumule, lying between or
above the cotyledons. These parts are well
seen in the common bean (Fig. 15), particu-
larly when the seed has been soaked for a
few hours. One of the large cotyledons —
FIG. 15.- PARTS ae Z
OF THE Bean, COMprising half of the bean —is shown at
R, cotyledon; 0, A. The caulicle is at O. The plumule is
setae shown at A. The cotyledons are attached
ee: to the caulicle at /’: ¢hzs point may be taken
as the first node or joint. ;
The Number of Seed-leaves..— All plants having fo
seed-leaves belong to the group called dicotyledons. Such
seeds in many cases split readily in halves, e.g. a bean.
Some plants have only ove seed-leaf in a seed. They
form a group of plants called monocotyledons. Indian
corn is an example of a plant with only one seed-leaf:
a grain of corn does not split into ha'ves as a bean does.
Seeds of the pine family contain more than two cotyledons,
but for our purposes they may be associated with the dicoty-
ledons, although really forming a different group.
These two groups-—the dicotyledons and the mono-
cotyledons — represent two great natural divisions of the
vegetable kingdom. The dicotyledons contain the woody
20
SEEDS AND GERMINATION 21
bark-bearing trees and bushes (except conifers), and most
of the herbs of temperate climates except the grasses,
sedges, rushes, lily tribes, and orchids. The flower-parts
are usually in fives or multiples of five, the leaves mostly
netted-veined, the bark or rind distinct, and the stem often
bearing a pith at the centre. The monocotyledons usually
have the flower-parts in threes or multiples of three, the
leaves long and parallel-veined, the bark not separable,
. and the stem without a central pith.
Every seed is provided with food to support the germinat-
ing plant. Commonly this food is starch. The food may
be stored zz the cotyledons, as in bean, pea, squash ; or owt-
side the cotyledons, as in castor bean, pine, Indian corn.
When the food is outside or around the embryo, it is
usually called endosperm.
Seed-coats; Markings on Seed. —The embryo and en-
dosperm are inclosed within a covering made of two or
more layers and known as the seed-coats.
Over the point of the caulicle is a minute
hole or a thin place in the coats known as
the micropyle. This is the point at which Fy. 16,—ExTeR-
the pollen-tube entered the forming ovule chp ai oe
and through which the caulicle breaks. in
germination. The micropyle is shown at J/ in Fig. 16.
The scar where the seed broke from its funiculus (or stalk
that attached it to its pod) is named the hilum. It occu-
pies a third of the length of the bean in Fig. 16. The
hilum and micropyle are always present in seeds, but they
are not always close together. In many cases it is difficult
to identify the micropyle in the dormant seed, but its loca-
tion is at once shown by the protruding caulicle as germi-
nation begins. Opposite the micropyle in the bean (at the
other end of the hilum) is an elevation known as the raphe.
32 BEGINNERS’ BOTANY
This is formed by a union of the funiculus, or seed-stalk,
with the seed-coats, and through it food was transferred
for the development of the seed, but it is now functionless.
Seeds differ wonderfully in size, shape, colour, and other
characteristics. They also vary in longevity. These
characteristics are peculiar to the species or kind. Some
seeds maintain life only a few weeks or even days, whereas
others will “keep” for ten or twenty years. In special
cases, seeds have retained vitality longer than this limit,
but the stories that live-seeds, several thousand years old,
have been taken from the wrappings of mummies are un-
founded.
Germination. — The embryo is not dead; it is only dor-
mant. When supplied with moisture, warmth, and oxygen
(azr), zt awakes and grows: this growth is germination.
The embryo lives for a time on the stored food, but gradu-
ally the plantlet secures a foothold in the soil and gathers
food for itself. When the plantlet is finally able to shift
for itself, germination ts complete.
Early Stages of Seedling. — The germinating seed first
absorbs water, and swells. The starchy matters gradually
become soluble. The seed-coats are ruptured, the caulicle
and plumule emerge. During this process the seed
vespires freely, throwing off carbon dioride (CO,).
The caulicle usually elongates, and from its lower end
roots are emitted. The elongating caulicle is known as
the hypocotyl (“below the cotyledons’’). That is, the
hypocotyl is that part of the stem of the plantlet lying
between the roots and the cotyledon. Zhe general direc-
tion of the young hypototyl, or emerging caulicle, is down-
wards. As soon as roots form, it becomes fixed and its
subsequent growth tends to raise the cotyledons above the
ground, as in the bean, When cotyledons rise into the
SEEDS AND GERMINATION 23
air, germination is said to be epigeal (“ above the earth es
Bean and pumpkin are examples. When the hypocotyl
does not elongate greatly |
and the cotyledons remain
under ground, the germin-
ation is hypogeal (‘‘be-
Heath ‘the’ earth’). Pea
and scarlet runner bean
are examples (Fig. 48).
When the germinating
seed lies on a hard sur-
FIG. 17. — PEA. Grotesque forms assumed
face, as on closely com- when the roots cannot gain entrance to
the soil,
pacted soil, the hypocotyl
and rootlets may not be able to secure a foothold and they
assume grotesque forms (Fig. 17). Try this with peas and
beans.
The first internode (‘between nodes’’) above the coty-
ledons is the epicotyl. It elevates the plumule into the
air, and the plumutle-leaves expand into the first true leaves
of the plant. These first true leaves, however, may be
very unlike the later leaves in shape.
Germination of Bean. — The common bean, as we have
seen (Fig. 15), has cotyledons that occupy all the space
== inside the seed-coats. When the hy-
CBs, pocotyl, or elongated caulicle, emerges,
I) the plumule-leaves have begun to en-
pee eae es large, and to unfold (Fig. 18). The
or Germinatinc hypocotyl elongates rapidly. One end
Set agi of it is held by the roots. The other
ING Cauticte anp is held by the seed-coats in the soil.
che It therefore takes the form of a loop,
and the central part of the loop “comes. up” first (a, Fig.
19). Presently the cotyledons come out of the seed-coats,
24 BEGINNERS’ BOTANY
and the plant straightens and the
cotyledons expand. These coty-
ledons, or “‘ halves of the bean,”
persist for some time (4, Fig.
19). They often become green
and probably perform some
function of foliage. Because of
its large size, the Lima bean
shows all these parts well.
Dey og Bes Germination of Castor Bean. —
BEAN. In the castor bean the hilum
and micropyle are at the smaller end
(Fig. 20). The bean “comes up” with a
loop, which indicates that the hypocotyl
FIG. 20. — SPROUT.
greatly elongates. On examining germin- ING OF CASTOR
: : : BEAN.
ating seed, however, it will be found
that the cotyledons are contained inside a fleshy body,
or sac (a, Fig. 21). This sac is the endosperm. Against
its inner surface the thin, veiny coty-
ledons are very closely pressed, ab-
FIG. 22.— CASTOR
FIG. 21.— GERMINA- BEAN. FIG. 23. — GERMINATION
TION OF CASTOR BEAN. Endosperm at a, a: coty- COMPLETE IN CASTOR
Endosperm at a. ledons at 4. BEAN.
sorbing its substance (Fig. 22). The cotyledons increase
in size as they reach the air (Fig. 23), and become func-
tional leaves.
SEEDS AND GERMINATION 25
Germination of Monocotyledons.— Thus far we have stud.
ied dicotyledonous seeds ; we may now consider the mono-
cotyledonous group. Soak kernels of corn. Note that
the micropyle and hilum are at the smaller end (Fig. 24).
Make a longitudinal section through the
narrow diameter; Fig. 25 shows it. The
FIG, 25.— KERNEL
FIG. 24.—SPROUT- OF INDIAN CORN.
FIG. 26.—INDIAN
ING INDIAN CORN, Caulicleat 6: couple: CORN. .
Hilum at 4; micro- don at a; plumule Caulicle at c; roots emerging at
pyle at @. at Z. m; plumule at Z.
single cotyledon is at a, the caulicle at 6, the plumule
at p. The cotyledon remains in the seed. The food is
stored both in the cotyledon and as endosperm, chiefly the
latter. The emerging shoot is the plumule, with a sheath-
ing leaf (f, Fig. 26). The root is emitted from the tip of
, the caulicle, c. The caulicle is held in a sheath
(formed mostly from the seed-coats), and some of
the roots escape through the upper end
of this sheath (m, Fig. 26). The
eee epicotyl elongates, particularly if
Uitn the seed is planted
— yi -deep’or if it-as
kept for a time
Fic. 27. — INDIA} : :
ear ee confined: In Fig.
o, plumule; x to J, epicotyl. 5
27 the epicotyl has
elongated from 7 tog. The true plumule-leaf is at 0, but
other leaves grow from its sheath. In Fig. 28 the roots
are seen emerging from the two ends of the caulicle-
26 BEGINNERS’ BOTANY
sheath, c, #; the epicotyl has grown to /; the first plu.
mule-leaf is at a.
In studying corn or other fruits or seeds, the pupil should
note how the seeds are arranged, as on the cob. Count the
rows on a corn cob. Odd or
even innumber? Always the
same number? The silk is
the style: find where it was
attached to the kernel. Did
the ear. have any coverings ?
Explain. Describe colours and
markings of kernels of corn;
and of peas, beans, castor
bean.
Gymnosperms. — The seeds
in the pine cone, not being
inclosed in a_ seed-vessel,
readily fall out when the cone
dries and the scales separate.
Hence it is difficult to find
cones with seeds in them after
autumn has passed (Fig. 29).
The cedar is also a gymno-
sperm.
Remove a scale from a
FIG, 28.— GERMINATION IS COM- pine cone and draw it and
PLETE. .
ee i the seeds as they lie in place
A; top of epicotyl; 0, plumule-leaf;
m, roots; c, lower roots. on the upper side of the scale.
Examine the seed, preferably with a magnifying glass. Is
there a hilum? The micropyle is at the bottom or little
end of the seed. Toss a seed upward into the air. Why
does it fall so slowly? Can you explain the peculiar whirl-
ing motion by the shape of the wing? Repeat the ex-
SEEDS AND GERMINATION 2)
periment in the wind. Remove the
wing from a seed and toss it and an
uninjured seed into the air together.
What do you infer from these ex-
periments ?
SUGGESTIONS. — Few subjects con-
nected with the study of plant-life are so
useful in schoolroom demonstrations as
germination. ‘The pupil should prepare
the soil, plant the seeds, water them, and
care for the plants. 10. Plant seeds in
pots or shallow boxes. The box should
not be very wide or long, and not over
four inches deep. Holes may be bored
in the bottom so it will not hold water.
Plant a number of squash, bean, corn,
pine, or other seeds about an inch deep
in damp sand or pine sawdust in this
box. The depth of planting should be
two to four times the diameter of the
seeds. Keep the sand or sawdust moist
but not wet. If the class is large, use
several boxes, that the supply of speci-
mens may be ample. Cigar boxes and
chalk boxes are excellent for individual
pupils. It is well to begin the planting
of seeds at least ten days in advance of
the lesson, and to make four or five differ-
ent plantings at intervals. A day or two Fy, 29.—ConEs oF HEM-
before the study is taken up, put seeds LOCK (ABOVE), WHITE
to soak in moss or cloth. The pupil PINE, PITCH PINE.
then has a series from swollen seeds to
complete germination, and all the steps can be made out. Dry
seeds should be had for comparison. [If there.is no special room
for laboratory, nor duplicate apparatus for every pupil, each ex-
periment may be assigned to a committee of two pupils to watch
in the schoolroom. 11. Good seeds for study are those detailed
in the lesson, and buckwheat, pumpkin, cotton, morning glory,
radish, four o’clock, oats, wheat. It is best to use familiar seeds
of farm and garden. Make drawings and notes of all the events
_in the germination. Note the effects of unusual conditions, as
planting too deep and too shallow and different sides up. For
hypogeal germination, use the garden pea, scarlet-runner, or Dutch
ab BEGINNERS’ BOTANY
ease-knife bean, acorn, horse-chestnut. Squash seeds are excellent
for germination studies, because the cotyledons become green and
leafy and germination is rapid. Onion is excellent, except that it
germinates too slowly. In order to study the root development of
germinating plantlets, it is well to provide a deeper box with a glass
side against which the seeds are planted. 12. Observe the germina-
tion of any common seed about the house premises. When elms, oaks,
pines, or maples are abundant, the germination of their seeds may
be studied in lawns and along fences. 13. When studying germina-
tion the pupil should note the differences in shape and size between
cotyledons and plumule leaves, and between plumule leaves and the
normal leaves (Fig. 30). Make drawings. 14. Make the tests de-
scribed in the introductory experiments with bean, corn, the castor
bean, and other seed for starch and proteids. Test flour, oatmeal,
rice, sunflower, four o’clock,
various nuts, and any other
seeds obtainable. Record your
results by arranging the seeds
in three classes, 1. Much starch
(colour blackish or purple). 2.
Little starch (pale blue or
greenish), 3. No starch (brown
or yellow). 15- Rate of
growth of seedlings as affect-
ed by differences in tempera-
ture. Pack soft wet paper to the depth of an inch in the bottom of
four glass bottles or tumblers. Put ten soaked peas or beans into
each. Cover each securely and set them in places having different
temperatures that vary little. (A furnace room, a room with a stove,
a room without stove but reached by sunshine, an unheated room
not reached by the sun). Take the temperatures occasionally with the
thermometer to find difference in temperature. The tumblers in
warm places should be covered very tightly to prevent the germination
from being retarded by drying out. Record the number of seeds
which sprout in each tumbler within 1 day, 2 days, 3 days, 4 days,
etc. 16. Is air necessary for the germination and growth of seed-
lings? Place damp blotting paper in the bottom of a bottle and
fill it three-fourths full of soaked seeds, and close it tightly with a
rubber stopper or oiled cork. Prepare a ‘‘check experiment’’ by
having another bottle with all conditions the same except that it
is covered loosely that air may have access to it, and set the bottles
side by side (why keep the bottles together?), Record results as in the
FIG. 30. — MUSKMELON SEEDLINGS, with
the unlike seed-leaves and true leaves.
SEEDS AND GERMINATION 29
preceding experiment. 17. What is the nature of the gas given off
by germinating seeds? Fill a tin box or large-necked bottle with
dry beans or peas,then add water; note how much they swell. Secure
two fruit jars. Fill one of them a third full of beans and keep them
moist. Allow the other to remain empty. In a day or two insert
a lighted splinter or taper into each. In the empty jar the taper
burns: it contains oxygen. In the seed jar the taper goes out: the
air has been replaced by carbon dioxide. The air in the bottle may
be tested for carbon dioxide by removing some of it with a rubber
bulb attached to a glass tube (or a fountain-pen filler) and bubbling
it through lime water. 18. Temperature. Usually there is a percep-
tible rise in temperature in a mass of germinating seeds. This rise
may be. tested with a thermometer. 19. Interior of seeds. Soak
seeds for twenty-four hours and remove the coat. Distinguish the
embryo from the endosperm. Test with iodine. 20. Of what utility
is the food in seeds? Soak some grains of corn overnight and re-
move the endosperm, being. careful not to injure the fleshy cotyledon.
Plant the incomplete and also some complete grains in moist sawdust
and measure their growth at intervals. (Boiling the sawdust will
destroy moulds and bacteria which might interfere with experiment. )
Peas or beans may be sprouted on damp blotting paper; the coty-
ledons of one may be removed, and this with a normal seed equally
advanced in germination may be placed on a. perforated cork floating
in water in a jar so that the roots extend into the water. Their
growth may be observed for several weeks. 21. Effect of darkness on
seeds and seedlings. A box may be placed mouth downward over
a smaller box in which seedlings are growing. The empty box should
rest on half-inch blocks to allow air to reach the seedlings. Note
any effects on the seedlings of this cutting off of the light. An-
other box of seedlings not so covered may be used as a check. Lay
a plank on green grass and after a week note the change that takes
place beneath it. 22. Seedling of pine. Plant pine seeds. Notice
how they emerge. Do the cotyledons stay in the ground? How many
cotyledons have they? When do the cotyledons get free from the
seed-coat? What is the last part of the cotyledon to become free?
Where is the growing point or plumule? How many leaves appear at
once? Does the new pine cone grow on old wood or on wood formed
the same spring with the cone? Can you always find partly grown
cones on pine trees in winter? Are pine cones when mature on two-
year-old wood? How long do cones stay on a tree after the seeds
have fallen out? What is the advantage of the seeds falling hefore
the cones? 23. Home experiments. If desired, nearly all of the fore-
30 BEGINNERS’ BOTANY
going experiments may be tried at home. The pupil can thus make
the drawings for the notebook at home.
Be ee toward the rind at certain places? Compare
their course with the strands shown in Fig. 70. The woody
strands consist chiefly of tough fibrous cells that give rigidity
THE STEM—ITS GENERAL STRUCTURE 61
and strength to the plant, and of long tubular interrupted
canals that serve to convey sap upward from the root and to
convey food downward from the leaves to the stem and the
roots.
Monocotyledons, as shown by fossils, existed before
dicotyledons appeared, and it is thought that the latter
were developed from ancestors of the
former. It will be interesting to trace
the relationship in stem structure. It
will first be necessary to learn something
of the structure of the wood strand.
Wood Strand in Monocotyledons and
Dicotyledons. — Each wood strand (or 7477 DIAGRAM OF
fibro-vascular bundle) consists of two — FIBRO-vascuLAR
parts —the bast and the wood proper. ia aaa
RooT, showing the
The wood is on the side of the strand wood (*) and bast
(/) separated.
toward the centre of the stem and con-
tains large tubular canals that take the watery sap upward
from the roots. The bast is on the side toward the bark,
and contains fine tubes
through which diffuses
the dense sap contain-
ing digested food from
the leaves. In the root
(Fig. 71) the bast and
the wood are separate,
so that there are /¢wo
kinds of strands.
In monocotyledons,
as already said, the
strands (or bundles) ave
FIG. 72.— PART OF CROSS-SECTION OF ROOT-
STOCK OF ASPARAGUS, showing a few fibro-
vascular bundles. An endogenous stem. usually scattered in the
stem with no definite arrangement (Figs. 72, 73). In
dicotyledons the strands, or bundles, ave arranged in a
62 BEGINNERS’ BOTANY
FIG. 74. — DICOTYLEDONOUS STEM OF ONE YEAR AT LEFT
WITH FIVE BUNDLES, and a two-year stem at right.
o, the pith; c, the wood part; 6, the bast part; @, one year’s growth,
ving. As the dicotyledonous seed germi-
Fic. 73.— Tur nates, five bundles are usually formed in
SCATTERED
BUNDLES OR :
SrRanps, in interposed
monocotyledons between
at a, and the bun-
dies ina circle in them, and
dicotyledons at 4. the multi-
plication continues, in
tough plants, until the
bundles touch (Fig. 74,
right). The inner parts
thus form a ring of wood
and the outer parts form
the inner bark orbast. A
new ring of wood or bast
is formed on stems of di-
cotyledons each year, and
the age of a cut stem is
easily determined.
When cross-sections of
monocotyledonous and di-
cotyledonous bundles are
examined under the mi-
croscope, it is readily seen
its hypocotyl (Fig. 74); soon five more are
FIG. 75.— FIBRO-VASCULAR BUNDLE OF
INDIAN CORN, much magnified.
A, annular vessel; A’, annular or spiral vessel ;
TT", thick-walled vessels; W, tracheids or
woody tissue; /, sheath of fibrous tissue sur-
rounding the bundle; 7, fundamental tissue
or pith; S, sieve tissue; P, sieve plate; C,
companion cell; /, intercellular space, formed
by tearing down of adjacent cells; W’, wood
parenchyma.
THE STEM—ITS GENERAL STRUCTURE 63
why dicotyledonous bundles form rings of wood and mono-
cotyledonous cannot (Figs. 75 and 76). The dicotyledon-
ous bundle (Fig. 76) has, running across it, a layer of brick-
shaped cells called cambium, which cells are a specialized
form of the parenchyma cells and retain the power of
FIG. 76. — THE DICOTYLEDONOUS BUNDLE OR WOOD STRAND. Upper figure
is of moonseed :
¢c,cambium; d, ducts; 1, end of first year’s growth; 2, end of second year’s growth ; bast
part at left and wood part at right. Lower figure (from Wettstein) is sunflower: 4, wood-
cells; g, vessels; c,cambium; Z, fundamental tissue or parenchyma; 4, bast; 6%, bast
parenchyma; s, sieve-tubes.
growing and multiplying. The bundles containing cam-
bium are called open bundles. There is no cambium in
monocotyledonous bundles (Fig. 75) and the bundles are
called closed bundles. Monocotyledonous stems soon cease
to grow in diameter. The stem of a palm tree is almost
64 BEGINNERS’ BOTANY
as large at the top as at the base. As dicotyledonous
plants grow, the stems become thicker each year, for the
delicate active cambium layer forms new cells from early
spring until midsummer or autumn, adding to the wood
within and to the bark without. As the growth in spring
is very rapid, the first wood-cells formed are much larger
than the last wood-cells formed by the slow growth of the
FIG. 77.— WHITE PINE STEM, 5 years old. The outermost layer is bark.
late season, and the spring wood is less dense and of a
lighter cclour than the summer wood; hence the time
between two years’ growth is readily made out (Figs. 77
and 78). Because of the rapid growth of the cambium in
spring and its consequent soft walls and fluid contents, the
bark of trees ‘‘peels’’ readily at that season.
Medullary Rays.— The first year’s growth in dicotyle-
dons forms a woody ring which almost incloses the pith,
and this is left as a small cylinder which does not grow
THE STEM—ITS GENERAL STRUCTURE 65
larger, even if; the’ tree should live’a icentury.. It sis’ not
quite inclosed, however, for the narrow layers of soft cells
separating the bundles remain be-
tween them (Fig. 78), forming ra-
diating lines called medullary rays
or pith rays.
The Several Plant Cells and their
Functions,— In the wood there are
some parenchyma cells that have
thin walls still, but have lost
the power of di-
vision. They are
now storage cells. FIG. 78. — ARRANGEMENT OF
TISSUES IN ‘TWO-YEAR-
There are also op Stem oF MoonsEED.
wood fibres which 4, pith; 4 parenchyma. The fibro-
are thick-walled vascular bundles, or wood
strands, are very prominent, with
FIG. 79.— MARKINGS and rigid (h, Fig. thin medullary rays between.
IN CELL WALLS
or Woop Fisre (6), and serve to support the sap-canals
) spiral: an annular, OF. WO0d Vessels’ (or, tracheids) ‘that. are
sey sealaniorn: formed by the absorption of the end
walls of upright rows of cells; the canals
pass from the roots to the twigs and even
to ribs of the leaves and serve to transport
the root water. They are recognized (Fig.
79) by the peculiar thickening of the wall
on the inner surface of the tubes, occur-
ring in the form of spirals. Sometimes the
whole wall is thickened except in spots
called gzts (.¢, Fig. 76). These thin spots
(Fig. 80) allow the sap to pass to other 4, 9.—prrs in
cells or to neighbouring vessels. THE CELL WALL.
The cambium, as we have seen, consists Longitudinal section of
wall at 4, showing
of cells whose function is growth. These _ pitborders ato, 0.
F
66 BEGINNERS’ BOTANY
cells are thin-walled and filled with protoplasm. During
the growing season they are continually adding to the
wood within and the bark with-
out; hence the layer moves out-
ward as it deposits the new
woody layer within.
The bark consists of inner or
fibrous bark or new bast (these
fibres in flax become linen), the
green or middle bark which func-
tions somewhat as the leaves,
and the corky or outer bark.
The common word “bark” is
seen, therefore, not to represent
a homogeneous or simple struc-
ture, but rather a collection of
FIG. 8r.— SIEVE-TUBES, 5, 5;
several kinds of tissue, all sepa-
pf shows a top view of a sieve-plate, ;
with’ afcompanion celll aeanthes, Taune (trom sthe. wooumbenearm
nies gions Sremines © by means of cambium, The new
plasm is shrunken from the walls bast contains (1) the szeve-tubes
cibina ae (Fig. 81) which transport the
sap containing organic substances, as sugar
and proteids, from the leaves to the parts
needing it (s, Fig. 76). These tubes have
been formed like the wood vessels, but
they have sieve-plates to allow the dense
organic-laden sap to pass with sufficient
readiness for purposes of rapid distribu-
tion. (2) There are also thick-walled dast
fibres (Fig. 82) in the bast that serve
for support. (3) There is also some MU
parenchyma in the new bast; it is FIG. 82—THICK-
WALLED BasT
now in part a stcrage tissue, Some- Grits
THE STEM—ITS GENERAL STRUCTURE 67
times the walls of parenchyma cells in the cortex thicken
at the corners and form érace cells (Fig. 83) (collenchyma)
for support, sometimes the whole wall is thickened, form-
ing grit cells or stone cells (Fig.
84; examples in
tough parts of
pear, or in stone
of fruits). Some
parts serve for
Fic. 83.— CoLien- Secretions (milk,
CHYMA IN WILD yosin, etc.) and
JEWELWEED OR
‘TOUCH-ME-NOT (IM-
PATIENS). tubes.
The outer bark of old shoots consists of covky cells that
protect from mechanical injury, and that contain a fatty sub-
stance (suberin) impermeable to water and of service to
kecp in moisture. There is sometimes a cork cambium (or
phellogen) in the bark that serves to extend the bark and
are called latex
FIG. 84. — GRIT CELLS,
keep it from splitting, thus increasing its power to protect.
Transport of the ‘‘ Sap.’?—We shall soon learn that the
common word “sap” does not represent a single or simple
substance. We may roughly distinguish two kinds of more
or less fluid contents: (1) ce voot water, sometimes called
mineral sap, that is taken in by the root, containing its
freight of such inorganic substances as potassium, calcium,
iron, and the rest; this root water rises, we have found, zz
the wood vessels, —that is, in the young or “sapwood” (p.
96); (2) the elaborated or organized materials passing back
and forth, especially from the leaves, to build up tissues
in all parts of the plant, some of it going down to the roots
and root-hairs; this organic material is transported, as we
have learned, 22 the steve-tubes of the inner bast, — that is,
in the “inner bark.” Removing the bark from a trunk in
68 BEGINNERS’ BOTANY
a girdle will not stop the upward rise of the root water so
long as the wood remains alive; but it will stop the passage
of the elaborated or food-stored materials to parts below
and thus starve those parts; and if the girdle does not
heal over by the deposit of new bark, the tree will in time
starve to death, It will now be seen that the common
practice of placing wires or hoops about trees to hold
them in position or to prevent branches from falling is
irrational, because such wires interpose barriers over which
the fluids cannot pass; in
time, as the trunk increases
in diameter, the wire girdles
the tree. It is much better
to bolt the parts together by
rods extending through the
branches (Fig. 85). These
bolts should fit very tight in
their holes. Why?
Wood.— The main stem
{s ? \ /\ any
NY,
\
pi
: or trunk, and sometimes
Fic. 85.—THE WRONG WAY TO
Sy Gi Ge Coen | NE larger branches, are the
sources of lumber and tim-
ber. Different kinds of wood have value for their special
qualities. The business of raising wood, for all purposes,
is known as forestry. The forest is to be considered as a
crop, and the crop must be harvested, as much as corn or
rice is harvested. Man is often able to grow a more pro-
ductive forest than nature does.
Resistance to decay gives value to wood used for shingles
(cypress, heart of yellow pine) and for fence posts (szd-
berry, cedar, post oak, bots a@arc, mesquite).
Hardness and. strength are qualities of great value in
building. Live oak is used in ships. Red oak, rock maple,
THE STEM—ITS GENERAL STRUCTURE 69
and yellow pine are used for floors. The best flooring is
sawn with the straight edges of the annual rings upward;
tangential sawn flooring may splinter. Chestnut is common
in some parts of the country, being used for ceiling and
inexpensive finishing and furniture. Locust and bors dare
(osage orange) are used for hubs of wheels; bois d’arc
makes a remarkably durable pavement for streets. /dony
is a tropical wood used for flutes, black piano keys, and
fancy articles. Ash is straight and elastic; it is used
for handles for light implements. A7zckory is very strong
as well as elastic, and is superior to ash for handles, spokes,
and other uses where strength is wanted. Hickory is
never sawn into Jumber, but is split or turned. The
“second growth,” which sprouts from stumps, is most
useful, as it splits readily. Fast-growing hickory in rich
land is most valuable. The supply of useful hickory is
being rapidly exhausted.
Softness zs often important. White pine and sweet gum
because of their softness and lightness are useful in box-
}
making. “Georgia” or southern pine is harder and stronger
than white pine; it is much used for floors, ceilings, and
some kinds of cabinet work. White pine is used for window-
sash, doors, and moulding, and cheaper grades are used for
flooring. Hemlock is the prevailing lumber in the east for
the framework and clapboarding of buildings. Redwood
and Douglas spruce are common building materials on the
Pacific coast. Cypress is soft and resists decay and is
superior to white pine for sash, doors, and posts on the
outside of houses. Cedar is readily carved and has a
unique use in the making of chests for clothes, aS its odour
repels moths and other insects. W2z//ow is useful for bas-
kets and light furniture. Passzwood or linden is used for
light ceiling and sometimes for cheap floors. Whitewood
7O BEGINNERS’ BOTANY
(incorrectly called poplar) is employed for wagon bodies
and often for house finishing. It often resembles curly
maple.
Beauty of grain and polish gives wood value for furni-
ture; pianos, and the like. Jahogany and white oak are
most beautiful, although red oak is also used. Oak logs
which are first quartered and then sawn radially expose the’
beautiful silver grain (medullary rays). Fig. 86 shows one
mode of quartering.
The log is quartered
on the lines a, a, 6,0;
then succeeding
boards are cut from
each quarter at I,
“Hae es
Say ® 2 3ete. Thencarer
t\ be ),
WAS AS eee the heart the better
“ OO) 5 ?
AS SS Se Wii bd the pen why?
SS Saar gaas Ordinary boards are
SS See sawn tangentially,
SE PEP as c,c. Curly pine,
b Jegone
curly walnut, and
FIG. 86.— THE MAKING CF ORDINARY BOARDS, i Sp
Ki = G
AND ONE WAY OF MAKING “ QUARTERED” bird's CHET ple are
BOARDS. woods that owe their
beauty of grain to wavy lines or buried knots. A mere
stump of curly walnut is worth several hundred dollars.
Such wood is sliced very thin for veneering and glued
over other woods in making pianos and furniture. If
the cause of wavy grain could be found out and such wood
grown at will, the discovery would be very useful. JZaf/e is
much used for furniture. Birch may be coloured so as very
closely to represent mahogany, and it is useful for desks.
Special Products cf Trees.—Cor:: from the bark of the
cork oak in Spain, latex from the rubber, and sap from the
THE STEM—ITS GENERAL STRUCTURE 7%
sugar-maple trees, turpentine from pine, tannin from oak
bark, Peruvian bark from cinchona, are all useful products.
Succestions. — Parts of a rootand stem through which liquids
vise. 49. Pull up a small plant with abundant leaves, cut off the
root so as to leave two inches or more on the plant (or cut a leafy
shoot of squash or other strong-growing coarse plant), and stand it
in a bottle with a little water at the bottom which has been coloured
with red ink (eosine). After three hours examine the root; make
cross sections at several places. Has the water coloured the axis
cylinder? ‘The cortex? What is your conclusion? Stand some
cut flowers or a leafy plant with cut stem in the same solution and
examine as before: conclusion? 50. Girdle a twig of a rapidly
growing bush (as willow) in early spring when growth begins (a)
by very carefully removing only the bark, and (4) by cutting away
also the sapwood. Under which condition do the leaves wilt ?
Why? 51. Stand twigs of willow in water; after roots have formed
under the water, girdle the twig (in the two ways) above the roots.
What happens to the roots, and why? 52. Observe the swellings
on trees that have been girdled or very badly injured by wires or
otherwise: where are these swellings, and why? 53. Kinds of
wood. Let each pupil determine the kind of wood in the desk,
the floor, the door and window casings, the doors themselves, the
sash, the shingles, the fence, and in the small implements and
furniture in the room; also what is the cheapest and the most
expensive lumber in the community. 54. How many kinds of
wood does the pupil know, and what are their chief uses?
Nore To TEAcHER. — The work in this chapter is intended to be
mainly descriptive, for the purpose of giving the pupil a rational
conception of the main vital processes associated with the stem,
in such a way that he may translate it into his daily thought. It
is not intended to give advice for the use of the compound micro-
scope. If the pupil is led to make a careful study of the text, draw-
ings, and photographs on the preceding and the following pages,
he will obtain some of the benefit of studying microscope sections
without being forced to spend time in mastering microscope
technique. If the school is equipped with compound microscopes,
a teacher is probably chosen who has the necessary skill to
manipulate them and the knowledge of anatomy and physiology
that goes naturally with such work; and it would be useless to
give instruction in such work in a text of this kind. The writer is
of the opinion that the introduction of the compound microscope
into first courses in botany has been productive of harm. Good
and vital teaching demands first that the pupil have a normal,
72 BEGINNERS’ BOTANY
direct, and natural relation to his subject, as he commonly meets
it, that the obvious and significant features of the plant world be
explained to him and be made a means of training him. ‘The
beginning pupil cannot be expected to know the fundamental
physiological processes, nor is it necessary that these processes
should be known in order to have a point of view and trained
intelligence on the things that one customarily sees. Many a
pupil has had a so-called laboratory course in botany without
having arrived at any real conception of what plants mean, or
without having had his mind opened to any real sympathetic
touch with his environment. Even if one’s knowledge be not
deep or extensive, it may still be accurate as far as it goes, and
his outlook on the subject may be rational.
Fic. 87. — THE MANY-STEMMED THICKETS OF MANGROVE OF SOUTHERN-
MOST SEACOASTS, many of the trunks being formed of aérial roots,
CHAPTER) Xt
LEAVES —FORM AND POSITION
LEAVES may be studied from four points of view, — with
reference to (1) their /inds and shapes; (2) their poszdzon, or
arrangement on the plant; (3) their avzatomy, or structure ;
3:
Oo
s
BSS
T
ae
FIG. 88.— A SIMPLE NETTED-VEINED LEAF.
(4) their function, or the work they
perform. This chapter is concerned
with the first @ two categories.
FIG. 89.—A SIMPLE PAR-
ALLEL-VEINED LEAF.
Kinds. —- Leaves
are simple or un-
branched (Figs. 88,
89), and compound or
FIG, 90.— COMPOUND OR BRANCHED LEAF
OF BRAKE (a common fern). branched (Fig. 90).
73
74 BEGINNERS? BOTANY
The method of compounding or branching follows the
mode of veining. The veining, or venation, is of two gen-
eral kinds. In some plants the main veins
diverge, and there is a conspicuous net-
work of smaller veins; such leaves are
netted-veined. They are characteristic of
the dicotyledons. In other plants the
main veins are parallel, or nearly so, and
there is no conspicuous network; these
are parallel-veined leaves (Figs. 89, 102).
These leaves are the rule in monocoty-
ledonous plants. The venation of netted-
veined leaves is pinnate or feather-like
on micor when the veins arise from the side of a
PLETE LEAVES OF continuous midrib (Fig. 91); palmate or
ere digitate (hand-like) when the veins arise |
from the apex of the petiole (Figs. 88, 92). If leaves were
divided between the main veins, the former would be
pinnately and the latter digitately compound.
It is customary to speak of a leaf as compound only
when the parts or branches are completely separate blades,
FIG. 92. — DIGITATE-VEINED PEL- FIG. 93. — PINNATELY COMPOUND
TATE LEAF OF NASTURTIUM. LEAF OF ASH.
as when the division extends to the midrib (Figs. 90, 93,
94,95). The parts or branches are known as leaflets.
LEAVES— FORM AND POSITION 75
Sometimes the leaflets themselves are compound, and the
whole leaf is then said to be bi-compound or twice-com-
FIG. 94.— DIGI-
TATELY COMPOUND
LEAF OF RASP-
BERRY.
FIG. 95.— POISON Ivy. LEAF AND FRUIT.
pound (Fig. 90). Some leaves are three-compound, four-
compound, or five-compound. Decompound is a general
term to .expressany degree of
compounding beyond twice-com-
pound.
Leaves that are not divided as
far as to the midrib are said to
be:
lobed, if the openings or sinuses
are not more than half the depth
of the blade (Fig. 96);
cleft, if the sinuses are deeper
FIG. 96. — LOBED LEAF OF
than the middle; SUGAR MAPLE,
76 BEGINNERS’ BOTANY
parted, if the sinuses
reach two thirds or more
to the midrib (Fig. 97);
divided, if the sinuses
reach nearly or quite to
the midrib.
The parts are called
lobes, divisions, or seg-
ments, rather than leaf-
Fic. 97.—DiciTaTeLy Partep Leaves lets. The leaf may be
Qe SCONES, pinnately or digitately
lobed, parted, cleft, or divided. A pinnately parted or
cleft leaf is sometimes said to be pinnatifid.
Leaves may have
one or all of three
parts — blade, or
expanded part; pe-
tiole, or stalk ; stip-
ules, or “TA
~S SIN
5 SRN NS
appendages Seas
at the base of the ~
petiole. A leaf that
hasallthreeof these
parts is said to be
complete (Figs. 91, aS,
106). The stipules
are often green and
leaflike and per-
form the function Fic. 98.—Ostonc- \ ovaTE SESSILE LEAVES OF
of foliage as in the Tee
pea and the Japanese quince (the latter common in yards).
Leaves and leaflets that have no stalks are said to be
sessile (Figs. 98, 103), z.¢. sitting. Find several examples.
LEAVES— FORM AND POSITION a7
The same is said of flowers and fruits.
The blade of a sessile leaf may partly or
_ wholly surround the stem, when it is said
to be clasping. Examples: aster (Fig. 99),
corn. In some cases the leaf runs down
the stem, forming.a wing; such leaves are
said to be decurrent (Fig. 100). When i
opposite sessile leaves are joined by their Fic, 99.— Crasp-
bases, they are said to be connate (Fig. 101). ING Tees
WILD ASTER.
Leaflets may have one or all of these
three parts, but the stalks of
leaflets are called petiolules
and the stipules of leaflets are
called stipels. The leaf of the
garden bean has leaflets, peti-
Hig» 2002. DE ‘olules; atid:stipels.
CURRENT
LEAVES OF The blade is usually attached
MULLEIN. to the petiole by z¢s lower edge.
In pinnate-veined leaves, the petiole seems to
continue through the leaf as a midrib (Fig. 91).
In some plants, however, the petiole joins
the blade inside or beyond the margin (Fig. 92). Such
leaves are said to be pel-
tate or shield-shaped. This
mode of attachment is par-
ticularly common in float-
ing leaves (e.g. the water
lilies). Peltate leaves are
usually digitate-veined.
How to Tell a Leaf. —It
is often difficult to distin-
guishcompound leaves from
FIG. to1.— TWO PAIRS OF CONNATE
leafy branches, and leaflets LEAVES OF HONEYSUCKLE.
78 BEGINNERS’ BOTANY
from leaves. As a rule leaves can be distinguished by
the following tests: (1) Leaves are temporary structures,
sooner or later falling. (2) Usually duds are borne in their
axils. (3) Leaves are usually dorne at joints or
nodes. (4) They arise on wood of the current
years growth. (5) They have a more or less
definite arrangement. When leaves fall, the twig
that bore them remains; when leaflets fall, the
main petiole or stalk that bore them also falls.
Shapes. — Leaves and leaflets are infinitely
variable in shape. Names have been given to
some of the more definite or regular shapes.
These names are a part of the language of bot-
any. The names represent ideal or
typical shapes; there are no two
leaves alike and very
few that perfectly con-
form to the definitions. i
The shapes are likened
to those of familiar ob- T pe
MES
jects or of geometrical
FIG. 102. — figures. Some of the
LINEAR- commoner shapes are as
ACUMINATE
Lear or ‘follows (name original yy. 103. — SHORT-OBLONG
Grass. = examples in each class): LEAVES OF Box.
Linear, several times longer than broad, with the sides
nearly or quite parallel. Spruces and most grasses
are examples (Fig. 102). In linear leaves, the main
veins are usually parallel to the midrib.
Oblong, twice or thrice as long as broad, with the sides
parallel for most of their length. Fig. 103 shows the
\ short-oblong leaves of the box, a plant that is used
for permanent edgings in gardens.
LEAVES— FORM AND POSITION 79
Elliptic differs from the oblong in having the sides gradu-
ally tapering to either end from the middle. The
European beech (Fig. 104) has elliptic
leaves. (This tree is often planted in
this country. )
Lanceolate, four to six times longer than
broad, widest below the middle, and
tapering to either end. Some of the
narrow-leaved willows are examples.
Most of the willows and the peach
have oblong-lanceolate leaves.
F ELLIPTIC LEAF
Spatulate, a narrow leaf that is broadest Guaeieent
toward the apex. The top is usually BEECH,
q rounded.
FIG. 105. — OVATE
SERRATE LEAF OF
HIBISCUS.
Fic. 106.—LeEar or APPLe, showing blade,
petiole, and small narrow stipules.
Ovate, shaped somewhat like the longitudinal section of an
the base to the apex. This is one of the commonest
egg: about twice as long as broad, tapering from near
leaf forms (Figs. 105, 106).
So BEGINNERS’ BOTANY
Obovate, ovate inverted,— the wide part towards the apex.
Leaves of mullein and leaflets of horse-chestnut and
false indigo are obovate. This form is commonest
in leaflets of digitate leaves: why?
Reniform, kidney-shaped. This form is sometimes seen in
ap wild plants, particularly in root-leaves. Leaves of
wild ginger are nearly reniform.
Orbicular, circular in general outline. Very few leaves are
) perfectly circular, but there are many that are
nearer circular than of any other shape. (Fig. 107).
FIG. 107. —ORBICULAR FIG. 108. — TRUNCATE
LOBED LEAVES. LEAF OF TULIP TREE.
The shape of many leaves is described in combinations
of these terms: as ovate-lanceolate, lanceolate-oblong.
The shape of the base and the apex of the leaf or leaflet
is often characteristic. The base may be rounded (Fig.
104), tapering (Fig. 93), cordate or heart-shaped (Fig. 105),
truncate or squared as if cut off. The apex may be blunt
or obtuse, acute or sharp, acuminate or long-pointed, trun-
cate (Fig. 108). Name examples.
The shape of the margin is also characteristic of each
kind of leaf. The margin is entire when it is not in-
dented or cut in any way (Figs. 99, 103). When not
LEAVES—FORM AND POSITION 81
entire, it may be undulate or wavy (Fig. 92), serrate or
saw-toothed (Fig. 105), dentate or more coarsely notched
(Fig. 95), crenate or round-toothed, lobed, and the like.
Give examples.
Leaves on the same plant often differ greatly in form.
Observe the different shapes of leaves on the young
zrowths of mulberries (Fig. 2) and wild grapes; also
on vigorous squash and pumpkin vines. In some cases
there may be simple and
compound leaves on the
same plant. This is
marked in the so-called
Boston ivy or ampelop-
3is (Fig. 109),.a vine
that 1s used to cover
brick and stone build-
ings. Different degrees
of cempounding, even
in the same leaf, may
often be found in honey
locust. Remarkable dif- Fic, 109, —DirFERENT FORMS OF LEAVES
ferences in forms are FROM ONE PLANT OF AMPELOPSIS.
seen by comparing seed-leaves with mature leaves of any
plant (Fig. 30).
The Leaf and its Environment.— The form and shape
of the leaf often have direct relation to the place in which
the leaf grows. Floating leaves are usually expanded and
fiat, and the petiole varies in length with the depth of
the water. Submerged leaves are usually linear or thread-
“ike, or are cut into very narrow divisions: thereby
more surface is exposed, and possibly the leaves are less
injured by moving water. Compare the sizes of the leaves
on the ends of branches with those at the base of the
G
82 BEGINNERS* LOTANY
branches or in the interior of the tree top. In dense
foliage masses, the petioles of the lowermost or under-
most leaves ¢end to elongate —to push the leaf to the light.
On the approach of winter the leaf usually ceases. to
work, and dies. It may drop, when it is said to be decidu-
ous; or it may remain on the plant, when it is said to be
persistent. If persistent leaves remain green during the
winter, the plant is said to be evergreen. Give examples
in each class. Most leaves fall by breaking off at the |
lower end of the petiole with a d¢stinct joint or articula-
tion. There are many leaves, however, that wither and
hang on the plant until torn off by the wind; of such
are the leaves of grasses, sedges, lilies, orchids, and other
plants of the monocotyledons. Most leaves of this char-
acter are parallel-veined.
Leaves also die and fall from lack of light. Observe the
yellow and weak leaves in a dense tree top or in any
thicket. Why do the lower leaves die on house plants?
Note the carpet of needles under the pines. All ever-
greens shed their leaves after a time. Counting back from
the tip of a pine or spruce shoot, determine how many
years the leaves persist. In some spruces a few leaves
may be found on branches ten or more years old.
Arrangement of Leaves. — Most leaves have a regular
position or arrangement on the stem. This position or
direction is determined largely by exposure to sunlight. In
temperate climates they usually hang in such a way that
they receive the greatest amount of light. One leaf shades
another to the least possible degree. If the plant were
placed in a new position with reference to light, the leaves
would make an effort to turn their blades.
When leaves are opposite the pairs usually alternate.
That is, if one pair stands north and south, the next pair
LEAVES— FORM AND POSITION 83
stands east and west. See the box-elder shoot, on the
left in Fig. 110. One pair does not shade the pair beneath.
The leaves are in four vertical ranks.
There are several kinds of alternate arrangement. Inthe
elm shoot, in Fig. 110, the third bud is vertically above the
finst=i) cubis’ is\, true “no
matter which bud is taken
as the starting point.
Draw a thread around
the stem until the two
buds. are joined. Set a
pin at each bud. Ob-
serve that two buds are
passed (not counting the
last) and that the thread
makes one circuit of the
stem. Representing the
number of buds by a de-
nominator, and the num-
ber of circuits by a
numerator, we have the FIG. 110. — PHYLLOTAXY OF Box ELDER,
fraction 3, which expresses EIM, APPLE.
the part of the circle that les between any two buds.
That is, the buds are one half of 360 degrees apart, or
180 degrees. Looking endwise at the stem, the leaves
are seen to be 2-ranked. Note that in the apple shoot
(Fig. 110, right) the thread makes two circuits and five
buds are passed: (wo fifths represents the divergence
between the buds. The leaves are 5-ranked.
Every plant has tts own arrangement of leaves. For
opposite leaves, see maple, box elder, ash, lilac, honey-
suckle, mint, fuchsia. For 2-ranked arrangement, see
all grasses, Indian corn, basswood, elm. For 3-ranked
84 BEGINNERS’? BOTANY
arrangement, see all sedges. For 5-ranked (which is one
of the commonest), see apple, cherry, pear, peach, plum,
poplar, willow. For 8-ranked, see holly, osage orange,
some willows. More complicated arrangements occur in
bulbs, house leeks, and other condensed plants. The buds
or “eyes” on a potato tuber, which is an underground stem
(why ?), show a spiral arrangement (Fig. 111).
The arrangement of leaves on the stem ts
known as phyllotaxy (literally, “leaf arrange-
ment”). Make out the phyllotaxy on six
different plants nearest the schoolhouse door.
In some plants, several leaves occur at one
level, being arranged in a circle around the
stem. Such leaves are said to be verticillate,
or whorled. Leaves arranged in this way are
usually narrow: why? |
Although a definite arrangement of leaves
is the rule: in ‘most plants,“ wsssubpecrazo
. modification. On shoots that receive the
Fic. 11.— light only from one side or that grow in dif-
eee ficult positions, fhe arrangement may not be
Tato TuBER. definite. Examine shoots that grow on the
Work itout under side of dense tree tops or in other par-
on a fresh ; :
longtuber. tially lighted positions.
SuccEstions. — 55. The pupil should match leaves to determine
whether any two are alike. Why? Compare leaves from the
same plant in size, shape, colour, form of margin, length of petiole,
venation, texture (as to thickness or thinness), stage of maturity,
smoothness or hairiness. 56. Let the pupil take an average
leaf from each of the first ten different kinds of plants that
he meets and compare them as to the above points (in Exer-,
cise 55), and also name the shapes. Determine how the various
leaves resemble and differ. 57. Describe the stipules of rose,
apple, fig, willow, violet, pea, or others. 58. In what part of
the world are parallel-veined leaves the more common ? 59. Do
LEAVES— FORM AND POSITION 85
you know of parallel-veined leaves that have lobed or dentate mar-
gins? 60. What becomes of dead leaves? 61. Why is there
no grass or other undergrowth under pine and spruce trees ?
62. Name several leaves that are useful for decorations. Why
are they useful? 63. What trees in your vicinity are most
esteemed as shade trees ? What is the character of their foliage P
64. Why are the internodes so long in water-sprouts and suckers ?
65. How do foliage characters in corn or sorghum differ when the
plants are grown in rows or broadcast ? Why? 66. Why may
removal of half the plants increase the yield of cotton or sugar-
beets or lettuce ? 67. How do leaves curl when they wither ?
Do different leaves behave differently in this respect? 68. What
kinds of leaves do you know to be eaten by insects? By cattle?
By horses? What kinds are used for human food? 69. How
would you describe the shape of leaf of peach? apple? elm?
hackberry? maple? sweet-gum? corn? wheat? cotton? hickory?
cowpea? strawberry? chrysanthemum ? rose? carnation? 70. Are
any of the foregoing leaves compound? How do you describe the
shape of acompound leaf? 71. How many sizes of leaves do you
find on the bush or tree nearest the schoolroom door? 72. How
many colours or shades? 73. How many lengths of petioles?
74, Bring in all the shapes of leaves that you can find.
!
“ iQ
\ ub\y
lig Nein Ni
He ar Ses nN Aa
AN a SSE
PF \ Oe
FIG. 112. — Cow-
PEA. Describe
the leaves. For
what is the plant
used ?
CHAPTER XII
LEAVES —STRUCTURE OR ANATOMY
BesipEs the framework, or system of veins found in
blades of all leaves, there is a soft cellular tissue called
mesophyll, or leaf parenchyma, and an epidermis or skin
that covers the entire outside part.
Mesophyll.— The mesophyll is zot all alike or homoge-
neous. The upper layer is composed of elongated cells
placed perpendicular to the surface of the leaf. These
are called palisade cells. These cells are usually filled
with green bod-
ies called chlo-
rophyll grains.
The grain con-
tains a_ great
number of chlo-
& 5)
yee,
a © METAR) rophyll drops
heh AG Oh imbedded in
FIG, 113.— SECTION OF A LEAF, showing the air spaces. the protoplasm.
Breathing-pore or stoma ata. The palisade cells which chiely Below the pali-
contain the chlorophyll are at 6. Epidermal cells at c.
sade cells is the
spongy parenchyma, composed of cells more or less spher-
cal in shape, irregularly arranged, and provided with many
intercellular air cavities (Fig. 113). In leaves of some
plants exposed to strong light there may be more than one
layer of palisade cells, as in the India-rubber plant and
the oleander. Ivy when grown in bright light will develop
two such layers of cells, but in shaded places it may be
86
LEAVES— STRUCTURE OR ANATOMY 87
found with only one. Such plants as iris and compass
plant, which have both surfaces of the leaf equally exposed
to sunlight, usually have a palisade layer beneath each
epidermis.
Epidermis. —-The outer or epidermal cells of leaves do
not bear chlorophyll, but are usually so transparent that
the green mesophyll can be seen through them. They
often become very thick-walled, and are in most plants
devoid of all protoplasm except a thin layer lining the
walls, the cavities being filled with cell sap. This sap is
sometimes coloured, as in the under epidermis of begonia
leaves. It is not common to find more than one layer of
epidermal cells forming each surface of a leaf. The epi-
dermis serves to retain motsture in the leaf and as a general
protective covering. In desert plants the epidermis, as a
rule, is very thick and has a dense cuticle, thereby pre-
venting loss of water.
There are various outgrowths of the epidermis. Hairs
are the chief of these. They may be (1) simple, as on
primula, geranium, negelia; (2) once branched, as on wall-
flower; (3) compound, as on verbascum or mullein; (4)
disk-like, as on shepherdia; (5) stellate, or star-shaped, as
in certain crucifers. In some cases the hairs are glandular,
as in Chinese primrose of the greenhouses (Przmula
Sinensis) and certain hairs of pumpkin flowers. The hairs
often protect the breathing pores, or stomates, from dust
and water.
Stomates (sometimes called breathing-pores) ave small
openings or pores in the epidermis of leaves and soft stems
thet allow the passage of air and other gases and vapours
(stomate or stoma, singular; stomates or stomata, plural).
They are placed near the large intercellular spaces of the
mesophyll, usually in positions least affected by direct
88 BEGINNERS’ BOTANY
sunlight. Fig. 114 shows the structure. There are two
guard-cells at the mouth of each stomate, which may in
most cases open or close the passage as the conditions
of the atmosphere may require. The guard-cells contain
FIG. 114. — DIAGRAM OF STOMATE FIG. 115. —STOMATE OF Ivy,
OF IRIS (Osterhout). showing compound guard-cells.
chlorophyll. In Fig. 115 is shown a case in which there
are compound guard-cells, that of ivy. On the margins
of certain leaves, as of fuchsia, impatiens, cabbage, are
openings known as water-pores.
Stomates are very numerous, as will be seen from the num-
bers showing the pores to each square inch of leaf surface:
Lower surface Upper surface
CODY? sur etuine to hie gone, ate G7 OO None
Elly ct eer wemesely carewiiks | Keto aaks (SOOO None
Eta Cheeta epctete s30 Coen edness leat OOOO None
Mistletoe series onritit) atin ven won Setliens 200 200
Tradescanitiayer yas ale alee em ee Wie; OOO 2,000
Gardeni Flag (vis). *25..9.9 2 11,572
The arrangement of stomates on the leaf differs with
each kind of plant. Fig. 116 shows stomates and also the
outlines of contiguous epidermal cells.
The function or work of the stomates
is to regulate the passage of gases into
and out of the plant. The directly
active organs or parts are guard-cells,
on either side the opening. One
FIG. 116, — STOMATES 5: 5
OF GERANIUM Lear, method of opening is as follows: The
LEAVES— STRUCTURE OR ANATOMY 89
thicker walls of the guard-cells (Fig. 114) absorb water
from adjacent cells, these thick walls buckle or bend and
part from one another at their middles on either side the
opening, causing the stomate to open, when the air gases
may be taken in and the leaf gases may pass out. When
moisture is reduced in the leaf tissue, the guard-cells part
with some of their contents, the thick walls
straighten, and the faces of the two opposite
ones come together, thus closing the stomate
and preventing any water vapour from pass-
ing out. When a leaf is actively at work
making new organic compounds, the stomates
are usually open; when unfavourable condt-
tions arise, they are usually closed. They
also commonly close at night, when growth
(or the utilizing of the new materials) is most
likely to be active. It is sometimes safer to
fumigate greenhouses and window gardens
at night, for the noxious vapours are less
likely to enter the leaf. Dust may clog or
cover the stomates. Rains benefit plants
by washing the leaves as well as by provid-
ing moisture to the roots. FIG. 117. — LEN-
Lenticels. — On the young woody twigs Sane Tae
of many plants (marked in osiers, cherry, OF RED OsIER
birch) there are small corky spots or eleva- ee
tions known as lenticels (Fig. 117). They mark the loca-
tion of some loose cork cells that function as stomates,
for green shoots, as well as leaves, take in and discharge
gases; that is, soft green twigs function as leaves. Under
some of these twig stomates, corky material may form
and the opening is torn and enlarged: ¢he Jlenticels are
successors to the stomates. The stomates lie in the epi-
Lote) BEGINNERS’ BOTANY
dermis, but as the twig ages the epidermis perishes and
the bark becomes the external layer. Gases continue to
pass in and out through the lenticels, until the branch be-
comes heavily covered with thick, corky bark. With the
growth of the twig, the lenticel scars enlarge lengthwise
or crosswise or assume other shapes, often becoming char-
acteristic markings.
Fibro-vascular Bundles. — We have studied the fibro-
vascular bundles of stems (Chap. X). These stem bun-
dles continue into the leaves, ramifying into the veins,
carrying the soil water inwards and bringing, by diffusion,
the elaborated food out through the sieve-cells. Cut
across a petiole and notice the hard spots or areas in it;
strip these parts lengthwise of the petiole. What are they?
Fall of the Leaf. —In most common deciduous plants,
when the season’s work for the leaf is ended, the nutritious
matter may be withdrawn, and a /ayer of corky cells ts com-
pleted over the surface of the stem where the leaf ts attached.
The leaf soon falls. It often falls even before it is killed
by frost. Deciduous leaves begin to show the surface line
of articulation in the early growing season. This articula-
tion may be observed at any time during the summer. The
area of the twig once covered by the petioles is called the
leaf-scar after the leaf has fallen. In Chap. XV are shown
a number of leaf-scars. In the plane tree (sycamore or
buttonwood), the leaf-scar is in the form of a ring surround-
ing the bud, for the bud is covered by the hollowed end of
the petiole; the leaf of sumac is similar. Examine with a
hand lens leaf-scars of several woody plants. Note the
number cf bundle-scars in each leaf-scar. Sections may
be cut through a leaf-scar and examined with the micro-
scope. Note the character of cells that cover the leaf-
scar surface.
LEAVES—STRUCTURE OR ANATOMY Ol
Succestions. — Zo study epidermal hairs: 75. For this study,
use the leaves of any hairy or woolly plant. A good hand lens will
reveal the identity of many of the coarser hairs. A dissecting micro-
scope will show them still better. For the study of the cell structure,
a compound microscope is necessary. Cross-sections may be made
so as to bring hairs on the edge of the sections; or in some
cases the hairs may be peeled or scraped from the epidermis and
placed in water ona slide. Make sketches of the different kinds of
hairs. 76. It is good practice for the pupil to describe leaves in
respect to their covering: Are they smooth on both surfaces? Or
hairy? Woolly? Thickly or thinly hairy? Hairs long or short?
Standing straight out or lying close to the surface of the leaf ?
Simple or branched? Attached to the veins or to the plane surface?
Colour? Most abundant on young leaves or old? 77. Place a
hairy or woolly leaf under water. Does the hairy surface appear
silvery? Why? Other questions: 78. Why is it good practice
to wash the leaves of house plants? 79. Describe the leaf-scars
on six kinds of plants: size, shape, colour, position with reference
to the bud, bundle-scars. 80. Do you find leaf-scars on mono-
cotyledonous plants—corn, cereal grains, lilies, canna, banana,
palm, bamboo, green brier? 81. Note the table on page 88.
Can you suggest a reason why there are equal numbers of stomates
on both surfaces of leaves of tradescantia and flag, and none on
upper surface of other leaves? Suppose you pick a leaf of lilac
(or some larger leaf), seal the petiole with wax and then rub
the under surface with vaseline ; on another leaf apply the vaseline
to the upper surface ; which leaf withers first, and why? Make a
similar experiment with iris or blue flag. 82. Why do leaves and
shoots of house plants turn towards the light? What happens
when the plants are turned around? 83. Note position of leaves
of beans, clover, oxalis, alfalfa, locust, at night.
CHAPTER XIII
LEAVES — FUNCTION OR WORK
WE have discussed (in Chap. VIII) the work or function
of roots and also (in Chap. X) the function of stems.
We are now ready to complete the view of the main vital
activities of plants by considering the function of the
green parts (leaves and young shoots).
Sources of Food. — The ordinary green plant has but zo
sources from which to secure food,— the air and the soil.
When a plant is thoroughly dried in an oven, the water
passes off ; ti7s water came from the soil. The remaining
part is called the dry substance or dry matter. If the dry
matter is burned in an ordinary fire, only the ash remains;
this ash came from the soil. The part that passed off as
gas in the burning contained the elements that came from
the air, it also contained some of those that came from
the soil —all those (as nitrogen, hydrogen, chlorine) that
are transformed into gases by the heat of a common fire.
The part that comes from the soil (the ash) is small in ©
amount, being considerably less than 10 per cent and
sometimes less than 1 per cent. Water is the most
abundant single constituent or substance of plants. Ina
corn plant of the roasting-ear stage, about 80 per cent of
the substance is water. A fresh turnip is over 90 per
cent water. Fresh wood of the apple tree contains about
45 per cent of water.
Carbon. — Carbon enters abundantly into the composition
of all plants. Note what happens when a plant is burned
92
LEAVES— FUNCTION OR WORK 93
without free access of air, or smothered, as in a charcoal
pit. A mass of charcoal remains, almost as large as the
body of the plant. Charcoal is almost pure caréon, the ash
present being so smali in proportion to the large amount
of carbon that we look on the ash as an impurity. Nearly
half of the dry substance of a tree is carbon. Carbon
goes off as a gas when the plant is burned iu air. It does
not go off alone, but in combination with oxygen in the
form of carbon dioxide gas, CO,.
The green plant secures its carbon from the air. In
other words, much of the solid matter of the plant comes
from one of the gases of the air. By volume, carbon dioxide
forms only a small fraction of 1 per cent. of the ar.
It would be very disastrous to animal life, however, if this
percentage were much increased, for it excludes the life-
giving oxygen. Carbon dioxide is often called ‘‘foul gas.”’
_Tt may accumulate in old wells, and an experienced person
will not descend into such wells until they have been tested
with a torch. If the air in the well will not support com-
bustion,—that is, if the torch is extinguished,—it usually
means that.carbon dioxide has drained into the place. The
air of a closed schoolroom often contains far too much of
this gas, along with little solid particles of waste matters.
Carbon dioxide is often known as carbonic acid gas.
Appropriation of the Carbon.—The carbon dioxide of the
air readily diffuses itself into the leaves and other green
parts of the plant. The leaf is delicate in texture, and when
very young the air can diffuse directly into the tissues.
The stomates, however, are the special inlets adapted for
the admission of gases into the leaves and other green
parts. Through these stomates, or diffusion-pores, the out-
side air enters into the air-spaces of the plant, and is finally
absorbed by the little cells containing the living matter.
94 BEGINNERS’.BOTANY
Chloronyll (‘‘leaf green’’) is the agent that secures
the energy by means of which carbon dioxide is utilized.
This material is contained in the leaf cells in the form of
grains (p. 86) ; the grains themselves are protoplasm, only
the colouring matter being chlorophyll. The chlorophyll
bodies or grains are often most abundant near the upper
surface of the leaf, where they can secure the greatest
amount. of light. Without this green colouring matter,
there would be no reason for the large flat surfaces which
the leaves possess, and no reason for the fact that the
leaves are borne most abundantly at the ends of branches,
where the light is most available. Plants with coloured
leaves as coleus, have chlorophyll, but it is masked by
other colouring matter. This other colouring matter is
usually soluble in hot water: boil a coleus leaf and notice
that it becomes green and the water becomes coloured.
Plants grown in darkness are yellow and slender, and
do not reach maturity. Compare the potato sprouts that
have grown from a tuber lying in a dark cellar with
those that have grown normally in the bright light.
The shoots have become slender, and are devoid of chloro-
phyll; and when the food that is stored in the tuber is
exhausted these shoots will have lived useless lives. A
plant that has been grown in darkness from, the seed will
soon die, although for a time the little seedling will grow
very tall and slender. Why? Light favours the production
of chlorophyll, and the chlorophyll is the agent in the mak-
ing of the organic carbon compounds. Sometimes chloro-
phyll is found in buds and seeds, but in most cases these
places are not perfectly dark. Notice how potato tubers de-
velop chlorophyll, or become green, when exposed to light.
Photosynthesis —Carbon dioxide diffuses into the leaf;
during sunlight it is used, and oxygen is given of. How
LEAVES—FUNCTION OK WORK 95
the carbon dioxide which is thus absorbed may be used in
making an organic food is a complex question, and need not
be studied here; but it may be stated that carbon dioxide
and water are the constituents. Complex compounds are
built up out of simpler ones.
Chlorophyll absorbs certain light rays, and the energy
thus directly or indirectly obtained is used by the living
matter in uniting the carbon dioxide absorbed from the air
with some of the water brought up from the roots. The
ultimate result usually is starch. The process is obscure,
but sugar is generally one step; and our first definite
knowledge of the product begins when starch is deposited
in the leaves. The process of using the carbon dioxide of
the air has been known as carbon assimilation, but the
term now most used is photosynthesis (from two Greek
words meaning light and placing together.)
Starch and Sugar.—All starch is composed of carbon,
hydrogen, and oxygen (C,H,,0;)n. The sugars and the
substance of cell walls are very similar to it in composition.
All these substances are called carbohydrates. In making
fruit sugar from the carbon and oxygen of carbon dioxide
and from the hydrogen and oxygen of the water, there
is a surplus of oxygen (6 parts CO, + 6 parts H.O
— C,H,,0, + 6 O,). It is this oxygen that-is given off
into the air during sunlight.
Digestion.—Starch is in the form of insoluble granules.
When such food material is carried from one part of the
plant to another for purposes of growth or storage, it is
made soluble before it can be transported. When this
starchy material is transferred from place to place, it is
usually changed into sugar by the action of a diastase.
This is a process of digestion. It is much lke the change
of starchy foodstuffs to sugary foods effected by the saliva.
96 BEGINNERS’ BOTANY
Distribution of the Digested Food. — After being changed
to the soluble form, ¢#zs material is ready to be used in
growth, either in the leaf, in the stem, or in the roots.
With other more complex products it is then dvstriduted
throughout all the growing parts
of the plant; and when passing
down to the root, it seems to pass
more readily through the zuzzer
dark, in plants which have a defi-
nite bark. This gradual down-
ward diffusion through the inner
bark of materials suitable for
growth is the process referred to
when the “descent of sap”’ is men-
tioned. Starch and other products
are often stored in one growing
season to be used in the next sea-
son. lf) axtree is constricted gor
FIG. 118.—TRUNK GirpLED strangled by a wire around its
By a Wines “See 8-5" trunk (Fig. 118), the digested food
cannot readily pass down and it is stored above the girdle,
causing an enlargement.
Assimilation. — Zhe food from the air and that from the
soil unite in the living tissues. The “sap” that passes
upwards from the roots in the growing season is made up:
largely of the soil water and the salts which have been
absorbed in the diluted solutions (p. 67). This upward-
moving water is conducted largely through certain tubular
canals of the young wood. These cells are never continu-
ous tubes from root to leaf; but the water passes readily
from one cell or canal to another in its upward course.
The upward-moving water gradually passes to the grow-
ing parts, and everywhere in the living tissues, it is, of
LEAVES— FUNCTION OR WORK 97
course,in the most intimate contact with the soluble carbo-
hydrates and products of photosynthesis. In the build-
ing up or reconstructive and other processes it is therefore
available. We may properly conceive of certain of the
simpler organic molecules as passing through a series of
changes, gradually increasing in complexity. There will
be formed substances containing nitrogen in addition to
carbon, hydrogen, and oxygen. Others will contain also
sulphur and phosphorus, and the various processes may
be thought of as culminating in protoplasm. Pvotoplasm
zs the living matter in plants. It is in the cells, and is
usually semifluid. Starch is not living matter. The
complex process of building up the protoplasm is called
assimilation.
Respiration. — Plants necd oxygen for respiration, as
animals do. Ne have seen that plants need the carbon
dioxide of the air. To most plants the nitrogen of the air
is inert, and serves only to dilute the other elements; but
the oxygen is necessary for all life. We know that all
animals need this oxygen in order to breathe or respire.
In fact, they have become accustomed to it in just the
proportions found in the air; and this is now best for
them. When animals breathe the air once, they make it
foul, because they use some of the oxygen and give off
carbon dioxide. Likewise, a// living parts of the plant must
have a constant supply of oxygen. Roots also need it, for
they respire. Air goes in and out of the soil by diffusion,
and as the soil is heated and cooled, causing the air to
expand and contract.
The oxygen passes into the air-spaces and is absorbed
by the moist cell membranes. In the living cells it makes
possible the formation of simpler compounds by which
energy is released. This energy enables the plant to
H
98 BEGINNERS’ BOTANY
work and grow, and the final products of this action are
carbon dioxide and water. As a result of the use of this
oxygen by night and by day, plants give off carbon dioxide.
Plants respire; but since they are stationary, and more or
less inactive, they do not need so much oxygen as animals do,
and they do not give off so much carbon dioxide. A few
plants in a sleeping room need not disturb one more than a
family of mice. It should be noted, however, that germina-
ting seeds respire vigorously, hence they consume much oxy-
gen; and opening buds and flowers are likewise active.
Transpiration. — Much more water is absorbed by the
roots than is used in growth, and ¢his surplus water passes
Jrom the leaves into the atmosphere by an evaporation process
known as transpiration. Transpiration takes place more
abundantly from the under surfaces of leaves, and through
the pores or stomates. A sunflower plant of the height
of a man, during an active period of growth, gives off a
quart of water per day. A large oak tree may transpire
150 gallons per day during the summer. For every ounce
of dry matter produced, it is estimated that 15 to 25 pounds
of water usually passes through the plant.
When the roots fail to supply to the plant sufficient water
to equalize that transpired by the leaves, the plant wilts.
Transpiration from the leaves and delicate shoots is in-
creased by all the conditions which increase evapora-
tion, such as higher temperature, dry air, or wind. The
stomata open and close, tending to regulate transpiration
as the varying conditions of the atmosphere affect the
moisture content of the plant. However, in periods of
drought or of very hot weather, and especially during a
hot wind, the closing of these stomates cannot sufficiently
prevent evaporation. The roots may be very active and
yet fail to absorb sufficient moisture to equalize that given
LEAVES— FUNCTION OR WORK 99
off by the leaves. The plant shows the effect (how ?).
On a hot dry day, note how the leaves of corn “roll”’ tow-
ards afternoon. Note how fresh and vigorous the same
leaves appear early the following morning. Any injury to
the roots, such as a bruise, or exposure to heat, drought, or
cold may cause the plant to wilt.
Water is forced up by root pressure or sap pressure.
(Exercise 99.) Some of the dew on the grass in the morn-
ing may be the water forced up by the roots; some of it is
the condensed vapour of the air.
The wilting of a plant ts due to the loss of water from
the cells. The cell walls are soft, and collapse. In Pig: 172, the
common wild clematis
A é FIG. 171. — LEAVES OF PEA,
or ‘old man vine,” this 4
— very large stipules, op-
mode is seen. posite leaflets, and leaflets
Meiners She entire represented by tendrils.
plant or shoot may wind about a support. Such a plant is
a twiner. Examples are bean, hop, morning-glory, moon-
flower, false bittersweet or waxwork (Ce/as¢rius), some
honeysuckles, wistaria, Dutchman’s pipe, dodder. The
free tip of the twining branch sweeps about in curves, much
as the tendril does, until it finds support or becomes old
and rigid.
Each kind of plant usually coils 2 only one direction.
Most plants coil against the sun, or from the observer’s
left across his front to his right as he faces the plant.
132 : BEGINNERS’ BOTANY
Examples are bean, morning-glory. The hop twines from
the observer’s right to his left, or with the sun.
FIG, 172. ~. CLEMATIS CLIMBING BY LEAF-TENDRIL.
SUGGESTIONS.—136. Set the pupil to watch the behaviour of any
plant that has tendrils at different stages of maturity. A vigorous
cucumber plant is one of the best. Just beyond the point of a young
straight tendril set a stake to compare the position of it. Note
whether the tendril changes position from hour to hour or day
to day. 137. Is the tip of the tendril perfectly straight? Why?
Set a small stake at the end of a strong straight tendril, so that the
tendril will just reach it. Watch and make drawing. 138. If a
tendril does not find a support what does it do? 139. To test the
movement of a free tendril draw an ink line lengthwise of it, and
note whether the line remains always on the concave side or the
convex side. 140. Name the tendril-bearing plants that you know.
141. Make similar observations and experiments on the tips of
twining stems. 142. What twining plants do you know, and which
way do they twine? 143. How does any plant that you know
shoot up? 144. Does the stem of a climving plant contain more
or less substance (weight) than an erect self-supporting stem of
the same height? Explain,
GHAPRTER. XVIIE
THE FLOWER—ITS PARTS AND FORMS
Tue function of the flower is to produce seed. It is
probable that all its varied forms and colours contribute
to this supreme end. These forms and colours please the
human fancy and add to the joy of living, but the flower
exists for the good of the plant, not for the good of man.
The parts of the flower are of two general kinds — those
that are directly concerned in the production of seeds, and
those that act as covering and protecting organs. The
former parts are known as the essential organs; the latter
as the floral envelopes.
Envelopes. — The floral envelopes usually bear a close
resemblance to leaves. These envelopes are very com-
monly of two series or kinds — the
outer and the zzner. The outer series,
known as the calyx, is usually smaller
and green. It usually comprises the
outer cover of the flower bud. The
calyx is the lowest whorl in Fig. 173.
FIG. 173.— FLOWER OF
The inner series, known as the A BUTTERCUP IN SEC-
TION.
corolla, is usually coloured and more
special or irregular in shape than the calyx. It is the
showy part of the flower, as a rule. The corolla is the
second or large whorl in Fig. 173.
The calyx may be composed of several leaves. Each
leaf is a sepal. If it is of one piece, it may be lobed or
divided, in which-case the divisions are called calyx-lobes.
133
134 BEGINNERS’ BOTANY
In like manner, the corolla may be composed of petals, or
it may be of one piece and variously lobed. A calyx of
one piece, no matter how deeply lobed, is gamosepalous. ~
A corolla of one piece is gamopetalous. When these
series are of separate pieces, as in Fig. 173, the flower is
said to be polysepalous and polypetalous. Sometimes both
series are of separate parts, and
sometimes only one of them is so
formed.
The floral envelopes are ho-
mologous with leaves. Sepals and
petals, at least when more than
three or five, are in more than
one whorl, and one whorl stands
below another so that the parts
overlap. They are borne on the
expanded or thickened end of the
flower stalk ; this end is the torus.
In Fig. 173 all the parts are seen
FIG. 174. — FLOWER OF as attached to the torus. This
FUCHSIA IN SECTION.
part is sometimes called the ve-
ceptacle, but this word is a common-language term of
several meanings, whereas torus has no other meaning.
Sometimes one part is attached to another part, as in the
fuchsia (Fig. 174), in which the petals are borne on the
calyx-tube.
Subtending Parts. — Sometimes there are /eaf-like parts
just below the calyx, \ooking like a second calyx. Such
parts accompany the carnation flower. These parts are
bracts (bracts are small specialized leaves); and they form
an involucre. We must be careful that we do not mistake
them for true flower parts. Sometimes the bracts are
large and petal-like, as in the great white blooms of the
THE FLOWER—ITS PARTS AND FORMS 135
flowering dogwood: here the real flowers are several,
small and greenish, forming a small cluster in the centre.
Essential Organs. — The essential organs are of two
series. The outer series is composed of the stamens. The
inner series is composed of the pistils.
Stamens bear the pollen, which is made up of grains or
spores, each spore usually being a single plant cell. The
stamen is of two parts, as is readily seen in Figs. 173,
174, the enlarged terminal part or anther, and the stalk
or filament. The filament is often so short as to seem to
be absent, and the anther is then said to be sessz/e. The
anther bears the pollen spores. It is made up of two or
four parts (known as sporangia or spore-cases), which
burst and discharge the
pollen. When the pollen is
shed, the stamen dies.
The pestil has. three
parts: the lowest, or seed-
bearing part, which is the
ovary; the stigma at the
upper extremity, which is
FIG. 175. — THE STRUCTURE OF A
a flattened or expanded PLUM BLossoM.
surface, and usually rougn- se, sepals; #, petals; sta, stamens; 0, ovary;
s, style; st, tigma. The pistil consists of
ened or sticky; the stalk- the ovary, the style and the stigma. It
contains the seed part. The stan:ens are
like part or style, connect- g;,5ed with anthers, in which the pollen is
ing the ovary and the stig- borne. The ovary, o, ripens into the fruit.
ma. Sometimes the style is apparently wanting, and the
stigma is said to be sessile on the ovary. These parts are
shown in the fuchsia (Fig. 174). The ovary or seed vessel
is at a. A long style, bearing a large stigma, projects from
the flower. See also Figs. 175 and 176.
Stamens and pistils probably are homologous with leaves.
A pistil is sometimes conceived to represent anciently a
136
BEGINNERS’ BOTANY
leaf as if rolled into a tube; and an anther, a leaf of which
the edges may have been turned in on the midrib.
FIG. 176. — SIMPLE
PISTILS OF BUT-
TERCUP, one in
longitudinal sec-
tion.
The pistil may be of one part or com-
partment, or of many parts. The different
units or parts of which it is composed are
carpels. Each carpel is homologous with
a leaf. Each carpel bears one or more
seeds. A pistil of one carpel is simple;
of two or more carpels, compound. Usu-
ally the structure of the pistil may be de-
termined by cutting horizontally across the lower or seed-
bearing part, as Figs. 177, 178 explain. A flower may
contain a simple pistil (one carpel), as
the pea (Fig. 177); several simple pis-
ti/s (several separate carpels), as the
buttercup (Fig. 176); or a compound
pistil with carpels united, as the Saint
John’s wort (Fig. 178) and apple. How
many carpels in an apple? A peach?
An okra pod? A bean pod? The
seed cavity in each carpel is called a
locule (Latin /ocus, a place). In these
locules the seeds are borne.
FIG.
GARDEN PEA, the
stamens being pulled
down in order to dis-
close it; also a section
177. — PISTIL OF
showing the
compartment
pare Fig. 188).
single
(com-
Fic. 178. —COMPOUND
PISTIE DS ORPWAT OE:
JOHN’S Wort.
has 5 carpels.
Conformation of the Flower.—A
flower that has calyx, corolla, stamens,
and pistils is said to be complete (Fig.
173); all others are incomplete. In
some flowers both the floral envelopes
are wanting: such are naked. When
one of the floral envelope series is
wanting, the remaining series is said
to be calyx, and the flower is therefore
apetalous (without petals). The knot-
It
THE FLOWER—ITS PARTS AND FORMS 137
weed (Fig. 179), smartweed, buckwheat, elm are
examples.
Some flowers lack the pistils: these are stami-
nate, whether the envelopes are missing or not.
Others lack the stamens: these are pistillate.
Others have neither stamens nor pistils: these
are sterile (snowball and hydrangea). Those
that have both stamens and pistils are per-
fect, whether or not the envelopes are missing.
Those that lack
eitherstamens or
pistils are imper-
fect or diclinous.
Staminate and
FIG. 179. — KNOTWEED, a very common but inconspicu- pistillate flowers
ous plant along hard walks and roads. Two flowers, '
enlarged, are shown at the right. These flowers are are imperfect or
very small and borne in the axils of the leaves. diclinous
When staminate and pistillate flowers are borne on the
same plant, ¢.g. oak (Fig. 180), corn,
beech, chestnut, hazel, walnut, hickory,
pine, begonia (Fig. 181), watermelon,
FIG. 181. — BEGONIA
FIG, 180.—STAMINATE CATKINS OF FLOWERS.
Oak. The pistillate flowers are in the Staminate at 4; pistil- |
leaf axils, and not shown in this pic- late below, with the
ture, winged ovary at B.
138
BEGINNERS’ BOTANY
gourd, pumpkin, the plant is monecious (‘in one house’’).
When they are on different plants, e.g. poplar, cottonwood,
we 57S ay
PEE SII My
FIG. 182. CATKINS OF A WILLOW.
A staminate flower is shown at s, and a
pistillate flower at #. The staminate
and pistillate are on different plants.
are irregular.
bois d’arc, willow (Fig. 182),
the plant is dicecious (“in two
houses”). Some varieties of
strawberry, grape, and mul-
berry are partly dicecious. Is
the rose either monoecious
or dicecious ?
Flowers in which the parts
of each series are alike are
said to be regular (as in Figs.
1735. )174,. 175). paehose san
which some parts are unlike
other parts of the same series
Their regularity may be in calyx, as in
nasturtium (Fig. 183); in corolla (Figs. 184, 185); in the
stamens (compare nasturtium, catnip,
Fig. 185, sage); in the pistils. Irregu-
larity is most frequent in the corolla.
Fic. 183. — FLOWER OF
GARDEN NASTURTIUM.
The
calyx is produced into a
spur.
Separate petal at a.
FLOWER OF
CATNIP.
FIG. 184.— THE FIVE PETALS
OF THE PANSY, detached to
show the form.
THE FLOWER—I1ITS PARTS AND FORMS 139
Various Forms of Corolla.— The corolla often assumes
very definite or distinct forms, especially when gamopet-
alous. It may have a long tube with a wide-flaring limb,
when it is said to be funnelform, as in morning-glory
and pumpkin. If the tube is very narrow and the limb
stands at right angles to it, the corolla is salverform, as
in phlox. If the tube is very short and the limb wide-
spreading and nearly circular in outline, the corolla is
rotate or wheel-shaped, as in potato.
A gamopetalous corolla or gamosepalous calyx is often
cleft in such way as to make two prominent parts. Such
parts are said to be lipped or labiate. Each of the lips or
lobes may be notched or toothed. In 5-membered flowers,
the lower lip is usually 3-lobed and the upper one 2-lobed.
Labiate flowers are characteristic of the mint family (Fig.
185), and the family therefore is called the Labiate. (Lit
erally, labiate means merely “lipped,” without specifying the
number of lips or lobes; but it is commonly used to desig-
nate 2-lipped flowers.) Strongly 2-parted polypetalous
flowers may be said to be labiate; but the term is often-
est used for gamopetalous co-
rollas.
Labiate gamopetalous flowers
that are closed in the throat (or
entrance to the tube) are said to
be grinning or personate (per-
g0mate means washed)« Snap: 21S 185---PERSoNATE FLOWER
5 , OF TOADFLAX.
dragon is a typical example;
also toadflax or butter-and-eggs (Fig. 186), and many
related plants. Personate flowers usually have defin-
ite relations to insect pollination. Observe how an
insect forces his head into the closed throat of the toad-
ai
168X.
I40 BEGINNERS’ BOTANY
The peculiar flowers of the pea tribes are explained in
Figs. 187, 188.
Spathe Flowers.—In many plants, very simple (often
naked) flowers are borne in dense, more or less fleshy
spikes, and the spike is inclosed in or attended. by a leaf,
sometimes corolla-like, known as a spathe. The spike of
flowers is technically known as a spadix. This type of
flower is characteristic of the great arum family, which is
Fic. 188. — DIAGRAM OF ALFALFA FLOWER
IN SECTION:
C, calyx, D, standard; W, wing; K, keel; 7, sta-
men-tube; /, filament of tenth stamen; X,
stigma; Y,style; O, ovary; the dotted lines at
FIG. 187. FLOWERS OF THE
COMMON BEAN, with one
flower opened (2) to show E show position of stamen-tube, when pushed
the structure, upward by insects. Enlarged.
chiefly tropical. _ The commonest wild representatives are
Jack-in-the-pulpit, or Indian turnip, and skunk cabbage. In
the former the flowers are all diclinous and naked. In the
skunk cabbage all the flowers are perfect and have four se-
pals. The common calla is a good example of this type of
inflorescence.
Composite Flowers.—The head (anthodium) or _ so-
called “flower” of sunflower (Fig. 189), thistle, aster,
dandelion, daisy, chrysanthemum, goldenrod, zs com-
posed of several or many little flowers, or florets. These
THE FLOWER—ITS PARTS AND’ FORMS I4I
florets are inclosed in a more or less dense and usually
green zxvolucre. In the thistle (Fig. 190) this involucre is
prickly. A longitudinal
section discloses the flo-
rets, all attached at bot-
tom to a common torus,
and densely packed in
the involucre. The pink
tips of these florets con-
stitute the showy part of
the head.
Each floret of the this-
tle (Fig. 190) is a com-
plete flower. Ata is the ovary. At 6 is a much-divided
plumy calyx, known as the pappus. The corolla is long-
tubed, rising above the pappus, and is enlarged and 5-lobed
FIG. 189. — HEAD OF SUNFLOWER.
at the top, c. The style pro-
jects:at.z. “The five anthers
are united about the style in
a ring at @. Such anthers
are said to be syngenesious.
These are the various parts
of the florets of the Com-
positz. In some cases the
pappus is in the form of
barbs, bristles, or scales, and
sometimes it is wanting.
The pappus, as we shall see
FIG. 190. — LONGITUDINAL SECTION later, assists in distributing
OF THISTLE HEAD; alsoa FLorer the seed. Often the florets
F THISTLE. :
OR ere are notallalike. Thecorolla
of those in the outer circles may be developed into a /ong,
straplike, or tubular part, and the head then has the ap-
142 BEGINNERS’? BOTANY
pearance of being one flower with a border of petals. Of
such is the sunflower (Fig. 189), aster, bachelor’s button or
cornflower, and field daisy (Fig. 211). These long corolla-
limbs are called rays. In some cultivated composites, all
the florets may develop rays, as in the dahlia and the chry-
santhemum. In some species, as dandelion, all the florets
naturally have rays. Syngenesious arrangement of an-
thers is the most characteristic single feature of the
composites.
Double Flowers. — Under the stimulus of cultivation and
increased food supply, flowers tend to become double.
True doubling arises
in two ways, mor-
phologically : (1)s¢a-
mens or pistils may
produce petals (Fig.
191); (2) adventt-
tious Or accessory
petals may arise in
the circle of petals.
Both these cate-
gories may be pres-
FIG. 191. — PETALS ARISING FROM THE STAMI-
NAL COLUMN OF HOLLYHOCK, and accessory ent in the same
petals in the corolla-whorl.
flower. In the full
double hollyhock the petals derived from the staminal col-
umn are shorter and make a rosette in the centre of. the
flower. In Fig. 192 is shown the doubling of a daffodil
by the modification of stamens. Other modifications of
flowers are sometimes known as doubling. For example,
double dahlias, chrysanthemums, and sunflowers are forms
in which the disk flowers have developed rays. The snow-
ball is another case. In the wild snowball the external
flowers of the cluster are large and sterile. In the culti-
THE FLOWER—ITS PARTS AND FORMS 143
vated plant all the flowers have become large and sterile.
Hydrangea is a similar case.
FIG. 192. — NARCISSUS OR DAFFODIL. Single flower at the right.
SuGGcEsTIONS.—145. If the pupil has been skilfully conducted
through this chapter 4y means of careful study of specimens rather
than as a mere memorizing process, he will be in mood to chal-
lenge any flower that he sees and to make an effort to understand
it. Flowers aré endlessly modified in form; but they can be
understood if the pupil looks first for the anthers and ovaries.
How may anthers and ovaries always be distinguished? 146. It is
excellent practice to find the flowers in plants that are commonly
known by name, and to determine the main points in their struc-
ture. What are the flowers in Indian corn? pumpkin or squashP
celery? cabbage? potato? pea? tomato? okra? cotton? rhubarb?
chestnut? wheat? oats? 147. Do all forest trees have flowers?
Explain. 148. Name all the moncecious plants you know.
Dicecious. 149, What plants do you know that bloom before
the leaves appear? Do any bloom after the leaves fall? 150. Ex-
plain the flowers of marigold, hyacinth, lettuce, clover, asparagus,
garden calla, aster, locust, onion, burdock, lily-of-the-valley, crocus,
Golden Glow, rudbeckia, cowpea. 151. Define a lower.
Notre TO THE TEACHER.—It cannot be urged too often that
the specimens themselves be studied. If this chapter becomes a
mere recitation on names and definitions, the exercise will be
worse than useless. Properly taught by means of the flowers
themselves, the names become merely incidental and: a part of
the pupil’s language, and the subject has living interest.
GHAPTER? XTX
THE FLOWER—FERTILIZATION AND POLLINATION
Fertilization. — Seeds result from the union of two ele-
ments or parts. One of these elements is a cell-nucleus
eee A °
o
FIG. 193. — B, POLLEN escap-
ing from anther; J, pollen
germinating on a stigma.
Enlarged.
or union of a nucleus of the pollen and the
nucleus of the egg-cell in the ovule, takes place.
The ovule and embryo within then develops
into a seed. The growth of the pollen-tube is
often spoken of as germination of the pollen,
but it is not germination in the sense in which
the word is used when speaking of seeds.
Better seeds — that is, those that produce
stronger and more fruitful plants — often re-
Fertilization effected between different flowers
of the pollen-grain. The other ele-
ment is the cell-nucleus of an egg-
Cell, sborne sine the jovanyer uae
pollen-grain falls on the stigma
(Fig. 193). It absorbs the juices
exuded by the stigma, and grows
by sending out a tube (Fig. 194).
This tube grows downward through
the style, absorbing food as it goes,
and finally reaches the egg-cell in
the interior of an ovule in the
ovary (Fig. 195), and fertilization,
FIG. 194. —
sult when the pollen comes from another flower. —& PoLiEN-
GRAIN AND
THE GROW:
is cross-fertilization; that resulting from the ine Tusr,
144
THE FLOWER— FERTILIZATION AND POLLINATION 145
application of pollen to pistils in the same flower is close-
fertilization or self-fertilization. It will be seen that the
cross-fertilization relationship may be of many degrees—
between two flowers in the same cluster, between those
in different clusters on the same
branch, between those on different
plants. Usually fertilization takes
place only between plants of the
same species or kind.
In many cases there is, in effect,
an apparent selection of pollen when
pollen from two or more sources is
applied to the stigma. Sometimes
the foreign pollen, if from the same
kind of plant, grows, and fertiliza-
tion results, while pollen from the
FIG. 195.— DIAGRAM TO
. : REPRESENT FERTILIZA-
tive. If, however, no foreign pol- TION.
same flower is less promptly effec-
len is present, the pollen from the © s,stigma; s¢,style; ov, ovary; 0,
ovule; %, pollen-grain; Z2,
same flower may finally serve the pollen tubes ves eee cellot aa
same purpose. miccopyle.
In order that the pollen may grow, ¢he stigma must be
ripe. At this stage the stigma is usually moist and some-
times sticky. A ripe stigma is said to be receptive. The
stigma may remain receptive for several hours or even
days, depending on the kind of plant, the weather, and how
soon pollen is received. Watch a certain flower every day
to see the anther locules open and the stigma ripen. When
fertilization takes place, the stigma dies. Observe, also,
how soon the petals wither after the stigma has received
pollen. .
Pollination.—The transfer of the pollen from anther
to stigma is known as pollination. The pollen may
L
146 BEGINNERS’ BOTANY
fall of its own weight on the adjacent stigma, or it
may be carried from flower to flower by wind, insects, or
other agents. There may be self-pollination or cross-pol-
lination, and of course it must always precede fertilization.
Usually the pollen is discharged by the burst-
é ing of the anthers. The commonest method of
discharge is through a s/¢¢ on either side of the
anther (Fig. 193). Sometimes it discharges
Pra Ue through a fore at the apex, as in azalea (Fig.
Antuer or 196), rhododendron, huckleberry, wintergreen.
gee In some plants a part of the anther wall raises
terminal OF falls asa Zd, as in barberry (Fig. 197), blue
pores. -cohosh, May apple. The opening of an anther
(as also of a seed-pod) is known as dehiscence (de, from ;
hisco, to gape). When an anther or seed pod opens, it is
said to dehisce.
Most flowers are so constructed as to increase the chances
of cross-pollination. We have seen that the stigma may
have the power of choosing foreign pollen. The
commonest means of necessitating cross-pollina-
tion is the different times of maturing of stamens
and pistils in the same flower. In most cases
the stamens mature first: the flower is then
proterandrous. When the pistils mature first,
the flower is proterogynous. (Azer, andr, is a
3 ‘ FIG. 197.-—-
Greek root often used, in combinations, for sta- Barperry
men, and gyze for pistil.) The difference in STAMEN,
time of ripening may be an hour or two, or it Sagas
may be a day. The ripening of the stamens nde.
and the pistils at different times is known as dichogamy, and
flowers of such character are said to be dichogamous.
There is little chance for dichogamous flowers to pollinate
themselves. Many flowers are zmperfectly dichogamous —
THE FLOWER—FERTILIZATION AND POLLINATION 147
some of the anthers mature simultaneously with the pistils,
so that there is chance for self-pollination in case for-
eign pollen does
not arrive. Even
when the stigma
receives pollen
from its own
flower, cross-fer-
tilization may
result. The hol-
lyhock is proter-
androus. Big:
198 shows a
flower recently
expanded. The centre is occupied. by the column of sta-
mens. In Fig. 199, showing an older flower, the long
FIG. 198.— FLOWER OF HOLLYHOCK; proterandrous,
styles are conspicuous.
Some flowers are so constructed as to prohibit self-pollt-
nation. Nery irregular flowers are usually of this kind.
With some of them,
the petals form a
sac to inclose the
anthers and the pol-
len cannot be shed
on the stigma but is
retained until a bee
forces the sac open;
the pollen is rubbed
on the hairs of the
bee and transported.
FIG, 199. —OLDER FLOWER OF HOLLYHOCK,
Regular flowers usu-
ally depend mostly on dichogamy and the selective power
of the pistil to insure crossing /lowers that are very
148 BEGINNERS’ BOTANY
irregular and provided with nectar and strong perfume are
usually pollinated by insects. Gaudy colours probably at-
tract insects in many cases, but perfume appears to be a
creater attraction.
The insect vzszts the flower for the
nectar (for the making of honey) and
may unknowingly carry the pollen.
Spurs and sacs in the flower are necta-
ries (Fig. 200), but in spurless flowers
the nectar is usually secreted 7” the
bottom of the flower cup. This compels
the insect to pass by the anther and
Fic, 200.— FLower oF rub against the pollen before it reaches
Bee the nectar. Sometimes the anther is a
=
SB
‘
SA
sins
G \\\
Z ZAN\\\\
a
AY
ut
long lever poised on the middle point and the insect
bumps against one end and lifts
it, thus bringing the other end
of the lever with the pollen sacs
down on its back. Flowers that
are pollinated by insects are said
to be entomophilous (‘‘ insect lov-
ing’). Fig.200showsa larkspur.
The envelopes are separated in
Fig. 201. The long spur at once
suggests insect pollination. The
spur is a sepal. Two hollow
petals project into this spur, ap- FIG. 201. — ENVELOPES OF A
parently serving to guide the LARKSPUR. There are five
’ wide sepals, the upper one be-
bee’s tongue. The two smaller ing spurred. There are four
petals, in front, are peculiarly small petals.
coloured and perhaps serve the bee in locating the nectary.
The stamens ensheath the pistils (Fig. 202). As the insect
stands on the flower and thrusts its head into the centre,
THE FLOWER—FERTILIZATION AND POLLINATION 149
the envelopes are pushed downward and outward and
the pistil and stamens come in contact with its abdomen.
Since the flower is proterandrous, the
pollen that the pistils receive from the
bee’s abdomen must come from another
flower. Note a somewhat similar ar-
rangement in the toadflax or butter-and-
eggs.
In some cases (Fig. 203) the stamens
are longer than the pistil in one flower
and shorter in another. If the insect
visits such flowers, it gets pollen on its
head from the long-stamen flower, and
deposits this pollen on the stigma in the
long-pistil flower. Such flowers are di-
FIG. 202. — STAMENS
OF LARKSPUR, sur-
rounding the pistils.
morphous (of two forms). If pollen from its own flower
and from another flower both fall on the stigma, the proba-
bilities are that the stigma will choose the foreign pollen.
< N ui A
FIG. 203.— DIMORPHIC FLOWERS OF PRIMROSE.
Many flowers are pollinated by the wind. They are said
to be anemophilous (‘‘ wind loving”’),
Such flowers pro-
150 BEGINNERS’ BOTANY
duce great quantities of pollen, for much of it is wasted.
They usually have broad stigmas, which expose large
surfaces to the wind. They are usually lacking in gaudy
colours and in perfume. Grasses and pine trees are typical
examples of anemophilous plants.
In many cases cross-pollination is assured because the
stamens and the pistils are in different flowers (diclinous).
Monececious and
dicecious plants
may be ~ polli-
ify nated by wind or
. Age insects, or other
< _ agents (Fig. 204).
They are usually
wind - pollinated,
REX
PD
wens
pa
us TaN
ut:
LP >.
although willows
are often, if not
mostly, _insect-
pollinated. The
Indian corn is a
monececious plant.
The staminate
FIG. 204.— FLOWERS OF BLACK WALNUT: two pis- flowers are in a
tillate flowers at 4, and staminate catkins at 5. f ,
terminal panicle
(tassel). The pistillate flowers are in a dense spike (ear),
inclosed in a sheath or%husk. Each “silk” is a style:
Each pistillate flower produces a kernel of corn. Some-
times a few pistillate flowers are borne in the tassel and a
few staminate flowers on the tip of the ear. Is self-fertili-
zation possible with the corn? Why does a “volunteer”
stalk standing alone in a garden have only a few grains
on the ear? What is the direction of the prevailing wind
in summer? If only two or three rows of corn are
THE FLOWER— FERTILIZATION AND POLLINATION 151
planted in a garden where prevailing winds occur, in which
direction had they better run?
Although most flowers are of such character as to insure
or increase the chances of cross-pollination, there are some
that absolutely forbid crossing. These flowers are usually
borne beneath or on the
ee
ground, and they lack feo
ee Ses
showy colours and _ per- i
\
fumes. They are known
as cleistogamous flowers
(meaning self-fertilizing
flowers). The plant has
normal showy flowers
that may be insect-pol-
linated, and in addition
is provided with these
simplified flowers. Only
a few plants bear cleis-
togamous flowers. Hog-
peanut, common _ blue
violet, fringed winter-
green, and dalibarda are FIG. 205.—CoMMON BLUE VIOLET. The
familiar flowers are shown, natural size.
The corolla is spurred. Late in the season,
this country. Fig. cleistogamous flowers are often borne on
4 the surface of the ground. A small one is
205 shows a cleistoga- shown at a. A nearly mature pod is shown
mous flower of the blue at 6. Both a and @ are one third natural
: size.
violet at a. Above the
true roots, slender stems bear these flowers, that are
the best subjects in
provided with a calyx, and a curving corolla which does
not open. Inside are the stamens and the pistils. Late in
the season the cleistogamous flowers may be found just
underneath the. mould. ‘They mever vice above ground.
m ne a3 en lls : ‘
The following summer one may find a seedling plant, in
152 BEGINNERS’? BOTANY
some kinds of plants, with the remains of the old cleistog-
amous flower still adhering to the root.
Cleistogamous
flowers usually appear after the showy flowers have
Fic. 206.— PODS OF PEANUTS RIPENING UNDERGROUND,
passed. They seem to insure a crop
of seed by a
method that expends little of the plant’s energy. The
pupil will be interested to work out the fruiting of the pea-
FIG. 207. —STRUGGLE FOR EXISTENCE AMONG THE
APPLE FLOWERS.
nut (Fig. 206).
Unbaked fresh
peanuts grow
readily and can
easily be raised
in Canada. in
a warm sandy
garden.
SUGGESTIONS. —
152. Wot all the
flowers produce
seeds. Note that
an apple tree may
bloom very full,
but that only rela-
tively few apples
may result (Fig. 207). ore poilen is produced than ts needed to
Jertilize the flowers; this increases the chances that sufficient
THE FLOWER—FERTILIZATION AND POLLINA7/0N_ 153
stigmas will receive acceptable pollen to enable the plant to
perpetuate its kind. At any time in summer, or even in fall,
examine the apple trees carefully to determine whether any dead
flowers or flower stalks still remain about the apple ; or, examine
any full-blooming plant to see whether any of the flowers fail.
153. Keep watch on any plant to see whether insects visit it.
What kind? When? What for? 154. Determine whether the
calyx serves any purpose in protecting the flower. Very carefully
remove the calyx from a bud that is normally exposed to heat
and sun and rain, and see whether the flower then fares as well as
others. 155. Cover a single flower on its plant with a tiny paper
or muslin bag so tightly that no insect can get in. If the flower
sets fruit, what do you conclude? 156, Remove carefully the
corolla from a flower nearly ready to open, preferably one that has
no other flowers very close to it. Watch for insects. 157. Find
the nectar in any flower that youstudy. 158. Remove the stigma.
What happens? 159. Which of the following plants have perfect
flowers: pea, bean, pumpkin, cotton, clover, buckwheat, potato,
Indian corn, peach, chestnut, hickory, watermelon, sunflower, cab-
bage, rose, begonia, geranium, cucumber, calla, willow, cotton-
wood, cantaloupe? What have the others? 160. On wind-
pollinated plants, are either anthers or stigmas more numerous ?
161. Are very small coloured flowers usually borne singly or in
clusters? 162. Why do rains at blooming time often lessen
the fruit crop? 163. Of what value are bees in orchards ?
164. Zhe crossing of plants to improve varieties or to obtain new
varieties. —It may be desired to perform the operation of polli-
nation by hand. In order to insure the most definite results,
every effort should be made rightly to apply the pollen which it
is desired shall be used, and rigidly to exclude all other pollen.
(a) The first requisite is to remove the anthers from the flower
which it is proposed to cross, and they must be removed before the
pollen has been shed. The flower-bud is therefore opened and the
anthers taken out. Cut off the floral envelopes with small, sharp-
pointed scissors, then cut out or pull out the anthers, leaving only
the pistil untouched ; or merely open the corolla at the end and
pull out the anthers with a hook or tweezers ; and this method is
often the best one. It is best to delay the operation as long as
possible and yet not allow the bud to open (and thereby expose
the flower to foreign pollen) nor the anthers to discharge the
pollen. (4) The flower must next be covered with a paper bag to
prevent the access of pollen (Figs. 208, 209). If the stigma is not
receptive at the time (as it usually is not), the desired pollen is
not applied at once. The bag may be removed from time to time
to allow of examination of the pistil, and when the stigma is
mature, which is told by its glutinous or roughened appearance,
154 BEGINNERS’ BOTANY
the time for pollination has come. If the bag is slightly moist-
ened, it can be puckered more tightly about the stem of the plant.
The time required for the stigma to mature varies from several
hours to a few days. (c) When the stigma is ready, an unopened
anther from the desired flower is crushed on the finger nail or a
knife blade, and the pollen is rubbed on the stigma by means of a
tiny brush, the point of a knife blade, or a sliver of wood. The
FIG. 208.— A PAPER BAG, FIG. 209.— THE BAG TIED
with string inserted. OVER A FLOWER.
flower is again covered with the bag, which is allowed to remain
for several days until all danger of other pollination is past. Care
must be taken completely to cover the stigmatic surface with
pollen, if possible. ‘The seeds produced by a crossed flower pro-
duce hybrids, or plants having parents belonging to different
varieties or species. 165. One of the means of securing new
forms of plants is by making hybrids. Why Pe
Fic. 210. — The fig is a hol'!ow torus with flowers borne on the inside,
and pollinated by insects that en er at the apex.
CHAPTER. 2x
FLOWER-CLUSTERS
Origin of the Flower-cluster.— We have seen that
branches arise from the axils of leaves. Sometimes the
leaves may be reduced to bracts
and yet branches are borne in
their axils. Some of the branches
grow into long limbs; others be-
come short spurs; others bear
flowers. In fact, a flower is it-
self a specialized branch.
Flowers are usually borne
near the top of the plant. Often
they are produced in great num-
bers. It results, therefore, that
flower branches usually stand
close together, forming a clus-
ter. The shape and the arrange-
ment of the flower-cluster affer
with the kind of plant, since
each plant has its own mode of
branching.
Certain definite or well-marked
types of flower-clusters have re-
ceived names. Some of these
names we shall discuss, but the
FIG, 211. — TERMINAL FLOWERS
OF THE WHITEWEED (in some
places called ox-eye daisy).
flower-clusters that perfectly match the definitions are the
exception rather than the rule.
155
The determining of the
156 BEGINNERS’ BOTANY
kir 4s of flower-clusters is one of the most perplexing stb-
jects in descriptive botany. We may classify the subject
aronnd three ideas: solitary flowers, centrifugal or deter-
minate clusters, centripetal or indeterminate clusters.
Solitary Flowers.—In many cases flowers are borne
singly; they are separated from other flowers by leaves.
They are then said to be solitary. The solitary flower may
be either at the end of the
main shoot or axis (Fig. 211),
when it is said to be terminal ;
or from the side of the shoot
(Fig. 212), when it is said to
be lateral or axillary.
Centripetal Clusters. — If
the flower-bearing axils were
rather close together, an open
or leafy flower-cluster might
result. If the plant continues
to grow from the tip, the
older flowers are left farther
and farther behind. If the
cluster were so short as to be
FIG. 212.— LATERAL FLOWER OF
AN ABUTILON. A greenhouse flat or convex on top, the out-
plant.
ermost flowers would be the
older. A flower-cluster in which the lower or outer flowers
open first is said to be a centripetal cluster. It is some-
times said to be an indeterminate cluster, since it is the
result of a type of growth which may go on more or less
continuously from the apex.
The simplest form of a definite centripetal cluster is a
raceme, which is an open elongated cluster in which the
flowers are borne singly on very short branches and open
from below (that is, from the older part of the shoot)
FLOWER-CLUSTERS 157
upwards (Fig. 213). The raceme may be zermznaé to the
main branch; or it may be /azera/ to it, as in Fig. 214
Racemes often bear the
flowers on one side of
NG
NANNY AXP 7
~ AW Wie),s ‘ is
EAN wW HD the stem, thus form
XM ing a single row.
When a cen-
tripetal flower-
yn cluster is long
Ay" and dense and
the flowers are
sessile or nearly so,
it is called a spike
(Fig. 215). Common
examples of spikes
are plantain, migno-
“| | SA
Cd PASS QQ . ANN
\\\ Sy)
SSA)
<\
I OSs
nette, mullein.
A very short and
dense spike is a head.
Clover. (Fig? '216)°1s
a goodexample. The
sunflower: and related
FIG, 213.— RACEME OF CURRANT. plants bear many
Terminal or lateral ? small flowers in a
very dense and often flat head. Note that in the
sunflower (Fig. 189) the outside or exterior flowers
FIG, 215.—
SPIKE OF
Fic. 214. — LATERAL RACEMES (in fruit) OF BARBERRY. PLANTAIN,
158 BEGINNERS’ BOTANY
open first. Another special form of spike is the catkin,
which usually has scaly bracts, the whole cluster being
deciduous after flowering or fruiting, and the flowers (in
typical cases) having only stamens or pistils. Examples
are the “pussies” of willows (Fig.
182) and flower-clusters of oak (Fig.
180), walnuts (Fig. 204), poplars.
FIG. 216.— HEAD OF CLO- FIG. 217.—-CORYMB OF CANDY-
VER BLOSSOMS. TUFT.
When a loose, elongated centripetal flower-cluster has
some primary branches simple, and others irregularly
branched, it is called a panicle. It is a branching raceme.
Because of the earlier growth of the lower branches, the
panicle is usually broadest at the base or conical in outline.
True panicles are not very common.
When an indeterminate flower-cluster is short, so that
FLOWER-CLUSTERS [59
the top ts convex or flat, it is a corymb (Fig. 217). The
outermost flowers open first. Centripetal flower-clusters
are sometimes said to be corymbose in mode.
When the branches of an indeterminate cluster arzse from
a common point, like the frame of an umbrella, the cluster
is an umbel (Fig. 218). Typical umbels occur in carrot,
parsnip, caraway, and other plants of the parsley family:
the family is known as the Umbelliferae, or umbel-bearing
FIG. 218. — REMAINS OF A LAST YEAR’S UMBEL OF WILD CARROT.
family. In the carrot and many other Umbelliferz, there
are small or secondary umbels, called umbellets, at the end
of each of the main branches. (In the centre of the wild
carrot umbel one often finds a single, blackish, often
aborted flower, comprising a 1I-flowered umbellet.)
Centrifugal or Determinate Clusters. — When the ter-
minal or central flower opens first, the cluster is said to be
centrifugal. The growth of the shoot or cluster is deter-
minate, since the length is definitely determined or stopped
by the terminal flower. Fig. 219 shows a determinate or
centrifugal mode of flower bearing.
160 BEGINNERS’ BOTANY
Dense centrifugal clusters are
usually flattish on top because of
the cessation of growth in the
main or central axis. These com-
pact flower-clusters are known
as cymes. Centrifugal clusters
are sometimes said to be cymose
in mode. Apples, pears (Fig.
220), and elders bear flowers in
cymes. Some cyme-forms are
like umbels in general appear-
ance. A head-like cymose clus-
ter is a glomerule; it blooms from
the top downwards rather than
from the base upwards.
Mixed Clusters. — Often the
cluster is mixed, being determi-
FIG. 219.— DETERMINATE OR ; : ;
CYMOsE ARRANGEMENT.— Nate in one part and indeterminate
eae in another part of the same clus-
ter. The main cluster may be indeterminate, but the
branches determinate. The cluster has the appearance of
a panicle, and is usually so called, but it is really a thyrse.
Lilac is a familiar example of a
thyrse. In some cases the main
cluster is determinate and the
branches are indeterminate, as in
hydrangea and elder.
Inflorescence. — The mode or
method of flower arrangement is
known as the inflorescence. That ie. oo0.—CymeE or PEAR.
is, the inflorescence is cymose, co- Often imperfect.
rymbose, paniculate, spicate, solitary, determinate, inde-
terminate. By custom, however, the word “inflorescence ”
FLOWER-CLUSTERS 161
ms eran har 2 oA
FiG. 221.— FORMS OF CENTRIPETAL FLOWER-CLUSTERS,
I, raceme; 2, spike; 3, umbel; 4, head or anthodium; 5, corymb.
FIG, 222, — CENTRIPETAL INFLORESCENCE, continued.
6, spadix; 7, compound umbel; 8, catkin.
9
>
FIG, 223. — CENTRIFUGAL INFLORESCENCE.
1,cyme; 2, scirpioid raceme (or half cyme),
t62 BEGINNERS’ BUTANY
has come to be used in works on descriptive botany for
the flower-cluster itself. Thus a cyme or a panicle may be
called an inflorescence. It will be seen that even solitary
flowers follow either indeterminate or determinate methods
of branching.
The flower-stem.— The stem of a solitary flower is
known as a peduncle; also the general stem of a flower-
cluster. The stem of the individual flower in a cluster is
a pedicel. In the so-called stemless: plants the peduncle
may arise directly from the ground, or crown of the plant,
as in dandelion, hyacinth, garden daisy; this kind of
peduncle is called a scape. A scape may bear one or
many flowers. It has no foliage leaves, but it may have
bracts.
SUGGESTIONS. —166. Name six columns in your notebook as
follows: spike, raceme, corymb, umbel, cyme, solitary. Write
each of the following in its appropriate column: larkspur, grape,
rose, wistaria, onion, bridal wreath, banana, hydrangea, phlox,
China berry, lily-of-the-valley, Spanish dagger (or yucca), sorghum,
tuberose, hyacinth, mustard, goldenrod, peach, hollyhock, mul-
lein, crépe myrtle, locust, narcissus, snapdragon, peppergrass,
shepherd’s purse, coxcomb, wheat, hawthorn, geranium, carrot,
elder, millet, dogwood, castor bean ; substitute others for plants
that do not grow in your region. 167. In the study of flower-
clusters, it is well to choose first those that are fairly typical of the
various classes discussed in the preceding paragraphs. As soon
as the main types are well fixed in the mind, random clusters
should be examined, for the pupil must never receive the impres-
sion that all flower-clusters follow the definitions in books. Clus-
ters of some of the commonest plants are very puzzling, but the
pupil should at least be able to discover whether the inflorescence
is determinate or indeterminate. Figures 221 to 223 illustrate the
theoretical modes of inflorescence. The numerals indicate the order
of opening.
CHAPTER (XX!
FRUITS
THE ripened ovary, with its attachments, is known as the
fruit. /¢ contains the seeds. If the pistil is simple, or of
one carpel, the fruit
also will have one com-
partment. If the pistil
is compound, or of
more than one carpel,
the fruit usually has an
equal number of com-
partments. The com-
partments in pistil and
fruit are known as lo-
cules (from Latin /ocus,
meaning “a place’’).
The simplest kind
of fruit is a rzpened
1-loculed ovary. “The
first stage in complex-
ity is a ripened 2- or
FIG. 224.— DENTARIA, OR TOOTH-WORT, in
fruit.
many-loculed ovary. Nery complex forms may arise by the
attachment of other parts to the ovary. Sometimes the style
persists and becomes a beak (mustard pods, dentaria,
Fig. 224), or a tail as in clematis; or the calyx may be
attached to the ovary; or the ovary may be embedded in
the receptacle, and ovary and receptacle together consti-
tute the fruit: or an involucre may become a part of the
163
I 64 BEGINNERS’ BOTANY
fruit, as possibly in the walnut and the hickory (Fig. 225),
and the cup of the acorn (Fig. 226). The chestnut and the
beech bear a prickly involucre, but the nuts,
: a, y
FIG, 225. — HICKORY-NUT. FIG, 226.— LIVE-OAK ACORN.
The nut is the fruit, con- The fruit is the “seed” part;
tained in a husk. the involucre is the ‘‘ cup.”
or true fruits, are not grown fast to it, and the involucre
can scarcely be called a part of the fruit. A ripened ovary
is a pericarp. A pericarp to which other parts adhere has
been called an accessory or reénforced fruit. (Page 169.)
Some fruits are dehiscent, or split open at maturity and
liberate the seeds; others are indehiscent, or do not open.
A dehiscent pericarp is called a / pod.
The parts into which such
a pod breaks or splits are
known as valves. In inde-
hiscent fruits the seed is
liberated by the decay of
the envelope, or by the
rupturing of the envelope
i - FIG, 228. — KEY
FIG. 227. KEY OF by the germinating seed. oF COMMON
SUGAR MAPLE, Indehiscent winged peri- AMERICAN ELM,
carps are known as samaras or key fruits. Maple (Fig.
227), elm (Fig. 228), and ash (Fig. 93) are examples.
FRUITS © 165
Pericarps.— The simplest pericarp is a dry, one-
seeded, indehiscent body. It is known as an akene. A
head of akenes is shown in Fig. 229, and the
structure is explained in Fig.
230. Akenes may be seen in
buttercup, hepatica, anemone,
smartweed, buckwheat.
Ree A t-loculed pericarp which eee
Axenrsor dehisces along the front edge one in longitudi-
BO TER CUES (that is, the inner edge, next nal section.
the centre of the flower is a follicle. The fruit of the
larkspur (Fig. 231) is a follicle. There are usually five of
these fruits (sometimes three or
four) in each larkspur flower, each
pistil ripening into a follicle. If
these pistils were united, a single
compound pistil would be formed.
Columbine, peony, ninebark, milk-
weed, also have follicles.
FIG. 231.— A t-loculed pericarp that de-
FOLLICLE : :
or Lark- hisces on both edges is a legume.
SPUR. Peas and beans are typical exam-
ples (Fig. 232); in fact, this character gives
name to the pea family, — Leguminose.
Often the valves of the
legume twist forcibly and
expel the seeds, throwing Fic. 232.—A
them some distance. The BEAN PoP:
word “pod” is sometimes restricted to
legumes, but it is better to use it generi-
FIG. 233. — CAPSULE OF : :
Gicionomli@ean cally forall dehiscent pericarps.
AFTER DEHISCENCE. = A compound pod —dehiscing peri-
carp of two or more carpels — is a capsule (Figs. 233, 234,
166 BEGINNERS’ BOTANY
236, 237). Some capsules are of one
locule, but they may have been compound
when young (in the ovary stage) and the
partitions may have vanished. Sometimes
one or more of the carpels are uniformly
crowded out by the exclusive growth of
other carpels (Fig. 235). The seeds or
parts which are crowded out are said to
FIG. 234.— Cap- be aborted.
SULE OF MORN- There are several ways in which cap-
ING GLORY,
sules dehisce or open. When they break
along the partitions (or septa), the mode is known as septi-
cidal dehiscence (Fig. 236);
In septicidal dehiscence the
fruit separates into parts
representing the original
carpels. These carpels
may still be entire, and FIG. 235. — THREE-CARPELED FRUIT
they then dehisce individu- OF HORSE-CHESTNUT. Two locules
are closing by abortion of the ovuies,
ally, usually along the inner
edge as if they were follicles. When the compartments
split in the middle, between the
partitions, the mode is loculicidal
dehiscence (Fig. 237). In some
cases the dehiscence is at the top,
. when it is said to be apical (al-
though several modes of dehis-
FIG, 236. — FIG, 237.— i 5
Shc récunion ~ cence: are hereuncluded) a Wien
Wort. Sep- DAL Popor the whole top comes off, as in purs-
ticidal. DAY-LILY.
lane and garden portulaca (Fig.
238), the pod is known as a pyxis. In some cases apical
dehiscence is by means of a hole or clefts.
The peculiar capsule of the mustard family, or Cruci
FRUITS 167
ferze, is known as a silique when it is distinctly longer than
broad (Fig. 224), and a silicle when its breadth nearly
FIG. 238. — PYXIS OF PORTU- FIG. Ee eomrRnG OF GOOSE-
LACA OR ROSE-MOSS. BERRY. Remains of calyx atc.
equals or exceeds its length. A cruciferous capsule is
2-carpeled, with a thin partition, each locule containing
seeds in two rows. The two valves detach from below
upwards. Cabbage, turnip, mustard, water-cress, radish, .
rape, shepherd’s purse,
sweet alyssum, wall-
flower, honesty, are
examples.
FIG. 240.— BERRY OF THE GROUND CHERRY
OR HUSK TOMATO, contained in the inflated
calyx.
The pericarp may be fleshy and
indehiscent. A pulpy pericarp
with several or many seeds is a
berry (Figs. 239, 240, 241). To
the horticulturist a berry is a
; ‘ : Fic, 241.— ORANGE; example
small, soft, edible fruit, without of a Lerry.
168 BEGINNERS’ BOTANY
particular reference to its structure. The botanical and
horticultural conceptions of a berry are, therefore, unlike.
In the botanical sense, gooseberries, currants, grapes, to-
matoes, potato-balls, and even eggplant fruits and oranges
(Fig. 241) are berries; strawberries, raspberries, black-
berries are not.
A fleshy pericarp containing one relatively large seed
or stone is a drupe. Examples are plum (Fig. 242), peach,
cherry, apricot, olive. The walls of
the pit in the plum, peach, and cherry
are formed from the inner coats of
the ovary, and the flesh from the
outer coats. Drupes are also known
as stonefrutts.
Fruits that are formed by the sub-
FIG. 242.— PLUM; exam- sequent union of separate pistils are
Bicone erie. aggregate fruits. The carpels in
aggregate fruits are usually more or less fleshy. In the rasp-
berry and the blackberry flower, the pistils are essentially
distinct, but as the
pistils ripen they co-
here and form one
body (Figs. 243, 244).
FIG, 243. — FRUIT OF RASP-
BERRY.
Each of the carpels or pistils in the
raspberry and the blackberry is a
little drupe or drupelet. In the
raspberry the entire fruit separates
FIG, 244. — AGGREGATE from the torus, leaving the torus on
FRUIT OF MULBERRY;
and a separate fruit.
the plant. In the blackberry and
FRUITS 169
the dewberry the fruit adheres to the torus, and the two are
removed together when the fruit is picked.
Accessory Fruits.— When the pericarp and some other
part grow together, the fruit is said to be accessory or
reenforced. An example is the straw-
berry (Fig. 245). The edible part is a
greatly exlarged torus, and the pericarps
are akenes embedded in it. These akenes
are commonly called seeds.
Various kinds of reénforced fruits have
received special names. One of these is
the hip, characteristic of roses. In this
eke meg case, the torus is deep and hollow, like an
torus inwhich akenes urn, and the separate akenes are borne
are embedded.
inside it. The mouth of the receptacle
may close, and the walls sometimes become fleshy; the
fruit may then be mistaken for a-berry. The fruit of the
pear, apple, and quince is known as a
FIG. 246.— SECTION OF FIG. 247. -— CROSS-SECTION
AN APPLE. OF AN /.PPLE,
pome. In this case the five united carpel; are completely
buried in the hollow torus, and the torus makes most of
the edible part of the ripe fruit, while the pistils are repre-
sented by the core (Fig. 246). Observe the sepals on the
top of the torus (apex of the fruit) in Fig. 246. Note
the outlines of the embedded pericarp in Fig. 247.
170 BEGINNERS’ BOTANY
Gymnospermous Fruits. —In pine, spruces, and their kin,
there is no fruit in the sense in which the word is used
in the preceding pages, because ¢here zs no ovary. The
ovules are naked or uncovered, in the axils of the scales of
the young cone, and they have neither style nor stigma.
The pollen falls directly on the mouth of the ovule. The
ovule ripens into a seed, which is usually winged. Because
the ovule is not borne in a sac or ovary, these plants are
called gymnosperms (Greek for ‘“‘naked seeds’’). All the
true cone-bearing plants are of this class; also certain
other plants, as red cedar, juniper, yew. The plants are
moncecious or sometimes dicecious. The staminate flowers
are mere naked stamens borne beneath scales, in small
yellow catkins which soon fall. The pistillate flowers are
naked ovules beneath scales on cones that persist (Fig.
29). Gymnospermous seeds may have several cotyledons.
SUGGESTIONS.—168. Study the following fruits, or any five fruits
chosen by the teacher, and answer the questions for each: Apple,
peach, bean, tomato, pumpkin. What is its form? Locate the
scar left by the stem. Bv what kind of stem was it attached?
Are there any remains of the blossom at the blossom end? De-
scribe texture and colour of surface. Divide the fruit into the seed
vessel and the surrounding part. Has the fruit any pulp or flesh?
Ts it within or without the sced vessel? Is the seed vessel simple
or sub-divided? What is the number of seeds? Are the seeds
free, attached to the wall of the vessel, or to a support in the
centre? Are they arranged in any order? What kind of wall has
the seed vessel? What is the difference between a peach stone
and a peach seed? 169. The nut fruits are always available for
study. Note the points suggested above. Determine what the
meat or edible part represents, whether cotyledons or not. Figure
248 is suggestive. 170- Mention all the fleshy fruits you know,
tell where they come from, and refer them to their proper groups.
171. What kinds of fruit can you buy in the market, and to what
groups or classes do they belong? Of which fruits are the seeds
only, and not the pericarps, eaten? 172. An ear of corn is always
available for study. What is it—a fruit or a collection of fruits?
How are the grains aranged on the cob? How many rows do
you count on each of several ears? Are all the rows on an ear
FRUITS 17
equally close together? Do you find an ear with an odd number
of rows? How do the parts of the husk overlap? Does the
husk serve as protection from rain? Can birds pick out the grains?
How do insect enemies enter the ear? How and when do weevils
lay eggs on corn? 173. Study a grain of corn. Is it a seed?
Describe the shape of a grain. Colour. Size. Does its surface
show any projections or depressions? Is the seed-coat thin or
thick? Transparent or opaque? Locate the hilum. Where is
the silk scar? What is the silk? Sketch the grain from the two
points of view that show it best. Where is the embryo? Does
the grain have endosperm ? What is dent corn? Flint corn?
How many kinds of corn do you know? For what are they used?
FIG. 248.— PECAN
FRUIT.
Note TO TEACHER.—There are few more interesting subjects
to beginning pupils than fruits,—the pods of many kinds, forms,
.and colours, the berries, and nuts. This interest may well be
utilized to make the teaching alive. All common edible fruits
of orchard and vegetable garden should be brought into this dis-
cussion. Of dry fruits, as pods, burs, nuts, collections may be
made for the school museum. Fully mature fruits are best for
study, particularly if it is desired to see dehiscence. For com-
parison, pistils and partially grown fruits should be had at the
same time. If the fruits are not ripe enough to dehisce, they
may be placed in the sun to dry. In the school it is well to have
a collection of fruits for study. The specimens may be kept in
glass jars. Always note exterior of fruit and its parts; interior
of fruit with arrangement and attachment of conients.
CHAPTER XXII
DISPERSAL OF SEEDS
It is to the plant’s advantage to have its seeds distributed
as widely as possible. Jt has a better chance of surviving
in the struggle for existence. It gets away from competi-
tion. Many seeds and fruits are of such character as to
increase their chances of wide dispersal. The commonest
means of dissemination may be classed under four heads:
explosive fruits ; transportation by wind; transportation by
birds ; burs.
FIG. 250.— EXPLOSIVE
FRUITS OF OXALIS.
An exploding pod is shown
at c. The dehiscence is
FIG. 249.—~ EXPLOSION OF shown at 2, The structure
THE BALSAM POD. of the pod is seen at a.
Explosive Fruits. — Some pods open with explosive force
and discharge the seeds. Even beans and everlasting peas
do this. More marked examples are the locust, witch
hazel, garden balsam (Fig. 249), wild jewel-weed or impa-
tiens (touch-me-not), violet, crane’s-bill or wild geranium,
bull nettle, morning glory, and the oxalis (Fig. 250). The
(72
DISPERSAL OF SEEDS 173
oxalis is common in several species in the wild and in
cultivation. One of them is known as wood sorrel. Figure
250 shows the common yellow oxalis. The pod opens
loculicidaily. The elastic tissue suddenly contracts when
dehiscence takes place, and the seeds are thrown violently.
The squirting cucumber is easily grown in a garden (pro-
cure seeds of seedsmen), and the fruits discharge the seeds
with great force, throwing them many
feet.
Wind Travelers. — Wind - transported
seeds are of two general kinds: those
that are provided with wings, as the flat
seeds of catalpa (Fig. 251) and cone-bear-
ing trees and the samaras of ash, elm,
tulip-tree, ailanthus, and maple; and
those which have feathery buoys or para-
chutes to enable them to float in the air.
Of the latter kind are the fruits of many
composites, in which the pappus_ is
copious and soft. Dandelion and thistle
are examples. The silk of the milkweed
and probably the hairs on the cotton seed
have a similar office, and also the wool of
the cat-tail. Recall the cottony seeds of Fic. 251. — WincED
the willow and the poplar. tae pe aba
Dispersat by Birds. — Seeds of berries and of other
small fleshy fruits are carried far and wide by birds. The
pulp is digested, but the seeds are not injured. Note how
the cherries, raspberries, blackberries, June-berries, and
others spring up in the fence rows, where the birds rest.
Some berries and drupes persist far into winter, when they
supply food to cedar birds, robins, and the winter birds.
Red cedar is distributed by birds. Many of these pulpy
174 BEGINNERS’ BOTANY
fruits are agreeable as human food, and some of them
have been greatly enlarged or “improved ” by the arts of
the cultivator. The seeds are usually indigestible.
Burs.— Many seeds and fruits bear spines, hooks, and
hairs, which adhere to the coats of animals and to clothing.
The burdock has an involucre with hooked scales, contain-
ing the fruits inside. The clotbur is also an involucre.
Both are composite plants, allied to thistles, but the
whole head, rather than the separate
fruits, is transported. In some com-
posite fruits the pappus takes the
form of hooks and spines, as in the
“Spanish bayonets” and “ pitch-
forks.”’ Fruits of various kinds are
known as “stick tights,’ as of the
agrimony and hound’s-tongue. Those
who walk in the woods in late sum-
mer and fall are aware
that plants have means
of disseminating them-
selves (Fig. 252). Ifit
is impossible to iden-
tify the burs which one
finds on clothing, the seeds may be planted and specimens
of the plant may then be grown.
FIG. 252.—STEALING A RIDE.
SUGGESTIONS. —174. What advantage is it to the plant to have
its seeds widely dispersed? 175. What are the leading ways in
which fruits and seeds are dispersed? 176. Name some explosive
fruits. 177. Describe wind travelers. 178. What seeds are car-
ried by birds? 179. Describe some bur with which you are
familiar. 180. Are adhesive fruits usually dehiscent or indehis-
cent? 181. Do samaras grow on low or tall plants, as a rule?
182. Are the cotton fibres on the seed or on the fruit? 183.
Name the ways in which the common weeds of your region are
disseminated. 184. This lesson will suggest other ways in which
DISPERSAL OF SEEDS a YA
seeds are transported. Nuts are buried by squirrels for food ; but
if they are not eaten, they may grow. ‘The seeds of many plants
are blown on the snow. ‘The old stalks of weeds, standing through
the winter, may serve to disseminate the plant. Seeds are carried
by water down the streams and along shores. About woollen mills
strange plants often spring up from seed brought in the fleeces.
Sometimes the entire plant is rolled for miles before the winds.
Such plants are “tumbleweeds.”” Examples are Russian thistle,
hair grass or tumblegrass (fanicum capillare), cyclone plant
(Cycloloma platyphyllum), and white amaranth (Amarantus
albus). About seaports strange plants are often found, having
been introduced in the earth that is used in ships for ballast.
These plants are usually known as “ ballast plants.” Most of them
do not persist long. 185. Plants are able to spread themselves by
means of the great numbers of seeds that they produce. How
many seeds may a given elm tree or apple tree or raspberry bush
produce ?
FIG, 253.— THE FRUITS
OF THE CAT-TAIL ARE
LOOSENED BY WIND
AND WEATHER.
CHAPTER XXIII
PHENOGAMS AND CRYPTOGAMS
THE plants thus far studied produce flowers; and the
flowers produce seeds by means of which the plant is prop-
FIG. 254.— CHRISTMAS FERN.
— Dryopteris acrostichoides; and sometimes are not visible to
known also as Aspidium.
Prominent among the _ spore-
propagated plants are ferns. The
agated. There are other plants,
however, that produce no seeds,
and these plants (including bac-
teria) are probably more numer-
ous than the seed-bearing plants.
These plants propagate by means
of spores, whichare generative cells,
usually simple, containing no em-
bryo. These spores are very small,
the naked eye. b
common Christmas fern (so called
because it remains green during
winter) is shown in Fig. 254. The
plant has no trunk. The leaves
spring directly from the ground.
The leaves of ferns are called
fronds. They vary in shape, as
other leaves do. Some of the
fronds in Fig. 254 are seen to be
narrower at the top. If these are
examined more closely (Fig. 255),
176
Fic. 255. — FRUITING FRonD
OF CHRISTMAS FERN.
Sori at a. One sorus with its in-
dusium at 4. =
PHENOGAMS AND CRYPTOGAMS r77
it will be seen that the leaflets are contracted and are
densely covered beneath with brown bodies. These bodies
are collections of sporangia or spore-cases.
FIG. 257.—SORI AND Spo-
RANGIUM OF POLYPODE.
A chain of cells lies along
the top of the sporangium,
which springs back elasti-
FIG. 256.—COMMON POLYPODE FERN. cally on drying, thus dis-
Polypodium vulgare.
seminating the spores,
The sporangia are collected into little groups, known as
sori (singular, sorus) or fruit-dots. Each sorus is covered
with a thin scale or shield, known as
an indusium. This indusium sepa-
rates from the frond at its edges, and
the sporangia are exposed. Not all
ferns have indusia. The polypode
FIG. 258. — THE BRAKE
FRUITS UNDERNEATH
(Figs. 256, 257) does not; the sori THE REVOLUTE
are naked. In the brake (Fig. 258) pee
FIG. 259.— FRUITING PINNULES
OF MAIDENHAIR FERN.
N
and maidenhair (Fig. 259) the
edge of the frond turns over
and forms an indusium. The
nephrolepis or sword fern of
greenhouses is allied to the
polypode. The sori are in a
single row on either side the
midrib (Fig. 260). The indu-
sium is circular or kidney-
shaped and open at one edge
178 BEGINNERS’ BOTANY
FIG. 260.— PART OF FROND OF
SworD FERN. To the pupil: Is
this illustration right side up ?
or finally all around. The
Boston fern, Washington fern,
Pierson fern, and others, are
horticultural forms of the
common sword fern. In some
ferns (Fig. 261) an entire
frond becomes contracted to
cover the sporangia.
The sporangium or spore-case of a fern is a more or less
globular body and usually with a stalk (Fig. 257). /¢ con-
tains the spores. When ripe it
bursts and the spores are set free.
In a moist, warm place ¢he spores
germinate. They produce a small,
flat, thin, green, more or less heart-
shaped membrane (Fig. 262). This
is the prothallus. Sometimes the
prothallus is an inch or more across,
but oftener it is less than a ten cent
piece in size, Although easily
FIG. 262.— PROTHALLUS OF A
FERN. Enlarged:
Archegonia at @ ; antheridia at 3,
sree FIG. 261, FERTILE AND
seen, it 1S commonly unknown ex- STERILE FRONDS OF THE
cept to botanists. Prothalli may Sd SCENES USE
often be:found in greenhouses where ferns are grown.
Look on the moist stone or
brick walls, or on the firm soil
of undisturbed pots and beds;
or spores may be sown in a
damp, warm place.
On the under side of the
prothallus two kinds of organs
are borne.. ‘These ““arery the
archegonium (containing egg-
cells)and the antheridium (con-
&
PHENOGAMS AND CRYPTOGAMS 179
taining sperm-cells). These organs are minute specialized
parts of the prothallus. Their positions on a particular
prothallus are shown at a and @ in Fig. 262, but in some
ferns they are on separate prothalli (plant dioecious). Ze
sperm-cells escape from the antheridium and in the water
that collects on the prothallus are carried to the archegonium,
where fertilization of the egg takes place. Yrom the ferti-
lized egg-cell a plant grows, becoming a “fern.” In
most cases the prothallus soon dies. The prothallus is the
gametophyte (from Greek, signifying the fertilized plant).
The fern plant, arising from the fertilized egg in the
archegonium, becomes a perennial plant, each year pro-
ducing spores from its fronds (called the sporophyte) ; but
these spores— which are merely detached special kinds of
cells — produce the prothallic phase of the fern plant,
from which new individuals arise. A fern zs fertilized but
once in its lifetime. The “fern” bears the spore, the
spore gives rise to the prothallus, and the egg-cell of the
prothallus (when fertilized) gives rise to the fern.
A similar alternation of generations runs all through the
vegetable kingdom, although there are some groups. of
plants in which it is very obscure or apparently wanting.
It is very marked in ferns and mosses. In alge (includ-
ing the seaweeds) the gametophyte is the “plant,” as
the non-botanist knows it, and the sporophyte is incon-
spicuous. Thereis a general tendency, in the evolution of
the vegetable kingdom, for the gametophyte to lose its rela-
tive importance and for the sporophyte to become larger and
more highly developed. In the seed-bearing plants the
sporophyte generation is the only one seen by the non-
botanist. The gametophyte stage is of short duration and
the parts are small; it is confined to the time of fertiliza.
tion.
180 BEGINNERS’ BOTANY
The sporophyte of seed plants, or the “plant” as we
know it, produces two kinds of spores -— one kind becom-
ing pollen-grains and the other kind embryo-sacs. The
pollen-spores are borne in sporangia, which are united into
what are called anthers. The embryo-sac, which contains
the egg-cell, is borne in a sporangium known as an ovule.
A gametophytic stage ts present in both pollen and embryo
sac: fertilization takes place, and a sporophyte arises. Soon
this sporophyte becomes dormant, and is then known as an
embryo. The embryo is packed away within tight-fitting
coats, and the entire body is the seed. When the condi-
tions are right the seed grows, and the sporophyte grows
into herb, bush, or tree. The utility of the alternation of
generations is not understood. |
The spores of ferns are borne on leaves; the spores of
seed-bearing plants are also borne amongst a mass of
specially developed conspicuous leaves known as flowers;
therefore these plants have been known as the flowering
plants. Some of the leaves are developed as envelopes
(calyx, corolla), and others as spore-bearing parts, or spo-
rophylls(stamens, pistils). But the spores of the lower
plants, as of ferns and mosses, may also be borne in spe-
cially developed foliage, so that the line of demarcation
between flowering plants and flowerless plants is not so
definite as was once supposed. The one definite distinction
between these two classes of plants is the fact that ove class
produces seeds and the other does not. The seed-plants are
now often called spermaphytes, but there is no single
coordinate term to set off those which do not bear seeds.
It is quite as well, for popular purposes, to use the terms
phenogams for the seed-bearing plants and cryptogams for
the others. These terms have been objected to in recent
years because their etymology does not express literal facts
PHENOGAMS AND CRYPTOGAMS 181
(phenogam signifying “showy flowers,” and cryptogam
“hidden flowers’), but the terms represent distinct ideas
in classification. The cryptogams include three great
series of plants—the Thallophytes or alge, lichens, and
fungi; the Bryophytes or mosslike plants; the Pteridophytes
or fernlike plants.
SUGGESTIONS. —186. Zhe parts of a fern leaf. The primary
complete divisions of a frond are called pinnz, no matter whether
the frond is pinnate or not. In
ferns the word “pinna”’ is used in
essentially the same way that leaf-
let is in the once-compound leaves
of other plants. The secondary
leaflets are called pinnules, and in
thrice, or more, compound fronds,
the last complete parts or leaflets
are ultimate pinnules. The dia-
gram (Fig. 263) will aid in making
the subject clear. If the frond
were not divided to the midrib, it
would be simple, but this diagram
represents a compound frond.
The general outline of the frond,
as bounded by the dotted line, is
ovate. The stipe is very short.
The midrib of a compound frond
is known as the rachis. In a de-
compound frond, this main rachis
is called the primary rachis. Seg- pig. 263.— DIAGRAM TO EXPLAIN
ments (not divided to the rachis) Mee TB IOLOG “OE. ae
are seen at the tip, and down to FROND,
f# on one side and to m on the
other. Pinne are shown at 7,%, 2,0, . The pinna a is entire ;
m is crenate-dentate ; zis sinuate or wavy, with an auricle at the
base ; & and Zare compound. ‘The pinna & has twelve entire pin-
nules. (Is there ever an even number of pinnules on any pinna?)
Pinna 7 has nine compound pinnules, each bearing several entire
ultimate pinnules. Zhe spores. —187. Lay a mature fruiting frond
of any fern on white paper, top side up, and allow it to remain in
a dry, warm place. The spores will discharge on the paper.
188. Lay the full-grown (but not dry) cap of a mushroom or
toadstool bottom down on a sheet of clean paper, under a venti-
lated box in a warm, dry place, A day later raise the cap.
CHAPTER XXIV
STUDIES IN CRYPTOGAMS
TuE pupil who has acquired skill in the use of the com-
pound microscope may desire to make more extended ex-
cursions into the cryptogamous orders. The following
plants have been chosen as examples in various groups.
Ferns are sufficiently discussed in the preceding chapter.
BACTERIA
If an infusion of ordinary hay is made in water and allowed to
stand, it becomes turbid or cloudy after a few days, and a drop
under the microscope will show the presence of minute oblong
cells swimming in the water. perhaps by means of numerous hair-
like’ appendages, that project through the cell wall from the pro-
toplasm within. At the surface of the dish containing the infusion
the cells are non-motile and are united in long chains. Each
of these cells or organisms is a bacterium (plural, bacteria).
(Fig. 135-)
Bacteria are very minute organisms,—the smallest known —
consisting either of separate oblong or spherical cells, or of
chains, plates, or groups of such cells, depending on the kind.
They possess a membrane-like wall which, unlike the cell walls of
higher plants, contains nitrogen. ‘The presence of a nucleus has
not been definitely demonstrated. Multiplication is by the fission
of the vegetative cells ; but under certain conditions of drought,
cold, or exhaustion of the nutrient medium, the protoplasm of the
ordinary cells may become invested with a thick wall, thus form-
ing an endospore which is very resistant to extremes of environ-
ment. No sexual reproduction is known.
Bacteria are very widely distributed as parasites and sapro-
phytes in almost all conceivable places. Decay is largely caused
by bacteria, accompanied in animal tissue by the liberation of
foul-smelling gases. Certain species grow in the reservoirs and
pipes of water supplies, rendering the water brackish and often
undrinkable. Some kinds of fermentation (the breaking down or
decomposing of organic compounds, usually accompanied by the
182
STUDIES IN CRYPTOGAMS 183
formation of gas) are due to these organisms. Other bacteria
oxidize alcohol to acetic acid, and produce lactic acid in milk and
butyric acid in butter. Bacteria live in the mouth, the stomach, the
intestines, and on the surface of the skins of animals. Some secrete
gelatinous sheaths around themselves; others secrete sulphur or
iron, giving the substratum a vivid eclour,
Were it not for bacteria, man could not live on the earth, for
not only are they agents in the process of decay, but they are
concerned in certain healthful processes of plants and animals.
We have learned in Chapter VIII how bacteria are related to nitro-
gen-gathering.
Bacteria are of economic importance not alone because of their
effect on materials used by man, but also because of the dsease-
producing power of certain species. ws is caused by a spherical
form, ¢efanus or lock-jaw by a rod-shaped form, diphtheria by
short oblong chains, ¢aberculosts or “ consumption” by more slen-
der oblong chains, and “typhoid fever, cholera, and other diseases
by other forms. Many diseases of animals and plants are
caused by bacteria. Disease-producing bacteria are said to be
pathogenic.
The ability to grow in other nutrient substances than the natu-
ral one has greatly facilitated the study of these minute forms
of life. By the use of suitable culture media and proper precau-
tions, pure cultures of a particular disease-producing bacterium
may be obtained with which further experiments may be con-
ducted.
Milk provides an excellent collecting place for bacteria coming
from the air, from the coat of the cow and from the milker. Dis-
ease germs are sometimes carried in milk. If a drop of milk is
spread on a culture medium (as agar), and provided with proper
temperature, the bacteria will multiply, each one forming a colony
visible to the naked eye. In this way, the number of bacteria
originally contained in the milk may be counted.
Bacteria are disseminated in water, as the germ of typhoid fever
and cholera; in milk and other fluids; in the air; and on the
bodies of flies, feet of birds, and otherwise.
Bacteria are thought by many to have descended from algze by
the loss of chlorophyll and: decrease in size due to the more
specialized acquired saprophytic and parasitic habit.
ALG
The alge comprise most of the green floating “ scum” which
covers the surfaces of ponds and other quiet waters. ‘The masses
of plants are often called “ frog spittle.” Others are attached to
stones, pieces of wood, and other objects submerged in streams
184 BEGINNERS’? BOTANY
and lakes, and many are found on moist ground and on dripping
rocks. Aside from these, all the plants commonly known as seaweeds
belong to this category ; these latter are inhabitants of salt water.
The simplest forms of alge consist of a single spherical cell,
which multiplies by repeated division or fission. Many of the
forms found in fresh water are filamentous, ze. the plant body
consists of long threads, either simple or branched. Such a plant
body is termed a “tadlus. ‘This term applies to the vegetative
body of all plants that are not differentiated into stem and leaves.
Such plants are known as ¢hadlophy/es (p. 181). All algee contain
chlorophyll, and are able to assimilate carbon dioxide from the air.
This distinguishes them from the fungi.
LVostoc. —On wet rocks and damp soil dark, semitransparent
irregular or spherical gelatinous masses about the size of a pea are
often found. These consist of a colony of contorted filamentous
algee embedded in the jelly-like mass. The chain of cells in the
filament is necklace-like. Each cell is homogeneous, without
apparent nucleus, and blue-green in colour, except one cell which
is larger and clearer than the rest. ‘The plant therefore belongs
to the group of d/ue-green alee. The jelly probably serves to
maintain a more even moisture and to provide mechanical protec-
tion. Multiplication is wholly by the breaking
up of the threads. Occasionally certain cells
of the filament thicken to become vesting-
spores, but no other spore formation occurs.
Oscillatoria. —The blue-green coatings
found on damp soil and in water frequently
show under the microscope the presence of
filamentous algee composed of many short
FIG, 264.—FILAMENT OF OSCILLATORIA, showing one
dead cell where the strand will break.
FIG. 265. — STRAND
OF SPIROGYRA,
showing the chlo-
homogeneous cells (Fig. 264). If watched
closely, some filaments will be seen to wave
back and forth slowly, showing a peculiar power
of movement characteristic of this plant.
Multiplication is by the breaking up of the
threads. There is no true spore formation.
Spirogyra. — One of the most common forms
of the green algz is spirogyra (Fig. 265). This
rophyll bands.
There is a nu-
cleus ata. How
many cells, or
parts of cells, are
shown in this fig-
ure ?
STUDIES IN CRYPTOGAMS 185
plant often forms the greater part of the floating green mass (or
“ frog spittle”) on ponds. The threadlike character of the thallus
can be seen with the naked eye or with a hand
lens, but to study it carefully a microscope
magnifying two hundred diameters or more
must be used. The thread is divided into long
cells by cross walls which, according to the
species, are either straight or curiously folded
(Fig. 266). The chlorophyll is arranged in
beautiful spiral bands near the wall of each cell.
From the character of these bands the plant
takes its name. Each cell is provided with a
nucleus and other profoplasm. ‘The nucleus is
suspended near the centre of the cell (a, Fig.
265) by delicate strands of protoplasm radiat-
ing toward the wall and terminating at certain
points in the chlorophyll band. The remainder
of the protoplasm forms a thin layer lining the
wall. The interior of the cell is filled with
cell-sap. The protoplasm and nucleus cannot FIG. 266.-—Con-
be easily seen, but if the plant is stained with INGATION: (OR
a dilute alcoholic solution of eosine they become Se ea
clear: Ripe zygospores
: 3 < on the left; a,
Spirogyra is propagated vegetatively by the Sbainecuine
breaking off of parts of the threads, which con- tubes"
tinue to grow as new plants. Resting-spores,
which may remain dormant for a time, are formed by a process
known as comjugation. ‘Two threads lying side
by side send out short projections, usually from
all the cells of a long series (Fig. 266). The
projections or processes from opposite cells
grow toward each other, meet, and fuse, form-
ing a connecting tube between the cells. The
protoplasm, nucleus, and chlorophyll band of
one cell now pass through this tube, and unite
with the contents of the other cell. ‘The en-
tire mass then becomes surrounded by a thick
cellulose wall, thus completing the vest#ng-
spore, or zygospore (2, Fig. 266).
Zygnema is an alga closely related to spiro-
Ret Ssianp co and found in similar places. Its life
oR FILAMENT op -Distory is practically the same, but it differs
ZYGNEMA, freed {fom spirogyra in having ‘wo star-shaped
from its gelatinous Chlorophyll bodies (Fig. 267) in each cell, in-
covering. stead of a chlorophyll-bearing spiral band.
186 BEGINNERS’ BOTANY
Vaucheria is another alga common in shallow water and on
damp soil. The thallus is much branched, but the threads are
not divided by cross walls.as in spirogyra. ‘The plants are attached
by means. of colourless root-like organs which are much like the
root hairs of the higher plants: these are vAzzo/ds. ‘The chloro-
phyll is in the form of grains scattered through the thread.
Vaucheria has a special mode of asexual reproduction by
means of swimming spores or swarvm-spores. ‘These are formed
singly in a short enlarged lateral branch known as the sporangium.
When the sporangium bursts, the entire contents escape, forming
a single large swarm-spore, which swims about by means of
numerous.lashes or cilia on its surface. The swarm spores are so
large that they can be seen with the naked eve. After swimming
about for some time they come to rest and germinate, producing
a new plant.
The formation of resting-spores of vaucheria is acomplished by
means of special organs, odgonia (0, Fig. 268) and antheridia
(a; Big: 268). These
are both specially devel-
oped branches from the
thallus. The antheridia
are nearly cylindrical, and
curved toward the odgonia.
The upper part of an an-
theridium is cut off by a
cross wall, and within it
numerous ciliated spevm-cells are formed. These escape by the
ruptured apex of the antheridium. ‘The odgonia are more en-
larged than the antheridia, and have a beak-like projection turned
a little to one side of the apex. They are separated from the
thallus thread by a cross wall, and contain a single large green
cell, the ege-ce/7. The apex of the odgonium is dissolved, and
through the opening the sperm-cells enter. Fertilization is thus
accomplished. After fertilization the egg-cell becomes invested
with a thick wall and is thus converted into a resting-spore, the
oo0spore.
FIG. 268. — THREAD OF VAUCHERIA WITH
OOGONIA AND ANTHERIDIA.
fucus. — These are rather large specialized algz belonging to the
group known as brown seaweeds and found attached by a disk to
the rocks of the seashore just below high tide (Fig. 269). They
are firm and strong to resist wave action and are so attached as to
avoid being washed ashore. They are very abundant alge. In
shape the plants are long, branched, and multicellular, with either
flat or terete branches. They are olive-brown. Propagation is by
the breaking off of the branches. No zodspoyes are produced,
as in many other seaweeds ; and reproduction is wholly sexual.
»
STUDIES IN CRYPTOGAMS 187
The antheridia, bearing sperm-cells, and the odgonia, each bearing
eight egg-cells, are sunken in pits or conceptacles. ‘These pits
are aggregated in the swollen lighter coloured tips of some of the
branches (s, s, Fig. 269). The egg-cells and sperm-cells escape
from the pits and fertilization takes place in the water. ‘The
matured eggs, or spores, reproduce the fucus plant directly,
FIG. 269,— Fucus. Fruiting
branches at s,s. On the
stem are two air-bladders. FIG. 270, — NITELLA.
Nitella. — This is a large branched and specialized fresh-water
alga found in tufts attached to the bottom in shallow ponds (Fig.
270). Between the whorls of branches are long ¢éernodes consisting
of a single cylindrical cell, which is one of the-largest cells known in
vegetable tissue. Under the microscope the walls of this cell are
found to be lined with a layer of small stationary chloroplastids,
within which layer the protoplasm, in favourable circumstances,
will be found in motion, moving up one side and down the other
(in rotation). Note the clear streak up the side of the cell and its
relation to the moving current.
FUNGI
Some forms of fungi are familiar to every one. Mushrooms
and toadstools, with their varied forms and colours; are common
in fields, woods, and pastures. {fn every household the common
moulds are familiar intruders, appearing on old bread, vegetables,
and even within tightly sealed fruit jars, where they form a felt-
like layer dusted over with blue, yellow, or black powder. The
strange occurrence of these plants long mystified people, who
188 BEGINNERS’ BOTANY
oht they were productions of the dead matter upon which they
sre, but now we know that a mould, as any other plant, cannot
criginaté spontaneously; it must start from something which is
analogous to a seed. The ‘‘seed’’ is this case is a spore. A spore
may be produced by a vegetative process (growing out from the
ordinary plant tissues), or it may be the result of a fertilization
process.
Favourable conditions for the growth of fungi.—Place a piece
of bread under a moist bell jar anc another in an uncovered
place near by. Sow mould on each. Note the result from day to
day. Moisten a third piece of bread with weak copper sniphate
(blue vitriol) or mercuric chloride solution, |
sow mould, cover with bell jar, note results,
and explain. Expose pieces of different kinds
of food in a damp atmosphere and observe
the variety of organisms appearing. Fungi
are saprophytes or parasites, and must be
provided with organic matter on which to
grow. They are usually most abundant in
moist places and wet seasons.
FIG. 271. — MUCOR Mould.—One of these moulds (Mucor mu-
MUCEDO, showing habit. cedo), which is very common on all