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BEGINNERS' BOTANY
THE MACMILLAN COMPANY
NEW YORK • BOSTON • CHICAGO SAN FRANCISCO
MACMILLAN & CO , Limited
LONDON • BOMBAY • CALCUTTA MELBOURNE
THE MACMILLAN CO. OF CANADA, Ltdw
TORONTO
BOUQUET OF BEARDED WHEAT
BEGINNERS' BOTANY
BY
L. H. BAILEY
AUTHORIZED BY THE MINISTER OF EDUCATION FOR ONTARIO
TORONTO THE MACMILLAN CO. OF CANADA, LIMITED
1921
Copyright, 1921 By the MACMILLAN CO. OF CANADA LTD.
PREFACE
In ail 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 l)ooks. Books will be very useful m 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 v/ith 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.
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 in a shop. "We are begin- ning to learn that the ideals and the abilities should he developed out of the common surroundings and affairs of
PREFACE
VII
life ratlier 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.
CONTENTS
CHAPTER
I. No Two Plants or Parts are Alike
II. The Struggle to Live
III. Survival of the Fit
IV. Plant Societies V. The Plant Body
VI. Seeds and Germination
VII. The Root — The Forms of Roots
VIII. The Root — Function and Structure
IX. The Stem — Kinds and Forms — Pruning
X. The Stem — Its General Structure
XI. Leaves — Form and Position .
XII. Leaves — Structure and Anatomy
XIII. Leaves — Function or Work
XIV. Dependent Plants . XV. Winter and Dormant Buds
XVI. Bud Propagation
XVII. How Plants Climb .
XVIII. The Flower — Its Parts and Forms
XIX. The Flower — Fertilization and Poll
XX. Flower-clusters
XXI. Fruits
XXII, Dispersal of Seeds .
XXIII. Phenogams and Cryptogams
XXIV. Studifis in Cryptogams Index
BEGINNERS' BOTANY
CHAPTER I NO TWO PLANTS OR PARTS ARE ALIKE
Fig. I. — No Two Branches are Alike. (Hemlock.)
If one compares any two plants of 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 sta^tdard type. If one compares any two brandies or twigs on a tree, it will be found that they differ in size, age, form, vigour, and in other ways (Fig. i).
If one compares a7ty tivo leaves, it will be found that they are unlike in size, shape, colour, yeining, 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.
BEGINNERS' BOTANY
If the pupil extends his observation to animals, he will still find the same truth ; for probably no 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
Fig. 2. — No Two Leaves are Alike.
discover the differences, remembering that nothing in 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.
Suggestions. — 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 "suckers' from one root?
(3) Shade or colour.
(4) How many leaves.
(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 per- sonal work by the pupil. Every pupil should handle 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. I 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.
4
THE STRUGGLE TO LIVE
5
The plant meets its conditions by succtmibing to them (that is, by dying), or by adapting itself 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.
Fig. 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. The organism adapts itself to its eiivironmcnt, or else it weakens or dies- 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? TIoav does the florist reduce competition to its lowest terms? what is the result?
CHAPTER III
THE SURVIVAL OF THE FIT
The plants that most perfectly meet their conditions are able to persist. They perpetuate themselves. Their off- spring are likely to inherit some of the attributes that enabled them successfully to meet the battle of life. The fit (those best adapted to their conditions) tend to survive.
Adaptation to conditions depends on the fact of varia- tion; that is, if plants were perfectly rigid or invariable (all exactly aUke) they could not meet new conditions. Conditions are necessarily new for every organism. It is impossible to picture a perfectly inflexible and stable succes- sion of plants or animals.
Breeding. — Man is able to modify plants and animals. A.11 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- berry with the wild form.
By choosing seeds from a plant that pleases him, the breeder may be able, under given conditions, to produce
7
Fig. 5. — Desirable and Undesirable Types of Cotton Plants. Why?
BEGINNERS' BOTANY
Fig. 6, — Flax Breeding.
A '.s a plant grown for seed production
/; f'i.r lil.iv iinMlur.tioii. Wl'.y?
Suggestions. • — 6. Every pu- pil should un- dertake at least one simple ex- periment in se- lection of s6ed. 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 cars 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 bre(>dinfT.
numbers of plants with more or less of the desired quali- ties; from the best of these, he may again choose ; and so on 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- tion. A some- what similar process pro- ceeds in wild nature, and it is then known as natural se- lection.
Fig. 7. — Breed- ing.
A, effect from breed- ing from smallest grains (after four years), average head; B, result from breeding from the plumpest and heaviest grains (after four years), average head.
CHAPTER IV PLANT SOCIETIES
In the long course of time in which plants have been accommodating themselves to the varying conditions in which they are obHged to grow, tJiey 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-7'egion societies^ comprising aquatic and bog vegetation (Fig. 8); arid-region societies ^ comprising desert and most sand-region vegetation ; mid-region societies^ 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 leaves, 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 tropical societies^ temperate-region societies^ boreal or cold-region societies.
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BEGINNERS' BOTANY
With reference to altitude, societies might be classified as lowland (which are chiefly wet-region), intennediaie (chiefly mid-region), stibalpijie or mid-moimtam (which are chiefly boreal), alpine or high-moimtain.
The above classifications have reference chiefly to great geographical floras or societies. But there are societies within societies. There are small societies coming within the experience of every person who has ever seen plants
Fig. 8. — a Wet-region Society.
growing in natural conditions. There are roadside, fence- row, lawn, thicket, pasture, dune, woods, cliff, barn-yard societies. Every different place has its characteristic vegeta- tion. Note the smaller societies in Figs. 8 and 9. 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 iiitermingled plants^ or of dense chimps 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 ^n-/ 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 intei^mingled 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 grvwing side by side ; by groiving above or beneath. In sparsely popu- lated societies, plants may grow alongside each other. In most cases, however, there is overgrowth and undergrowth: 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
Fig. io. — Overgrowth and Undergrowth in Three Series, — trees, bushes, grass.
PLANT SOCIETIES 1 3
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 BEGTNNEJiS' 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 to the plant. Autumn colours are not caused hy 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 cccology 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 lo or 20 ft. square — for special study. He should make a list showing (i) 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 pupil should endoavour 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 root, stem, leaf, flower, fruit, and seed. Familiar plants differ wonderfully ift size a7td sJiape, — 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, diXidi 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, ii 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 bears only root-branches. The stem, however, bears leaves, flowers, and fruits. Those Hving 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 tozvard light
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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. TJie flowers always preeede 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 foliage. 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- braces various stages, or epochs, as dormant seed, gerin ination, grow thy flowering, fruiting. Some plan ts 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 the young seed, not with germi-
j&R. vt. — Plant of a Vhitib Sunflower.
Fig. 12— Frame- work OF Fig. h.
THE PLANT BODY 1/
nation. // 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
I8
BEGINNERS' BOTANY
is, jalse 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 clhnate by being killed by frosty 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-
Fig. 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 and a more or less elevated head are trees (Fig. 14). All shrubs and trees are perennial. Every plant makes an effort
to propagate^ or to perpetuate its :^-^i^'$4 kind ; and, as far as we can Biff^f; see, this is the end for which the plant itself lives. The seed or spore is the final product of the plaftt.
Fig. 14. — a Tree. birch.
The weeping
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 th€ 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 miniature 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 — OF THE Bean, comprising half of the bean — is shown at /?, cotyledon; <7, R. The cauliclc is at O, The plumule is mutf i^'fim shown at A, The cotyledons are attached nod*- to the caulicle at F: this point may be taken
as the first node or joint.
The Number of Seed-leaves. — All plants having two 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 one 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 halves 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 AXD GEI:MI NATION 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 \^ provided zvith food \o support the germinat- ing plant. Commonly this food is starch. The food may be stored in the cotyledons^ as in bean, pea, squash ; or out- side the cotyledojiSf 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 fig.i6.— exter- the pollen-tube entered the forming ovule nal parts op and through which the caulicle breaks in germination. The micropyle is shown at M in Fig. i6. 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. i6. 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.
22 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 {air\ it 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 its elf y germination is 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 respires freely, throwing off carbon dioxide (COo).
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. The general direc- tion of the young hypocotyl^ 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
Fig. 17. — Pea. Grotesque forms assumed when the roots cannot gain entrance to the soil.
air, germination is said to be epigeal (" above the earth "). Bean and pumpkin are examples. When the hypocotyl does not elongate greatly and the cotyledons remain under ground, the germin- ation is hypogeal (''be- neath the earth"). Pea and scarlet runner bean are examples (Fig. 48). When the germinating seed lies on a hard sur- face, as on closely com- 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 plumule- 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- pocotyl, or elongated caulicle, emerges, the plumule-leaves have begun to en- large, and to unfold (Fig. 18). The hypocotyl elongates rapidly. One end of it is held by the roots. The other is held by the seed-coats in the soil. 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,
Fig. 18. — Cotyledons OF Germinating Bean spread apart
TO SHOW ELONGAT-
ING Caulicle and Plumule.
M
BEGINNEKS* BOTAMY
and the plant straightens and the cotyledons expand. These coty- ledons, or " halves of the bean," persist for some time {by 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.
Germination of Castor 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 greatly elongates. On examining germin- ating seed, however, it will be found that the cotyledons are contained inside a fleshy body, or sac {a, Fig. 2 1 ). This sac is the endosperm. Against its inner surface the thin, veiny coty- ledons are very closely pressed, ab-
FiG. 19. — Germination of Bean.
Fig. 20. — Sprout^ ING OF Castor Bean.
Fig. 21.— Germina- tion OF Castor Bean.
Endosperm at a.
Fig. 22. — Castor Bean.
Endosperm at a,n\ coty- ledons at b.
Fig. 23. — Germination Complete in Castor 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. 24. — Sprout- ing Indian Corn.
Hilum at h; micro* pyle at d.
Fig. 25. — Kernel OF Indian Corn.
Caulicle at b; cotyle- don at a; plumule at/.
Fig. 26.— Indian Corn.
Caulicle at c, roots emerging at ni; plumule at/.
single cotyledon is at ^, the caulicle at b, the plumule at/. 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 (/, 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 ^ yr epicotyl elongates, particularly if 'Vfj^ the seed is planted
deep or if it is kept for a time confined. In Fig. 27 the epicotyl has elongated from n to p. The true plumule-leaf is at o, but other leaves grow from its sheath. In Fig. 28 the roots are seen emerging from the two ends of the caulicle-
Fig. 27. — Indian Corn.
o, plumule; n to/, epicotyl.
26
BEGINNERS' BOTANY
sheath, r, m ; the epicotyl has grown to / ; the first plu- mule-leaf is at o.
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 in number .-' 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 pine cone and draw it and the seeds as they lie in place 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-
FiG. 28. — Germination is Com
PLETE.
/, top of epicotyl ; o, plumule-leaf; m, roots; c, lower roots.
SEEDS AND GERMINATION'
n
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 "i
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 before the study is taken up, put seeds to soak in moss or cloth. The pupil 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
Fig. 29. — Cones of Hem- lock (above), White Pine, Pitch Pine.
28
BEGINNEL'S' BOTANV
case-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- Bate 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, <i 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 vrarm 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. Ifi oir necessary for tJie germination and grorvth 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 -v^-ith 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.
HEEBS AND GERMINATION ^^
preceding experiment. 17- What is the nature of the gas given off by germinating seeds F 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 ivhat 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 darTcness 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 c"hange that takes place beneath it. 22. Seedling of jtine- 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 w^ood 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 before the cones? 23. Home experiments. If desired, nearly all of the fore-
30 BEGINNEBS' BOTANY
going experiments may be tried at home. The pupil can thus make the drawings for the notebook at home- A daily record of measure- ments of the change in size of the various parts of the seedliiig should also be made. 24. Seed-testing. — It is important that one know before planting whether seeds are good, or able to grow. A simple seed-tester may be made of two plates, one inverted over the other (Fig. 31). The lower plate is nearly filled with clean sand, which is covered with cheese cloth or blot- ting paper on which the seeds are placed. Canton flannel is sometimes used in place, of sand and blotting paper. The seeds are then covered with another blotter or piece of cloth, and water is applied until the sand and papers are saturated. Cover with the second plate. Set the plates where they will have about the temperature that the Fig. 31. — a Home-made given seeds would require out of doors, or Seed-tester. perhaps a slightly higher temperature.
Place 100 or more grains of clover, corn, wheat, oats, rye, rice, buckwheat, or other seeds in the tester, and keep record of the number that sprout. The result will give a per- centage measure of the ability of the seeds to grow. Note whether all the seeds sprout with equal vigour and rapidity. Most seeds will sprout in a week or less. Usually such a tester must have fresh sand and paper after each test, for mould fungi are likely to breed in it. If canton flannel is used, it may be boiled. If possible, the seeds should not touch one another.
Note to Teacher. — With the study of germination, the pupil will need to begin dissecting.
For dissecting, one needs a lens for the examination of the smaller parts of plants and animals. It is best to have the lens- mounted on a frame, so that the pupil has both hands free for pulling the part in pieces. An ordinary pocket lens may be mount- ed on a wire in a block as in Fig. A. A cork is slipped on the top of the wire to avoid injury to the face. The pupil should be provided with two dissecting needles (Fig. B), made by securing an ordinary needle in a pencil-like stick. Another convenient ar- rangement is shown in Fig. C. A small tin dish is used for the base. Into this a stiff wire standard is soldered. The dish is filled with solder to make it heavy and firm. Into a cork slipped on the standard, a cross wire is inserted, holding on the end a jeweller's
SEEDS AND GERMINATION
31
glass.* The lens can be moved up and down and sidewise. This outfit can be made for about seventy-five cents. Fig. D shows a convenient hand-rest or uissecting-stand to be used under this lens. It may be 16 in. long, 4 in. high, and 4 or 5 in. broad.
Various kinds of dissecting microscopes are on the market, and these are to be recommended when they can be afforded.
A— Dissecting Stand.
5. — Dis- secting Needle % natural si2e.
C — Dissecting Glass.
^. — Improvised Stand for Lens,
Instructions for the use of the compound microscope, with which some schools may be equipped, cannot be given in a brief space; the technique requires careful training. Such microscopes are not needed unless the pupil studies cells and tissues.
CHAPTER VII
THE ROOT — THE FORMS OF ROOTS
The Root System. — The offices of the root are to hold the plant in place, and to gather food. Not all the food materials, however, are gathered by the roots.
Fig. 32. — Tap-root System of Alfalfa.
Tap-root of the Dandelion.
Fig. 33.
The entire mass of roots of any plant is called its root system. The root system may be annual, biennial or peren- nial, herbaceous or woody, deep or shallow, large or small.
Kinds of Roots. — A strong leading central root, which runs directly downwards, is a tap-root The tap-root forms
THE ROOT— THE FORMS OF ROOTS
33
an axis from which the side roots may branch. The side or spreading roots are usually smaller. Plants that have such a root system are said to be tap-rooted. Examples are red clover, alfalfa, beet, turnip, radish, burdock, dandelion, hickory (Figs. 32, 33).
A fibrous root system is one that is composed of many nearly equal slender branches. The greater number of plants have fibrous roots. Examples are many common grasses, wheat, oats, corn. The buttercup in Fig. 34 has a fibrous root system. Many trees have a strong tap-root when very young, but after a while it ceases to ex- tend strongly and the side roots develop until finally the tap-root character disappears.
Shape and Extent of the Root Sys- tem. — The depth to which roots extend depends on the kind of plant, and the natJire of the soil. Of most plants the roots extend far in all-directions and lie comparatively near the surface. The roots usually radiate from a common point just beneath the surface of the ground.
The roots grow here and there in search of foody often extending much farther in all directions than the spread of the top of the plant. Roots tend to spread farther in poor soil than in rich soil, for the same size of plant. The root has no such defi^iite form as the stem has. Roots are usually very crooked, because they are constantly turned aside by obstacles. Examine roots in stony soil.
Fig. 34. — a Buttercup Plant, with fibrous roots.
34
BEGINNERS* BOTANY
The extent of root surface is usually very large, for the feeding roots are fine and very numerous. An ordinary plant of Indian corn may have a total length of root (measured as if the roots were placed end to end) of several hundred feet.
The fine feeding roots are most abundant in the richest part of the soil. They are attracted by the food materials. Roots often will completely surround a bone or other morsel. When roots of trees are exposed, observe that most of them are horizontal and lie near the top of the ground. Some roots, as of willows, extend far in search of water. They often run into wells and drains, and into the margins of creeks and ponds. Grow plants in a long narrow box, in one end of which the soil is kept very dry and in the other moist : observe where the roots grow.
Buttresses. — With the increase in diameter, the upper roots often protrude above the ground and become bracing buttresses. These buttresses are usually largest in trees
which always have been exposed to strong winds (Fig. 35). Because of growth and thickening, the roots elevate part of their diameter, and the washing away of the soil makes them to appear as if having risen out of the ground.
Aerial Roots. — Although roots usually grow underground, there are some that naturally grow above ground. These usually occur on climbing plants, the roots becoming stip- ports or fulfilling the office of tendrils. These aerial roots usually turn away from the light, and therefore enter the
^a5s^^
Fig. 35. — The Bracing Base of a Field Pine.
THE ROOT— THE EORMS OF ROOTS
35
crevices and dark places of the wall or tree over which the
plant
climbs.
The trumpet creeper (Fig. 36), true or English ivy, and poison ivy climb by means of roots.
Fig. 37. — Aerial Roots of an Orchid.
In some plants all the roots are aerial ; that is, the plant grows above ground^ and the roots gather food from the air. Such plants usually grow on trees. They are known as epiphytes or air-plants. The most fam- iliar examples are some of the tropi- cal orchids which are grown in glass- houses (Fig. 37). Rootlike organs of dodder and other parasites are discussed in a future chapter.
Fig. 36. — Aerial Roots OF Trumpet Creeper OR Tecoma.
36
BEGINNERS' BOTANY
Some plants bear aerial roots, that may propagate the plant or may act as braces. They are often called prop-roots. The roots of Indian corn are familiar (Fig. 38). Many ficus trees, as the banyan of India, send out roots from their branches ; when these roots reach the ground they take hold and become great trunks, thus spreading the top of the parent tree over large areas. The mangrove tree of the tropics grows along seashores and sends down roots from the over- hanging branches (and from the fruits) into the shallow water, and thereby gradually marches into the sea. The tangled mass behind catch- es the drift, and soil is formed.
Adventitious Roots. — Sometimes roots grow from the stem or other unusual places as the result of some accident to the plant, being located without known method or law. They are called adventitious (chance) roots. Cuttir!igs of the stems of roses, figs, geraniums, and other plants, when planted, send out ad- ventitious roots and form new plants. The ordinary roots, or soil roots, are of course not classed as adventitious roots. The adventitious roots arise on occasion, and not as a normal or regular course in the growth of the plant.
No two roots are alike; that is, they vary among them- selves as stems and leaves do. Eacli JHnd of plant has its
Fig. 38. — Indian Corn, showing the brace roots at 00.
THE ROOT— THE FORMS OF ROOTS
37
own form or habit of root (Fig. 39). Carefully wash awa^ the soil from the roots of any two related plants, as oats and wheat, and note the differences in size, depth, direc- tion, mode of branching, num- ber of fibrils, colour, and other
Fig. 39. — Roots of Bari.ey at A and Corn at B. Carefully trace the differences.
features. The character of the root system often governs the treatment that the farmer should give the soil in which the plant or crop grows.
Roots differ not only in their form and habit, but also in colour of tissue, character of bark or rind, and other fea- tures. It is excellent practice to fry to identify different plants by means of their roots. Let each pupil bring to school two plants with the roots very carefully dug up, as cotton, corn, potato, bean, wheat, rye, timothy, pumpkin, clover, sweet pea, raspberry, strawberry, or other common plants.
Root Systems of Weeds. — Some weeds are pestiferous because they seed abundantly, and others because their underground parts run deep or far and are persistent. Make out the root systems in the six worst weeds in your locality.
CHAPTER VIII
THE ROOT. — FUNCTION AND STRUCTURE
The function of roots is twofold, — to provide support or anchorage for the plant, and to collect and convey food ma- terials. The first function is considered in Chapter VII; we may now give attention in more detail to the second.
The feeding surface of the roots is near their ends. As the roots become old and hard, they serve only as channels through which food passes and as holdfasts or supports for the plant. The root- hold of a plant is very strong. Slowly pull upwards on some plant, and note how firmly it is anchored in the soil.
Roots have power to choose their food; that is, they do not absorb all substances with which they come in contact. They do not take up great quantities of useless or harmful materials, even though these materials may be abundant in the soil ; but they may take up a greater quantity of some of the plant-foods than the plant can use to advantage. Plants respond very quickly to liberal feeding, — that is, to the application of plant-food to the soil (Fig 40). The poorer the soil, the more marked are the results, as a rule, of the application
38
Fig. 40.-— Wheat growing under diffkkent soil Treatments. Soil defi- cient in nitrogen; com- mercial nitrogen applied to pot 3 (on right).
THE ROOT— FUNCTION AND STRUCTURE 39
of fertilizers. Certain substances, as common salt, will kill the roots.
Roots absorb Substances only in Solution. — Substances cannot be taken in solid particles. These materials are in solution in the soil water, and the roots themselves also have the power to dissolve the soil materials to some extent by means of substances that they excrete. The materials that come into the plant through the roots are water and mostly the min- eral substances^ as compounds of po- tassium, iron, phosphorus; calcium, magnesium, sulphur, and chlorine. These mineral substances compose the ash when the plant is burned. The carbon is derived from the air through the green parts. Oxygen is derived from the air and the soil water.
Nitrogen enters through the Roots.
— All plants must have nitrogen;
yet, although about four-fifths of F1G.41. — Nodules on roots ., . . .^ , ^ ^ OF Red /Clover.
the air is nitrogen, plants are not
able, so far as we know, to take it in through their leaves. It enters through the roots in combination with other ele- ments, chiefly in the form of nitrates (certain combinations with oxygen and a mineral base). The great family of leguminous plants, however (as peas, beans, cowpea, clover, alfalfa, vetch), use the nitrogen contained in the air in the soil. They are able to utilize it through the agency of nodules on their roots (Figs. 41, 42). These nodules contain bacteria, which appropriate the free or uncom- bined nitrogen and pass it on to the plant. The nitrogen
40
BEGIJVNEKS' BOTANY
Fig. 42.— Nodules on Vetch.
becomes incorporated in the plant tissue, so that these crops are high in their nitrogen content. Inasmuch as
nitrogen in any form is expensive to purchase in fertiUzers, the use of legu- minous crops to plough un- der is a very important ag- ricultural practice in pre- paring the land for other crops. In order that legum- inous crops ma}' acquire at- mospheric nitrogen more freely and thereby thrive better, ihe land is sometimes soivn or inoculated icith the nodule-forming hacteria.
Roots require moisture in order to serve the plant. The soil water that is valu- able to the plant is not the free water, but the t/iin film of moisture which adheres to each little particle of soil. The finer the soil, the greater the number of particles, and therefore the greater is the quantity of film moisture that it can hold. This moisture surround- ing the grains may not be perceptible, yet the plant can use it. Root absorption may continue in a soil which seems to be dust dry. Soils that are very hard and
Fig. 43. — Two Kinds of Soil that have BEEN Wet and then Dried. The loamy soil above remains loose and capa- ble of growing plants; the clay soil below has baked and cracked.
THE ROOT— FUNCTION AND STRUCTURE
41
"baked" (Fig. 43) contain very little moisture or air, — not so much as similar soils that are granular or mellow.
Proper Temperature for Root Action. — The root must be warm in order to perform its functions. Should the soil of fields or greenhouses be much colder than the air, the plant suffers. When in a warm atmosphere, or in a dry- atmosphere, plants need to absorb much water from the soil, and the roots must be warm if the root-hairs are to supply the water as rapidly as it is needed. If the roots are chilled^ the plant may wilt or die.
Roots need Air. — Corn on land that has been flooded by heavy rains loses its green colour and turns yellow. Besides diluting plant-food^ the water drives the air from the soily and this suffocation of the roots is very soon ap- parent in the general ill health of the plant. Stirring or tilling the soil aerates it. Water plants and bog plants have adapted them- selves to their particular conditions. They get their air either by special surface roots, or from the water through stems and leaves.
Rootlets. — Roots divide into the thinnest and finest fibrils : there are roots and there are rootlets. The smallest rootlets are so slender and delicate that they break off even when the plant is very carefully lifted from the soil.
The rootlets^ or fi7te divisions^ ai^e clothed with the root- hairs (Figs. 44, 45, 46). These root-hairs attach to the soil particles y and a great amount of soil is thus brought into actual contact with the plant. These are very deli- cate prolonged surface cells of the roots. They are borne for a short distance just back of the tip of the root.
Rootlet and root-hair differ. The rootlet is a compact
Fig. 44. — Root- hairs OF THE Radish.
42
1,
y
BEGINNERS' BOTANY
Fig. 45, — Cross-section of Root, enlarged, showing root-hairs.
cellular structure. The root-hair is a delicate tub7ilaf cell (Fig. 45), within which is contained livifig- matter
(protoplasm) ; and the protoplasmic lining niembrane of the
wall governs the entrance of water and substances in solu- tion. Being long and tube- like, these root-hairs are especially adapted for tak- ing in the largest quantity of solutions; and they are the principal means by which plant-food is absorbed from the soil, although the sur- faces of the rootlets them- selves do their part. Water plants do not produce an
abundant system of root-hairs, and such plants depend
largely on their rootlets.
The root-hairs are very small, often invisible. They,
with the young roots, are usually broken off when the
plant is pulled up. They are
best seen when seeds are germin- ated between layers of dark
blotting paper or flannel. On
the young roots they will be
seen as a mould-like or gossamer- like covering. Root-hairs soon
die : they do not grow into roots.
New ones form as the root grows. Osmosis. — The water with its
nourishment goes through the
thin walls of the root-hairs and rootlets by the process
of osmosis. If there are two liquids of different density
Fig. 46. — RooT-HAiR, much en- larged, in contact with the soil particles (j) . Air-spaces at a \ water-films on the particles, as at w.
THE ROOT— FUNCTION AND STRUCTURE 43
on the inside and outside of an organic (either vegetable or animal) membrane, the liquids tend to mix through the membrane. The law of osmosis is that the most rapid flow is toward the denser solution. The protoplasmic lin- ing of the cell wall is such a membrane. The soil water being a weaker solution than the sap in the roots, the flow is into the root. A strong fertilizer sometimes causes a plant to wither, or "burns it." Explain.
Structure of Roots. — The root that grows from the lower end of the caulicle is the first or primary root. Secondary roots branch from the primary root. Branches of second- ary roots are sometimes called tertiary roots. Do the sec- ondary roots grow from the cortex, or from the central cylinder of the primary root.^ Trim or peel the cortex from a root and its branches and determine whether the branches still hold to the central cylinder of the main root.
Internal Structure of Roots. — A section of a root shows that it consists of a central cylinder (see Fig. 45) sur- rounded by a layer. This layer is called the cortex. The outer layer of cells in the cortex is called the epidermis, and some of the cells of the epidermis are prolonged and form the delicate root-hairs. The cortex resembles the bark of the stem in its nature. The central cylinder contains many tube-Hke canals, or " vessels " that convey water and food (Fig. 45). Cut a sweet potato across (also a radish and a turnip) and distinguish the central cylin- der, cortex, and epidermis. Notice the hard cap on the tip of roots. Roots differ from stems in having no real pith.
Microscopic Structure of Roots. — Near the end of any young root or shoot the cells are found to differ from one an- other more or less, according to the distance from the point. This diffei'entiation takes place in the region just back of the growing point. To study growing points, use
44
BEGINNERS* BOTANY
the hypocotyl of Indian corn which has grown about one- half inch. Make a longitudinal section. Note these points (Fig. 47): {a) the tapering root-cap beyond the growing point ; {b) the blunt end of the root proper and the rec- tangular shape of the cells found there; {c) the group of cells in the middle of the first layers beneath the root- cap, — this group is the growing point; {d) study the sUght differ- ences in the tissues a short dis- tance back of the growing point. There are four regions : the central cylinder, made up of several rows of cells in the centre (//); the en- dodermis, (e) composed of a single layer on each side which separates the central cylinder from the bark ; the cortex, or inner bark, {e) of sev- eral layers outside the endodermis ; and the epidermis, or outer layer of bark on the outer edges {d). Make a drawing of the section. If a series of the cross-sections of the hypocotyl should be made and stud- ied by the pupil beginning near the growing point and going up- ward, it would be found that these four tissues become more distinctly marked, for at the tip the tissues have not yet assumed their characteristic form. The central cylinder contains the ducts and vessels which convey the sap.
The Root-cap. — Note the form of the root-cap shown in the microscopic section drawn in Fig. 47. Growing cells, and especially those which are forming tissue by sub- dividing, are very deHcate and are easily injured. The
Fig. 47. — Growing Point OF Root of Indian Corn.
d, d, cells which will form the epidermis; /, /, cells that will form bark; <», ^, endoder- mis; //, cells which will form the axis cylinder; /, initial group of cells, or growing point proper; c, root-cap.
THE ROOT-- FUNCTION AND STRUCTURE
45
cells forming the root-cap are older and tougher and are suited for pushing aside the soil that the root may pene- trate it.
Region of most Rapid Growth. — The roots of a seedling bean may be marked at equal distances by waterproof ink or by bits of black thread tied moderately tight. The seedling is then replanted and left undisturbed for two days. When it is dug up, the region of most rapid growth in the
Fig. 48. —The Mark- ing OF THE Stem AND Root.
Fig. 49.— The Result
root can be deter- mined. Give a reason why a root cannot elongate thfoiighoiit its length, — whether there is anything to pre- vent a young root from doing so.
In Fig. 48 is shown a germinating scarlet runner bean with a short root upon which are marks made with waterproof ink; and the same root (Fig. 49) is shown after it has grown longer. Which part of it did not lengthen at all } Which part lengthened slightly .? Where is the region of most rapid growth.!* Geotropism. — Roots turn to- ward the earth, even if the seed is planted with the micropyle up. This phenomenon is called posi- tive geotropism. Stems grow away from the earth. This is negative geotropism.
46
BEGINNERS' BOTANY
Suggestions (Chaps. VII and VIII). — 25. Tests for food. Ex- amine a number of roots, including several fleshy roots, for the presence of food material, making the tests used on seeds. 26. Study of root-hairs. Carefully germinate radish, turnip, cabbage, or other seed, so that no delicate parts of the root will be injured. For this purpose, place a few seeds in packing-moss or in the folds of thick cloth or of blotting paper, being careful to keep them moist and warm. In a few days the seed has germinated, and the root has grown an inch or two long. Notice that, except at a dis- tance of about a quarter of an inch behind the tip, the root is covered with minute hairs (Fig. 44). They are actually hairs; that is, root-hairs. Touch them and they collapse, they are so delicate. Dip one of the plants in water, and when removed the hairs are not to be seen. The water mats them together along the root and they are no longer evident. Root-hairs are usually destroyed when a plant is pulled out of the soil, be it done ever so carefully. They cling to the minute particles of soil (Fig. 46). The hairs show best against a dark background. 27. On some of the blotting papers, sprinkle sand ; observe how the root-hairs cling to the grains. Observe how they are flat- tened when they come in contact with grains of sand. 28. Root
hold of plant. The pupil should also study the root hold. Let him carefully pull up a plant. If a plant grow alongside a fence or other rigid object, he may test the root hold by se- curing a string to the plant, letting the string hang over the fence, and then add- ing weights to the string. Will a stake of similar size to the plant and extending no deeper in the ground have such firm hold on the soil? What holds the ball of earth in Fig. 50? 29. Roots exert pressure. Place a strong bulb of hyacinth or daffodil on firm-packed earth in a pot ; cover the bulb nearly to the top with loose earth j place in a cool cellar ; after some days
Fig, 50.— Th^ Grasp of a Plant on the Parti- cles OF Earth. A grass plant pulled in a garden.
THE ROOT-^ FUNCTION AND STRUCTURE
47
Fig. 51.— Plant grow- ing IN In- verted Pot.
or weeks, note that the bulb has been raised out of the earth by the forming roots. All roots exert pressure on the soil as they grow. Explain. 30. Response of roots and stems to the force of gravity^ or geotropism. Plant a fast-growing seedling in a pot so that the plumule extends through the drain hole and suspend the pot with mouth up {i.e. in the usual position). Or use a pot in which a plant is already growing, cover with cloth or wire gauze to prevent the soil from falling, and suspend the pot in an inverted position (Fig. 51). Notice the behaviour of the stem, and after a few days remove the soil and observe the position of the root. 31. If a pot is laid on one side, and changed every two days and laid on its opposite side, the effect on the root and stem will be interesting. 32. If a fleshy root is planted wrong end up, what is the result ? Try it with pieces of horse-radish root. 33. By planting radishes on a slowly revolving wheel the effectofgravity may be neutralized. 34. Region of root most sensitive to gravity. Lay on its side a pot containing a growing plant. After it has grown a few days, wash away the earth surrounding the roots. Which turned downward most decidedly, the tip of root or the upper part? 25. Soil texture. Carefully turn up soil in a rich garden or field so that you have unbroken lumps as large as a hen's tgg. Then break these lumps apart carefully ^^^^^^^^^__^^____^^^_^_^______^_^^^^ with the fingers and
/^^IS^^^^Sc^^lt^^^^^^l^'^r^^TT^ determine whether
there are any traces or remains of roots (Fig. 52). Are there any pores, holes, or channels made by roots ? Are the roots in them still living? 36. Compare an- other lump from a clay bank or pile where no plants have been growing. Is there any differ- ence in texture ? 37. Grind up this clay lump very fine, put it in a saucer, cover with water, and set in the sun. After a time it will have the appearance shown in the lower saucer in Fig. 43. Compare this with mellow garden soil. In which will plants grow best, even if the plant- food were the same in both ? Why ? 38. To test the effect of moisture on the plant, let a plant in a pot or box dry
Fig. 52. — Holes in Soil made by Roots, now decayed. Somewhat magnified.
48 BEGINNERS* BOTANY
out till it wilts ; then add water and note the rapidity with which it recovers. Vary the experiment in quantity of water appUed. Does the plant call for water sooner when it stands in a sunny win- dow than when in a cool shady place? Prove it. 39. Immerse a potted plant above the rim of the pot in a pail of water and let it remain there. What is the consequence ? Why ? 40. To test the effect of temperature on roots. Put one pot in a dish of ice water, and another in a dish of warm water, and keep them in a warm room. In a short time notice how stiff and vigorous is the one whose roots are warm, whereas the other may show signs of wilting. 41. The process of osmosis. Chip away the shell from the large end of an egg so as to expose the uninjured membrane beneath for an area about as large as a ten-cent piece. With sealingr- wax, chewing-gum, or paste, stick a quill about three inches long to the smaller end of the ^^g. After the tube is in place, run a hat pin into it so as to pierce both shell and membrane ; or use a short glass tube, first scraping the shell thin with a knife and then boring through it with the tube. Now set the egg upon the mouth of a pickle jar nearly full of water, so that the large end with the exposed membrane is beneath the water. After several hours, observe the tube on top of the egg to see whether the water has forced its way into the egg and increased its volume so that part of its contents are forced up into the tube. If no tube is at hand, see whether the contents are forced through the hole which has been made in the small end of the egg. Explain how the law of osmosis is verified by your result. If the eggshell contained only the membrane, would water rise into it? If there were no water in the bottle, would the egg-white pass down into the bot- tle? 42. The region of most rapid growth. The pupil should make marks with waterproof ink (as Higgins' ink or indelible marking ink) on any soft growing roots. Place seeds of bean, radish, or cabbage between layers of blotting paper or thick cloth. Keep them damp and warm. When stem and root have grown an inch and a half long each, with waterproof ink mark spaces exactly one-quarter inch apart (Figs. 48, 49). Keep the plantlets moist for a day or two, and it will be found that on the stem some or all of the marks are more than one-quarter inch apart; on the root the marks have not separated. The root has grown beyond the last mark.
CHAPTER IX THE STEM — KINDS AND FORMS; PRUNING
The Stem System. — The stem of a plant is the part that bears the btids^ leaves^ flowers^ and fruits. Its office is io hold these parts up to the light and the air; and through its tissues the various food-materials and the life- giving fluids are distributed to the growing and working parts.
The entire mass or fabric of stems of any plant is called its stem system. It comprises the trunk, branches, and twigs, but not the stalks of leaves and flowers that die and fall away. The stem system may be herbaceous or woody, annual, biennial, or perennial ; and it may assume many sizes and shapes.
Stems are of Many Forms. — The general way in which a plant grows is called its habit. The habit is the appear- ance or general form. Its habit may be open or loose, dense, straight, crooked, compact, straggling, climbing, erect, weak, strong, and the like. The roots and the leaves are the important functional or ivoi'king parts ; the stem merely connects them, and its form is exceedingly variable.
Kinds of Stems. — The stem may be so short as io be scarcely distinguishable. In such cases the crown of the plant — that part just at the surface of the ground — bears the leaves and the flowers ; hut this crown is really a very short stem. The dandelion, Fig. 33, is an example. Such plants are often said to be stemless, however, in order to distinguish them from plants that have long or conspic- E 49
so
BEGINNERS' BOTANY
uous Stems. These so^alled stemless plants die to the ground every year.
Stems are erect when they grow straight up (Figs. 53, 54). They are trailing when they run along on the ground,
Fig. 53. — Strict Simple Stem of Mullein.
Fig. 54. — Strict Upright Stem OF Narrow-leaved Dock.
as melon, wild morning-glory (Fig. 55). They are creep- ing when they run on the ground and take root at places,
Fig. 55.— Trailing Stem of Wild Morning Glory {Convolvulus arvensis).
as the strawberry. They are decumbent when they lop over to the ground. They are ascending when they lie mostly or in part on the ground but stand more or less upright at their ends; example, a tomato. They are
THE STEMS— KINDS AND FORMS; PRUNING
51
climbiiig when they cling to other objects for support (Figs. 36, 56).
Trees in which the main trunk or the ** leader'* continues to grow from its tip are said to be excurrent in growth. The branches are borne along the sides of the trunk, as in common pines (Fig. 57) and spruces. Excurrent means running out or running up.
Trees in which the main trunk does not continue are said to be deliques- cent. The brandies arise from 07ie common point or from each other. The stem is lost in the branches. The apple tree, plum (Fig. 58), maple, elm, oak, China tree, are familiar examples. Deliquescent means dissolving or melting away.
Each kind of plant has its own peculiar
habit or direction of growth. Spruces al-
'ways grow to a single stem or trunk, pear
Fig. 56. — a
Climbing Plant
(a twiner).
Fig. 57. — Excurrent Trunk. A pine.
Fig. 58. — Deliquescent Trunk OF Plum Tree.
52 BEGINNERS' BOTANY
trees are always deliquescent, morning-glories are always trailing or climbing, strawberries are always creeping. We do not know why each plant has its own habit, but the habit is in some way associated with the plant's gene- alogy or with the way in which it has been obliged to live.
The stem may be simple or branched. A simple stem usually grows from the terminal bud, and side branches either do not start, or, if they start, they soon perish. Mulleins (Fig. 53) are usually simple. So are palms.
Branched stems may be of very different habit and shape. Some stem systems are narrow and erect ; these are said to be strict (Fig. 54). Others are diffuse, open, branchy, twiggy.
Nodes and Internodes. — The parts of the stem at which buds grow are called nodes or joints and the spaces be- tween the buds are internodes. The stem at nodes is usually enlarged, and the pith is usually interrupted. The distance between the nodes is influenced by the vigour of the plant : how }
Fig. 59.— Rhizome or Rootstock.
Stems vs. Roots. — Roots sometimes grow above ground (Chap. VII); so, also, stems sometimes gtoiv underground, and they are then known as subterranean stems, rhizomes, or rootstocks (Fig. 59).
Stems normally bear leaves and buds, and thereby are they distinguished from roots; usually, also, they contain a pith. The leaves, however, may be reduced to mere scales, and the buds beneath them may be scarcely visible.
THE STEMS— KINDS AND FORMS; PRUNING 53
Thus the " eyes " on a white potato are cavities with a bud or buds at the bottom (Fig. 60). Sweet potatoes have no evident " eyes " when first dug, (but they may develop adventitious buds before the next grow- ing-season). The white potato is a stem : the sweet potato is probably a root.
How Stems elongate. — Roots elongate by growing near the tip. Stems elon- gate by growijtg more or less throusrh- ^^^"' ^- ~ Sprouts
^ -^ <^ ^ o ARISING FROM THE
out the young or soft part or " between buds, or eyes, of a joints " (Figs. 48, 49). But any part P°'^'° '"^^'■• of the stem soon reaches a limit beyond which it cannot grow, or becomes "fixed"; and the new parts beyond elongate until they, too, become rigid. When a part of the stem once becomes fixed or hard, it never increases in length : that is, tJie trunk or woody parts never grow longer or higher ; branches do not become farther apart or higher from the ground.
Stems are modified in form by the particular or incidental conditions under which they grow. The struggle for light is the chief factor in determining the shape and the direc- tion of any limb (Chap. II). This is well illustrated in any tree or bush that grows against a building or on the mar- gin of a forest (Fig. 4). In a very dense thicket the innermost trees shoot up over the others or they perish. Examine any stem and endeavour to determine why it took its particular form.
The stem is cylindrical, the outer part being bark and the inner part being wood or woody tissue. In the dicoty- ledonous plants, the bark is usually easily separated from the remainder of the cyHnder at some time of the year ; in monocotyledonous plants the bark is not free. Growth in thickness takes place inside the covering and not on the very
54
BE G INNER S' BOTANY
outside of the plant cylinder. It is evident, then, that the covering of bark must expandin order to allow of the expan- sion of the woody cylinder within it. The tis- sues, therefore, must be under constant pressure or tension. It has been determined that the pressure within a growing trunk is often as much as fifty pounds to the square inch. The lower part of the limb in Fig. 6i shows that the outer layers of bark (which are long since dead, and serve only as protective tissue) have reached the Hmit of their expanding capacity and have begun to split. The pupil will now be interested in the bark on the body of an old elm tree (Fig. 62); and he should be able to suggest one reason why stems remain cylindri- cal, and why the old bark becomes marked with furrows, scales, and plates.
Most woody plants increase in diameter by the addition of an annual layer or *'ring'' on the Branch. outside of the woody cylinder, underneath the bark. The monocotyledo- nous plants comprise very few trees and shrubs in temperate climates (the palms, yuccas, and other tree-like plants are of this class), and they do not increase greatly in diameter and they rarely branch to any extent.
Bark-bound Trees. — If, for any rea- son, the bark should become so dense and strong that the trunk cannot ex- pand, the tree is said to be ' 'bark-bound." Such condition is not rare in orchard trees tliat have been neglected. When good tillage is given tc such trees, they
Fig. 62. — Piece of Bark from an Old Elm Trunk.
THE STEMS— KINDS AND FORMS; TRUNIN G
55
may not be able to overcome the rigidity of the old bark, and, therefore, do not respond to the treatment. Sometimes the parts with thinner bark may outgrow in diameter the trunk or the old branches below them. The remedy is to release the tension. This may be done either by soften- ing the bark (by washes of soap or lye), or by separating it. The latter is done by slitting the bark-bound part (in spring), thrusting the point of a knife through the bark to the wood, and then drawing the blade down the entire length of the bark- bound part. The slit is scarcely discernible at first, but it opens with the growth of the tree, filHng up with new tissue beneath. Let the pupil consider the ridges which he now and then finds on trees, and determine whether they have any sig- nificance— whether the tree has ever been released, or in- jured by natural agencies.
The Tissue covers the Wounds and "heals" them. — This is seen in Fig. 63, in which a ring of tissue rolls out over the wound. This ring of healing tissue forms most rapidly and uniformly when the wound is smooth and regu- lar. Observe the healing on broken and splintered limbs; also the difference in rapidity of healing between wounds on strong and weak limbs. There is a diflPerence in the rapidity of the healing process in different kinds of trees. Compare the apple tree and the peach. This tissue may in
Fig. 63. — Proper Cuthng of a Branch. The wound will soon be "healed."
56
BE GINNKRS ' BOTANY
Fig. 64. — Erroneous Pruning.
turn become bark-bound, and the healing may stop. On large wounds it progresses more rapidly the first few years
than it does later. This roll or ring of tissue is called a callus.
The callus grows from the liv- ing tissue of the stem just about the wound. It cannot cover long dead stubs or very rough broken branches (Fig. 64). Therefore, in pruning the brandies should be cut close to the trunk and made even and smooth ; all long stubs must be avoided. The seat of the wound should be close to the living part of the trunk, for the stub of the limb that is severed has no further power in itself of making heaUng tissue. The end of the remaining stub is merely covered over by the callus, and usually remains a dead piece of wood sealed in- side the trunk (Fig. 65). If wounds do not heal over speed- ily, germs and fungi obtain foothold in the dying wood and rot sets in. Hollow trees are those in which the decay- fungi have progressed into the inner wood of the trunk ; they have been infected {¥\g. 66).
Large wounds should be protected with a covering of paint, melted wax, or other adhesive and lasting material,
Fig. 65. — Knot in a Hemlock Log.
THE STEMS— KINDS AND FORMS; PRUNING
57
Fig. 66.— a Knot Hole, and the beginning of a hollow trunk.
to keep out the germs and fungi. A covering of sheet iron or tin may- keep out the rain, but it will not ex- clude the germs of decay ; in fact, it may provide tlie very moist con- ditions that such germs need for their growth. Deep holes in trees should be. treated by having all the decayed parts removed down to the clean wood, the surfaces painted or otherwise sterilized, and the hole filled with wax or cement. Stems and roots are living, and
they should not be wounded or
mutilated unnecessarily. Horses
should never be hitched to trees.
Supervision should be exercised
over persons who run telephone,
telegraph, and electric light wires,
to see that they do not mutilate
trees. Electric light wires and trol- ley wires, when carelessly strung
or improperly insulated, may kill
trees (Fig. 6'j).
Suggestions. — Forms of stems.
43. Are the trunks of trees ever per- fectly cylindrical? If not, what may cause the irregularities ? Do trunks often grow more on one side than the other?
44. SHt a rapidly growing limb, in spring,
with a knife blade, and watch the result during the season. 45. Examine the w«odpile, and observe the variations in thickness of the annual rings, and especi- ally of the same ring at different places in the circumference. Cross-sections of
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Fig. 67. — Elm Tree killed BY A Direct Current FROM AN Electric Railroad System.
58
BEG/NNEKS' BOTANY
horizontal branches are interesting in this connection. 46. Note the enlargement at the base of a branch, and determine whether this enlargement or bulge is larger on long, horizontal limbs than on upright ones. Why does this bulge develop? Does it serve as a brace to the limb, and is it developed as the result of constant strain? 47. Strength of stems. The pupil should observe the fact that a stem has wonderful strength. Compare the propor- tionate height, diameter, and weight of a grass stem with those of the slenderest tower or steeple. Which has the greater strength? Which the greater height? Which will withstand the most wind? Note that the grass stem will regain its position even if its top is bent to the ground. Note how plants are weighted down after a heavy rain and how they recover themselves. 48. Split a corn- stalk and observe how the joints are tied together and braced with fibres. Are there similar fibres in steins of pigweed, cotton, sun- flower, hollyhock?
Fig. 68. — Potato. What are roots, and what stems ? Has tlie plant more than one kind of stem ? more than two kinds ? Explain.
CHAPTER X
THE STEM — ITS GENERAL STRUCTURE
There are two main types of stem structure in flowering plants, the differences being based on the arrangement ot bundles or strands of tissue. These types are endogenous and exogenous (page 20). It will require patient laboratory work to understand what these types and structures are.
Endogenous, or Monocotyledonous Stems. — Examples of endogenous stems are all the grasses, cane-brake, sugar- cane, smilax or green-brier, palms, banana, canna, bam- boo, lilies, yucca, aspara- gus, all the cereal grains. For our study, a cornstalk may be used as a type.
A piece of cornstalk^ either green or dead, should be in the hand of each pupil while studying this lesson. Fig. 69 will also be of use. Is there a swelling at the nodes.!* Which part of the internode comes nearest to being perfectly round } There is a grooved channel running along one side of the internode : how is it placed with reference to the leaf ? with reference to the groove in the internode below it ? What do you find in each groove at its lower end? (In a dried stalk only traces of this are usually seen.) Does any bud on a cornstalk besides the one at
59
Fig. 69. — Cross-section of Corn- stalk, showing the scattered fibro- vascular bundles. Slightly enlarged.
6o
BEGINNERS' BOTANY
the top ever develop ? Where do suckers come from ? Where does the ear grow ?
Cut a cross-section of the stalk between the nodes (Fig. 69). Does it have a distinct bark ? The interior consists of soft **pith" and tough woody parts. The wood is found in strands or fibres. Which is more abundant? Do the fibres have any definite arrangement ? Which strands are largest.? Smallest."* The firm smooth rind {which cannot properly be called a bark) consists of small wood strands packed closely together. Grass stems are hollow cylinders ; and the cornstalk, because of the lightness of its contents, is also practically a cylinder. Stems of this kind are ad- mirably adapted for providing a strong support to leaves and fruit. This is in accordance with the well-known law that a hollow cylinder is much stronger than a solid cylinder of the same weight of material. Cut a thin slice of the inner soft part and hold it up to the light. Can you make out a number of tiny compartments or cells.? These cells consist of a tissue called paren- chyma^ the tissue from which when young all the other tissues arise and differentiate. The numerous walls of these cells may serve to brace the outer wall of the cylinder ; but their chief function in the young stalk is to give origin to other cells. When alive they are filled with cell sap and protoplasm.
Trace the woody strands through the nodes. Do they ascend vertically } Do they curve 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
Fig. 70. — Dia- gram TO SHOW THE Course of
FiBRO- VASCU- LAR Bundles IN Monocoty- ledons.
THE STEM— ITS GENERAL STRUCTURE
6l
Fig. 71.— Diagram of Wood Strands or
FiBRO-VASCULAR
Bundles in a Root, showing the wood (jr) and bast (/) separated.
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
fibro-vascular bundle) consists of two
parts — the bast and the wood proper.
The wood is on the side of the strand
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 two kinds of strands.
In monocotyledons, as already said, the strands (or bundles) are usually scattered in the
stem with no definite arrangement (Figs. 72, 73). In
dicotyledons the strands, or bundles, are arranged in a
Fig. 72. — Part of Cross-section of Root- stock OF Asparagus, showing a few fibro- vascular bundles. An endogenous stem.
62
BRCrNNERS* BOTANY
Scattered Bundles or Strands, in monocotyledons at a, and the bun- dles in a circle in dicotyledons at b.
Fio. 74. —Dicotyledonous Stem of One Year at Left
WITH Five Bundles, and a two-year stem at right. <7, the pith; c, the wood part ; ^, the bast part; a, one year's growth.
ring. As the dicotyledonous seed germi- Fio. 73. — The nates, five bundles are usually formed in
its hypocotyl (Fig. 74); soon five more are
interposed
between
them, and
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 or bast. A new ring of wood or bast is formed on stems of di- cotyledons each year, and
the age of a cut stem is
„ ., J . . J Fig. 75. — Fibro-vascular Bundle of
easily determmed. i.,^,^^, corn, much magnified.
When cross-sections of ^, annular vessel ; ^', annular or spiral vessel ; ♦^^^^^^4. 1 J IT ^^» thick-walled vessels; W, tracheids or
mOnOCOtyledonOUS and dl- ^^ody tissue ; F, sheath of fibrous tissue sur-
rounding the bundle ; FT, fundamental tissue or pith ; S, sieve tissue ; P, sieve plate ; C, companion cell ; /, intercellular space, formed by tearing down of adjacent cells ; VV , wood parenchyma.
cotyledonous bundles are examined under the mi- croscope, it is readily seen
THE STEM— ITS GENERAL STRUCTURE
63
why dicotyledonous bundles form rings of wood and mono- cotyledonous cannot (Figs. 75 and 'j^). The dicotyledon- ous bundle (Fig. ^6) 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 :
r, cambium ; </, ducts ; i, 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: h, wood- cells; ^.vessels; <:, cambium; /.fundamental tissue or parenchyma; ^, bast; ^/, 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 sterns 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, s years old. The outermost layer is bark.
late season, and the spring wood is less dense and of a lighter colour 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 Hve a century. It is 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. Therie are also
wood fibres which /, pith; /, parenchyma
are thick-walled
|
AIX |
||
|
^ |
||
|
s |
^ |
|
|
^ |
V^ |
|
|
^ |
S |
|
|
H |
SO
Fig. 78. — Arrangement of Tissues in Two - yea r- OLD Stem of Moonseed.
The fibro- vascular bundles, or wood strands, are very prominent, with Fig. 79. — Markings and rigid (h, Fig. thin medullary rays between.
IN Cell Walls rr/^N i . . xi i
OF Wood Fibre '^h ^nd servc to support the sap-canals
j/, spiral ; an, annular sc, scalariform.
or wood vessels (or tracheids) that are 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 pecuHar 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 pits (,^, Fig. 76). These thin spots
(Fig. 80) allow the sap to pass to other p^^ g^
cells or to neighbouring vessels. The cambium, as we have seen, consists '^t^ttThtlt
of cells whose function is growth. These pit borders at o, *,
Pits in THE Cell Wall.
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 several kinds of tissue, all sepa- rating from the wood beneath by means of cambium. The new bast contains (i) the sieve-tubes (Fig. 8i) which transport the
sap containing organic substances, as sugar
and proteids, from the leaves to the parts
needing it {s, Fig. j6\ 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 bast
fibres (Fig. 82) in the bast that serve
for support. (3) Tlioro is also some
parenchyma in the new l;ast; it is Fig. 82.— thick-
, , , . ei WALLED BaST
now m part a storage tissue. borne- cells.
Fig. 81. — Sieve-tubes, j, j;
/ shows a top view of a sieve-plate, with a companion cell, c, at the side; o shows sieve-plates in the side of the cell. In s, s the proto- plasm is shrunken from the walls by reagents.
THE STEM— ITS GENERAL STRUCTURE 6/
times the walls of parenchyma cells in the cortex thicken at the corners and form brace 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 FIG. 83. - COLL EN- secretions (milk, CHYMA IN Wild rosin, etc.) and
TEWELWEED or 11 1 r
TOUCH-ME-NOT (IM- ^^^ Callcd lutCX
PATIENS). tubes. ^'''- ^'*- -^^'"^ ^'^''^'•
The outer bark of old shoots consists of corky cells that protect from mechanical injury, and that contain a fatty sub- stance (suberin) impermeable to water and of service to keep m moisture. There is sometimes a cork cambium (or phellogen) in the bark that serves to extend the bark and 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: (i) the root zvater, 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, ifi the ivood vessels, — that is, in the young or "sapwood " (p. 96); (2) Xho, elaborated or oi'gani:;ed materials Y^^iSsmghdick 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, in the sieve-tubes of the inner bast, — that is, in the ** inner bark." Removing the bark from a trunk in
6S
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 or trunk, and sometimes the 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 (mul- berry^ cedar^ post oak^ bois d'arCy mesqtiite).
Hardness and strength are qualities of great value in building. Live oak is used in ships. Red oaky rock maple^
Fig. 85.— The Wrong Way to BRACE A Tree. (See Fig. iiS;.
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 bois d'arc (osage orange) are used for hubs of wheels; bois d'arc makes a remarkably durable pavement for streets. Ebony is a tropical wood used for flutes, black piano keys, and fancy articles. Ash is straight and elastic ; it is used for handles for Hght implements. Hickory 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 lumber, 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 is oftejz 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, y^laiie 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. Willow is useful for bas- kets and light furniture. Basswood or linden is used for light ceiling and sometimes for cheap floors. Whitewood
70
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. Mahogany 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. Z6 shows one
mode of quartering. The log is quartered on the lines a, a, byb \ then succeeding boards are cut from each" quarter at i, 2, 3, etc. The nearer the heart the better the "grain" : why? Ordinary boards are sawn tangentially, as c^ c. Curly pine, curly walnut, and bird's-eye maple are 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 oilier woods in luakiiijj^ 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. Maple is much used for furniture. Birch may be coloured so as very closely to represent mahogany, and it is useful for desks.
Special Products of Trees. — Cork from llic hark of tJic cork oak in Spain, latex from the rubber, and sap from the
Fig. 86. — The Making of Ordinary Boards, AND One V^ay of Making " Quartered " Boards.
THE STEM— ITS GENERAL STRUCTURE *J\
sugar-maple trees, turpentine from pine, tannin from oak bark, Peruvian bark from cinchona, are all useful products.
Suggestions. — Parts of a root and stem through which liquids rise. 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 {U) 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?
Note 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.
Fig. 87. — The Many-stemmed Thickets of Mangrove of Southern- most Seacoasts, many of the trunks being formed of aerial roots.
CHAPTER XI
LEAVES — FORM AND POSITION
Leaves may be studied from four points of view, — with reference to (1) their kinds and shapes; {2) their position, or arrangemefit on the plant; (3) their anatomy , or structure ;
Fig. 88. — a Simple Netted-veined Leaf.
(4) their functiouy or the work they perform. This chapter is concerned with the first ,4t two categories.
Fig. 90. — Compound or Branched Leaf OF Brake (a common fern).
Fig. 89. — a Simple Par- allel-veined Leaf.
Kinds. — Leaves are simple or un- branchcd (Figs. ^Z, 89), and compound or branched (Fig. 90),
73
H
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 when the veins arise from the side of a continuous midrib (Fig. 91); palmate or digitate (hand-like) when the veins arise from the apex of the petiole (Figs. Z^, 92). If leaves were divided between the main veins, the former would be pinnately arid 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. 91. — Com- plete Leaves of Willow.
Fig. 92. — Digitate-veined Pel- tate Leaf of Nasturtium.
Fig. 93. — Pinnately Compound 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
n
Sometimes the leaflets themselves are compound, and the whole leaf is then said to be bi-compound or twice-com-
FlG. 94, — DlGI-
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 express any 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 pio. 96. - Lobed leaf of than the middle ; Sugar Maple.
76
BEGINNERS* BOTANY
Fig. 97. — Digitately Parted Leaves OF Begonia.
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- lets. The leaf may be pinnately or digitately A pinnately parted or
lobed, parted, cleft, or divided.
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 appendages at the base of the petiole. A leaf that has all three of these parts is said to be complete (Figs. 91, 106). The stipules are often green and leaflike and per- form the function fig. 98 of foliage as in the 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), i,e. sitting. Find several examples.
Oblong
ovate Sessile Leaves of Tea.
LEAVES'- FORM AND POSITION
77
Fig. 99.— Clasp- ing Leaf of a "Wild Aster.
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 opposite sessile leaves are joined by their bases, they are said to be connate (Fig. loi). 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- olules, and stipels.
The blade is usually attached to the petiole by its 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 usuafly digitate-veined.
How to Tell a Leaf.— It is often difficult to distin-
guishcompound leaves from ^^^ ,01. -Two Pairs of Connate leafy branches, and leaflets Leaves of Honeysuckle.
Fig. 100. — De- current Leaves of Mullein.
78
BEGINNERS' BOTANY
from leaves. As a rule leaves can be distinguished by the following tests : ( i ) Leaves are temporary strjictures^ sooner or later falling. (2) Usually buds are borne in their axils, (3) Leaves are usually borne at joints or nodes. (4) They arise on wood of the curre7it year's growth. (5) They have a more or less defiiiite 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. The shapes are likened to those of famihar ob- jects or of geometrical figures. Some of the commoner shapes are as follows (name original examples in each class): 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.
Fig. 102.— Linear- acuminate Leaf of Grass.
Fig. 103. — Short-oblong Leaves of Box.
LEAVES— FORM AND POSITION
79
Elliptic differs from the oblong in having the sides gradu- ally tapering to either end from the middle. The
^k 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
V tapering to either end. Some of the narrow-leaved willows are examples. Most of the willows and the peach have oblong-lanceolate leaves. Spatulate, a narrow leaf that is broadest
\ toward the apex. The top is usually rounded.
104. —
Elliptic Leaf
OF Purple
Beech.
Fig. 105. — Ovate Serrate Leaf of Hibiscus.
Fig. 106. — Leaf of Apple, showing blade, petiole, and small narrow stipules.
Ovate, shaped somewhat like the longitudinal section of an ^ Q^gg\ about twice as long as broad, tapering from near ^ the base to the apex. This is one of the commonest ^ leaf forms (Figs. 105, 106).
8o
BEGINNERS' BOTANY
Obovate, ovate inverted, — the wide part towards the apex.
Leaves of mullein and leaflets of horse-chestnut and S false indigo are obovate. This form is commonest
in leaflets of digitate leaves : why ? Reniform, kidney-shaped. This form is sometimes seen in ^^ 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 LoBED Leaves.
Fig. 108.— Truncate 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
8i
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 growths 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- 5is (Fig. 109), a vine ihat is used to cover brick and stone build- ings. Different degrees of compounding, even in the same leaf, may often be found in honey locust. Remarkable dif- ferences in forms are 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 grozvs. Floati7tg leaves are usually expanded and flaty and the petiole varies in length with the depth of the water. Submerged leaves are usually linear or thread- likCf 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
Fig. 109. — Different Forms of Leaves FROM one Plant of Ampelopsis.
82 BEGINNERS* BOTANY
branches or in the interior of the tree top. In dense foliage masses, the petioles of the lowermost or under- most leaves tend 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 distinct 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. TJiis position or directio7t is determined largely by exposure to sunlight. In temperate chmates 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. 1 10. O^te pair does not shade the pair beneath. The leaves are in four vertical ranks.
There are several kinds of alternate arrangement. In the elm shoot, in Fig. no, the third bud is vertically above the first. This 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 fraction \y which expresses the part of the circle that lies 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. 1 10, right) the thread makes two circuits and five buds are passed : two fifths represents the divergence between the buds. The leaves are 5-ranked.
Every plant has its 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
Fig, iio. — Phyij.otaxy of Box Elder, EiM. Apple.
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. 1 1 1). The arrange^nent of leaves on the stem is 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, it is subject to
modification. On shoots that receive the
Fig. III. — light only from one side or that grow in dif-
^Tthe^po^ ficult positions, the arrangement may not be
TATo Tuber, definite, Examine shoots that grow on the
w^ork It out under side of dense tree tops or in other par-
on a fresh *^ *
long tuber. tially lighted positions.
Suggestions. — 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 8$
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 ?
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 a compound 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.
CHAPTER XII
LEAVES — STRUCTURE OR ANATOMY
Besides 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 not 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- rophyll drops imbedded in the protoplasm. Below the pali- sade cells is the
Fig. 113. — Section of a Leaf, showing the airspaces.
Breathing- pore or stoma at a. The palisade cells which chiefly conuin the chlorophyll are at b. Epidermal cells at c.
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
S6
LEAVES— STRUCTURE OR ANATOMY 8/
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 moisture 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 (i) simple, as on primula, geranium, naegelia; (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 {^Primula 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) are small openiftgs or pores in the epidermis of leaves and soft stems that allow the passage of air and other gases and vapourr, {stomate or stoma, singular ; stomates or stomata, plural). They are placed 7iear the large intercellular spaces of the mesophyll, usually in positions least affected by direct
SS 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 (Oslerhout). showing compound guard-cells.
chlorophyll. In Fig. 1 1 5 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
Peony I3j790 None
Holly 63,600 None
Lilac 160,000 None
Mistletoe 200 200
Tradescantia 2,000 2,000
Garden Flag (iris) iIjS72 ii>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 ^ ^
OF GERANIUM LEAF, mcthod of Opening is as follows : The
LEAVES— STKUCTURE OR ANATOMY
89
P
%
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 condi- 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.
Lenticels. — On the young woody twigs of many plants (marked in osiers, cherry, birch) there are small corky spots or eleva- tions known as lenticels ( Fig. 117). They mark the loca- tion of some loose cork cells that function as stomates, for greeji 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: the lenticels are successors to the stomates. The stomates lie in the epi-
FiG. 117. — Len- ticels on Young Shoot OF Red Osier
(CORNUS).
$6 BEClNNEJiS* 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 layer of corky cells is com- pleted over the surface of the stem where the leaf is 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 of 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 9I
Suggestions. — To 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 on a 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 two sources from which to secure food, *— the air and the soil. When a plant is thoroughly dried in an oven, the water passes off ; this 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 cojttained 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 lo per cent and sometimes less than i per cent. Water is the most abundant single constituent or substance of plants. In a 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 carbon, the ash present being so small 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 bii7'ned in air. It does not go off alone, but in combination with oxygen in the form of carbon dioxide gas, COo.
The green plant secures its carbon from the air. In other words, much of the solid ynatter 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 air. 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." It 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 Hving matter.
94
BEGINNERS ' . BOTA NY
Chlorohyll ("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 groivn 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 off. How
LEAVES-^FUNCTION OB WOBK 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 idtimate 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 {CqH.iqOq)„. 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 COg + 6 parts H.O == CeH^g^e + 6 Oo). 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 like 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 sohible form, tJiis luatcrial is ready to be used in growth, either in tlie leaf, in the stem, or in the roots. With other more complex products it is then distributed throughojit all the growing parts . of the plant ; and when passing
' ; down to the root, it seems to pass
more readily through the inner bark, 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 grozving season to be nsed in the next sea- son. If a tree is constricted or strangled by a wire around its trunk (Fig. ii8), the digested food cannot readily pass down and it is stored above the girdle, causing an enlargement.
Assimilation. — TJie 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. ^'jy This upward- moving water is conducted largely through certain tubular canals of the young luood. 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
Fig, I i8. — Trunk Girdled BY A Wire. See Fig. 85.
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. Protoplasm is the living matter in pla7its. 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 need oxygen for respiration^ as anifnals do. We 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, all 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
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; hut 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, attd this surplus water passes from 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 sttfficient 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 is due to the loss of water from the cells. The cell walls are soft, and collapse. A toy balloon will not stand alone until it is inflated with air or liquid. In the woody parts of the plant the cell walls may be stiff enough to support themselves, even though the cell is empty. Measure the contraction due to wilt- ing and drying by tracing a fresh leaf on page of note- book, and then tracing the same leaf after it has been dried between papers. The softer the leaf, the greater will be the contraction.
Storage. — We have said that starch may be stored in tv/igs to be used the following year. The very early flowers on fruit trees, especially those that come before the leaves, and those that come from bulbs, as crocuses and tulips, are supported by the starch or other food that was organ- ized the year before. Some plants have very special stor- age reservoirs, as the potato, in this case being a thickened stem although growing underground. (Why a thickened stem.!* p. 84.) It is well to make the starch test on winter twigs and on all kinds of thickened parts, as tubers and bulbs.
Carnivorous Plants. — Certain plants capture insects and other very small animals and utilize them to some extent as food. Such are the sundew, which has on the leaves
lOO
BE GINNEKS' B O TAN Y
sticky hairs that close over :he insect; the Venus 's fly-trap of the Southern States, in which the halves of the leaves
close over the prey like the jaws of a steel trap ; and the various kinds of pitcher plants that col- lect insects and other organic matter in deep, water-filled, flask- like leaf pouches (Fig. 1 19).
The sundew and the Venus 's fly-trap are sensitive to contact. Other plants are sensitive to the touch without being insectivo- rous. The common cultivated sensitive plant is an example. This is readily grown from seeds (sold by seedsmen) in a warm place. Related wild plants in the south are sensitive. The utility of this sensitiveness is not understood.
Parts that Simulate Leaves. — We have learned that leaves are endlessly modified to suit the conditions in which the plant is placed. The most marked modifications are in adaptation to light. On the other hand, other organs often perform the fmtctions of leaves. Green shoots function as leaves. These shoots may look like leaves, in which case they are called cladophylla. The foliage of common asparagus is made up of fine branches : the real morpho- logical leaves are the minute dry functionless scales at the bases of these branchlets. (What reason is there for calling them leaves!*) The broad ** leaves" of the florist's smilax are cladophylla. Where are the leaves on this plant } In most of the cacti, the entire plant body performs the func- tions of leaves until the parts become cork-bound.
Fig. 119. —The Common Pitcher Plant {Sarracenia
purpurea) showingr the tubular leaves and the odd, longp-stalked flowers.
LEAVES— FUNCTION OR WORK
lOI
Leaves are sometimes modified to perform other functions than the vital processes: they may be tendrils, as the terminal leaflets of pea and sweet pea; or spines, as in barberry. Not all spines and thorns, however, represent modified leaves: some of them (as of hawthorns, osage orange, honey locust) are branches.
Suggestions. — To test for chlorophyll. 84. Purchase about a gill of wood alcohol. Secure a leaf of geranium, clover, or other plant that has been exposed to sunlight for a few hours, and, after dipping it for a minute in boiling water, put it in a white cup with sufficient alcohol to cover. Place the cup in a shallow pan of hot water on the stove where it is not hot enough for the alcohol to take fire. After a time the chlorophyll is dissolved by the alcohol which has become an intense green. Save this leaf for the starch experiment (Exercise 85). Without chlorophyll, the plant cannot appropriate the carbon dioxide of the air. Starch and photosynthesis. 85- Starch is present in the green leaves which have been exposed to sunlight; but in the dark no starch can be formed from carbon dioxide. Apply iodine to the leaf from which the chlorophyll was dissolved in the previous experiment. Note that the leaf is coloured purplish-brown throughout. The leaf contains starch. 86- Se- cure a leaf from a plant which has been in the dark for about two days. Dissolve the chlorophyll as before, and attempt to stain this leaf with iodine. No purplish-brown colour is pro- duced. This shows that the starch manufactured in the leaf may be entirely removed during darkness. 87. Secure a plant which has been kept in darkness for twenty-four hours or more. Split a small cork and pin the two halves on opposite sides of one of the leaves, as shown in Fig. 120. Place the plant in the sunlight again. After a morning of bright sunshine dissolve the chlorophyll in this leaf with alcohol; then stain the leaf with the iodine. Notice that the leaf is stained deeply except where the cork was; there sunlight and carbon dioxide were excluded, Fig. 121. There is no starch in the
Fig. I20. — Exclud- ing Light and CO2 FROM Part OF A Leaf.
Fig. 121.— The Result.
I02
BEGINNERS' BOTANY
covered area. 88. Plants or parts of plants that have developed no chlorophyll can form no starch. Secure a variegated leaf of coleus, ribbon grass, geranium, or of any plant showing both white and green areas. On a day of bright sunshine, test one of these leaves by the alcohol and iodine method for the presence of starch. Observe that the parts devoid of green colour have formed no starch. However, after starch has once been formed in the leaves,
it may be to be again the living
changed into soluble substances and removed, converted into starch in certain other parts of tissues. To test the gnmig off of oxygen by day. 89. Make the experiment illus- trated in Fig. 12 2. Under a fun- nel in a deep glass jar containing fresh spring or stream water place fresh pieces of the common waterweed elodea (or anacharis). Have the funnel considerably smaller than the vessel, and sup- port the funnel well up from the bottom so that the plant can more readily get all the carbon dioxide available in the water. Why would boiled water be undesirable in this experiment? For a home-made glass funnel, crack the bottom off a narrow-necked bottle by press- ing a red-hot poker or iron rod against it and leading the crack around the bottle. Invert a test- tube over the stem of the fun- nel. In sunlight bubbles of oxygen will arise and collect in the test-tube. If a sufficient quantity of oxygen has collected, a lighted taper inserted in the tube will glow with a brighter flame, showing the presence of oxygen in greater quantity than in the air. Shade the vessel. Are bubbles given off? For many reasons it is impracticable to continue this experiment longer than a few hours. 90. A simpler experiment may be made if one of the waterweeds Cabomba (water-lily family) is available. Tie a imniber of branches together so that the basal ends shall make a smdll bundle. Place these in a large vessel of spring water, and insert a test-tube of water as before over the bundle. The bubbles will arise from the cut surfaces. Observe the bubbles on pond scum and water- weeds on a bright day. To illustrate the results of respiration
Fig. 122. — To show the Escape OF Oxygen.
LEAVES— FUNCTION OR WORK
103
Fig. 123. — To ILLUS- TRATE A Product OF Respiration.
Fig. 124. — Respira- tion OF Thick Roots.
(CO2). 91. In a jar of germinating seeds (Fig. 123) place carefully a small dish of limewater and cover tightly. Put a similar dish in
another jar of about the
same air space. After a few
hours compare the cloudi- ness or precipitate in the
two vessels of limewater.
92. Or, place a growing
plant in a deep covered
jar away from the Hght,
and. after a few hours in- sert a lighted candle or
splinter. 93. Or, perform
a similar experiment with
fresh roots of beets or
turnips (Fig. 124) from
which the leaves are mostly
removed. In this case, the jar need not be kept dark ; why ? To test transpiration. 94. Cut a succulent shoot of any plant, thrust the end of it through a hole in a cork, and stand it in a small bottle of water. Invert over this a fruit jar, and observe that a mist soon accumulates on the inside of the glass. In time drops of water form. 95. The ex- periment may be varied as shown in Fig. 125. 96. Or, invert the fruit jar over an entire plant, as shown in Fig. 126, taking care to cover the soil with oiled paper or rubber cloth to prevent evaporation from the soil. 97. The test may also be made by placing the pot, properly protected, on bal- Fig. 121;. —To illusprate Transpiration,
I04
BEGINNERS' BOTANY
ances, and the loss of weight will be noticed (Fig. 127). 98. Cut a winter twig, seal the severed end with wax, and allow the twig to lie several days. It shrivels. There must be some upward movement of water even in winter, else plants would shrivel and die. 99. To illustrate sap pressure. The upward movement of sap water often takes place under considerable force. The cause of this force, known as root pressure^ is not well understood. The pressure varies with different plants and under different conditions. To illustrate : cut off a strong-growing ^:;^^
small plant near the ground. By means of a bit of rubber tube attach a glass tube with a bore of approxi- mately the diame- ter of the stem. Pour in a little water. Observe the rise of the water due to the pressure from be- low (Fig 128). Some plants yield a large amount of water under a pressure sufficient to raise a column several feet ; others force out Httle, but under consider- able pressure (less easily de- monstrated). The vital pro- cesses {i.e., the life processes). 100. The pupil having studied roots, stems, and leaves, should now be able to de- scribe the main vital functions of plants : what is the root func- tion? stem function? leaf function? 101. What is meant by the "sap"? 102. Where and how does the plant secure its water? oxygen? car- yig. 128. —To snov; bonf hydrogen i nitrogcMi ? sulpWur .^ potassium^ Sap PREiJSURE.
Fig. 126. — To illustrate Transpiration.
ITG. 127 — Loss OF Water.
LEAVES— FUNCTION OR WORK
los
.alcium? iron? phosphorus? 103. Where is all the starch in the world made? What does a starch-factory establishment do? Where are the real starch factories ? 104. In what part of the twenty-four hours do plants grow most rapidly in length? When is food formed and stored most rapidly? 105. Why does corn or cotton turn yellow in a long rainy spell? 106. If stubble, corn stalks, or cotton stalks are burned in the field, is as much plant-food returned to the soil as when they are ploughed under? 107. What process of plants is roughly analogous to perspiration of ani- mals? 108. What part of the organic world uses raw mineral for food ? 109. Why is earth banked over celery to blanch it? 110. Is the amount of water transpired equal to the amount absorbed? HI. Give some reasons why plants very close to a house may not thrive or may even die. 112. Why are fruit-trees pruned or thinned out as in Fig. 129? Proper balance be- tween fop and roof, 113. We have learned that the leaf parts and the root parts work together. They may be said to balance each other in activities, the root supplying pjQ^ ^^^ _ p^^ Apple the top and the top supplying the root tree, with suggestions (how?). If half the roots were cut from as to pruning when it a tree, we should expect to reduce the top is set in the orchard. At also, particularly if the tree is being trans- ''J^ "^^°^^ * P'^""^'^ planted. How would you prune a tree or °^* bush that is being transplanted? Fig. 130 may be suggestive.
Fig. 129. — Before and after Pruning.
CHAPTER XIV
DEPENDENT PLANTS
Thus far we have spoken of plants that have roots and foliage and that depend on themselves. They collect the raw materials and make them over into assimilable food. They are independent. Plants without green foliage can- not make food ; they must have it made for them or they die. They are dependent. A sprout from a potato tuber in a dark cellar cannot collect and elab- orate carbon dioxide. It lives on the food stored . ,, , r in the tuber.
Fig. 131. — A Mush ROOM, example of a sapro- phytic plant. This is the edible cultivated All plmits witJl fiatU-
"^"'^'^°°"^- rally white or blanched
parts are dependent. Their leaves do not develop. They live on organic matter — that which has been made by a plant or elaborated by an animal. The dodder, Indian pipe, beech drop, coral root among flower-bearing plants, also mushrooms and other fungi (Figs. 131, 132) are exam- ples. The dodder is common in swales, being conspicuous late in the season from its thread-Uke yellow or orange stems spreading over the herbage of other plants. One kind attacks alfalfa and is a bad pest. The seeds germin- ate in the spring, but as soon as the twining stem a:-
106
DEPENDENT PLANTS
107
Fig. 132.— a Parasitic Fungus, magnified. The mycelium, or vegetative part, is shown by the dotted- shaded parts ramify- ing in the leaf tissue. The rounded haus- toria projecting into the cells are also shown. The long fruiting parts of the fungus hang from the under surface of the leaf.
taches itself to another plant, the dod- der dies away at the base and becomes wholly dependent. It produces flowers in clusters and seeds itself freely (Fig. 133).
Parasites and Saprophytes. — A plant that is dependent on a living plant or animal is a parasite, and the plant or animal on which it lives is the host. The dodder is a true parasite ; so are the rusts, mildews, and other fungi that attack leaves and shoots and injure them.
The threads of a parasitic fungus usually creep through the intercellular spaces in the leaf or the stem and send suckers (or haustoria) into the cells (Fig. 132). The threads (or the hy- phae) clog the air-spaces of the leaf and often plug the stomates, and they also appropriate and disorganize the cell fluids ; thus
they injure or kill their host. The mass of hyphae of a fungus is called mycelium. Some of the hyphae finally grow out of the leaf and produce spores or reproductive cells that an- swer the purpose of seeds in distrib- uting the plant (b, Fig. 132).
A plant that lives on dead or de- caying matter is a saprophyte. Mush- rooms (Fig. 131) are examples; they live on the decaying matter in the dodder in soil. Mould on bread and cheese is an Fruit.
io8
BEGINNERS' BOTANY
example. Lay a piece of moist bread on a plate and invert a tumbler over it. In a few days it will be mouldy. The spores were in the air, or perhaps they had already fallen on the bread but had not had opportunity to grow. Most green plants are unable to make any direct use of the humus or vegetable mould in the soil, for they are not
saprophytic. The shelf- fungi (Fig. 134) are sap- rophytes. They are com- mon on logs and trees. Some of them are perhaps partially parasitic, extend- ing the mycelium into the wood of the living tree and causing it to become black-hearted (Fig. 134). Some parasites spring from the ground, as other plants do, but they are parasitic on the roots of their hosts. Some para- sites may be partially parasitic and partially sap7'opJiytic. Many (per- haps most) of these ground saprophytes are aided in securing their food by soil fungi, which spread their delicate threads over the root-like branches of the plant and act as intermedi- aries between the food and the saprophyte. These fungus- covered roots are known as mycorrhizas (meaning " fungus root"). Mycorrhizas are not peculiar to saprophytes. They are found on many wholly independent plants, as,
Fig. 134. — Tinder Fungus {Pofyporus igniarius) on beech log. The external part of the fungus is shown below ; the heart-rot injury above.
DEPENDENT PLANTS
109
Fig. 135. — Bacteria of Several Forms, much magnified.
for example, the heaths, oaks, apples, and pines. It is probable that the fungous threads perform some of the offices of root-hairs to the host. On the other hand, the fungus obtains some nourishment from the host. The association seems to be mutual.
Saprophytes break down or decompose or- ganic substances. Chief of these saprophytes are many microscopic organ- isms known as bacteria (Fig. 135). These innumerable organisms are immersed in water or in dead animals and
plants, and in all manner of moist organic products. By breaking down organic combinations, they produce decay. Largely through their agency, and that of many true but microscopic fungi, all things pass i?ito soil and gas. Thus are the bodies of plants and animals removed and the continuing round of life is maintained. Some parasites are green- leaved. Such is the mistle- toe (Fig. 136). They anchor themselves on the host and absorb its juices, but they also appropriate and use
Fig. 136. — American Mistletoe growing on a Walnut Branch.
no BEGINNERS' BOTANY
the carbon dioxide of the air. In some small groups of bacteria a process of organic synthesis has been shown to take place.
Epiphytes. — To be distinguished from the dependent plants are those that grow on other plants without taking food from them. These are green-leaved plants whose roots burrow in the bark of the host plant and perhaps derive some food from it, but which subsist chiefly on materials that they secure from air dust, rain water, and the air. These plants are epiphytes (meaning "upon plants") or air plants.
Epiphytes abound in the tropics. Certain orchids are among the best known examples (Fig. 37). The Spanish moss or tillandsia of the South is another. Mosses and lichens that grow 6n trees and fences may also be called epiphytes. In the struggle for existence, the plants probably have been driven to these special places in which to find opportunity to grow. Plants grow where they must, not where they will.
Suggestions. — 114. Is a puffball a plant ? Why do you think so? 115. Are mushrooms ever cultivated, and where and how? 116. In what locations are mushrooms and toadstools usually found? (There is really no distinction between mush- rooms and toadstools. They are all mushrooms.) 117. What kinds of mildew, blight, and rust do you know? 118. How do farmers overcome potato blight? Apple scab? Or any other fungous "plant disease"? 119. How do these things injure plants? 120. What is a plant disease? 121. The pupil should know that every spot or injury on a leaf or stem is caused by something, — as an insect, a fungus, wind, hail, drought, or other agency. How many uninjured or perfect leaves are there on the plant growing nearest the schoolhouse steps? 122. Give formula for Bordeaux mixture and tell how and for what it is used.
CHAPTER XV
WINTER AND DORMANT BUDS
A bud is a growing point, terminating an axis either long or short, or being the starting point of an axis. All branches spring from buds. In the growing season the bud is active ; later in the season it ceases to increase the axis in length, and as winter approaches the growing point becomes more or less thickened and covered by pro- tecting scales, in preparation for the long resting season. This resting, dormant, or winter body is what is commonly spoken of as a "bud." A winter bud may be defined as an inactive covered growing pointy waiting for spring.
Structurally, a dormant bud is a shortened axis or branch, bearing miniature leaves or flowei's or bothy and protected by a covering. Cut in two, lengthwise, a bud of the horse-chestnut or other plant that has large buds. With a pin separate
the tiny leaves. Count them.
Examine the big bud of the
rhubarb as it Hes under the
ground in late winter or early
spring ; or the crown buds of
asparagus, hepatica, or other
early spring plants. Dis- sect large buds of the apple
and pear (Figs. 137, 138). The bud is protected by firm and dry scales. These scales are modified leaves. The scales fit close. Often
Fig. 137. — Bud OF Apricot, showing the miniature leaves.
Fig. 138.- Bud OF Pear, showing both leaves and flowers. The latter are the lit- tle knobs in the centre.
Ill
112
BEGINNERS* BOTANY
the bud is protected by varnish (see horse-chestnut and the balsam poplars). Most winter buds are more or less woolly. Examine some of them under a lens. As we might expect, bud coverings are most prominent in cold and dry cHmates. Sprinkle water on velvet or flannel, and note the result and give a reason.
All winter buds give rise to branches, not to leaves alone; that is, the leaves are borne on the lengthening axis. Sometimes the axis, or branch, remains very short, — so short that it may not be noticed. Sometimes it grows several feet long.
Whether the bra7ich grows large or not depends on the chance it has, — position on the plant, soil, rainfall, and many other factors. The new shoot is the unfolding and enlarging of the tiny axis and leaves that we saw in the bud. If the conditions are congenial, the shoot may form more leaves than were tucked away in the bud. The length of the shoot usu- ally depends more on the length of the internodes than on the number of leaves.
Where Buds are. — Buds are borne in the axils of the leaves, — in the acute angle that the leaf makes with the stem. When the leaf is growing in the summer, a bud is forming above it. When the leaf falls, the bud remains, and a scar marks the place of the leaf. Fig. 139 shows the large leaf-scars of ailanthus. Observe those on the horse-chestnut, maple, apple, pear, basswood, or any other tree or bush.
Sometimes two or more buds are borne in one axil ; the extra ones are accessory or supernumerary buds. Observe them in the Tartarian honeysuckle (common in yards),
Fig. 139. — Leaf- scars. — Ailanthus
WINTER AND DORMANT BUDS
113
walnut, butternut, red maple, honey locust, and sometimes in the apricot and peach.
If the bud is at the end of a shoot, however short the shoot, it is called a terminal bud. It continues the growth of the axis in a direct line. Very often three or more buds are clustered at the tip (Fig. 140); and in this case there may be more buds than leaf scars. Only one of them, however, is strictly terminal.
A bud in the axil of a leaf is an axillary or lateral bud. Note that there is normally at least one bud in the axil of every leaf on a tree or shrub in late summer and fall. The axillary buds, if they grow, are the starting points of new shoots the following season. If a leaf is pulled off early in summer, what will become of the young bud in its axil.? Try this.
Bulbs and cabbage heads may be likened to buds ; that is, they are condensed stems, with scales or modified leaves
densely overlapping and forming a rounded body (Fig. 141). They differ from true buds, how- ever, in the fact that they are con- densations of whole main stems rather
than embryo stems Fig. 141. — a Gigantic Bud. — Cabbage. . Mr
borne m the axils of
leaves. But bulblets (as of tiger lily) may be scarcely dis- tinguishable from buds on the one hand and from bulbs
Fig. 140. — TER- MINAL Bud BETWEEN TWO
OTHER Buds. — Currant.
114
BEGINNERS' BOTANY
on the other. Cut a cabbage head in two, lengthwise, and see what it is like.
The buds that appear on roots are unusual or abnormal,
— they occur only occasionally and in no definite order.
Buds appearing in unusual places on any part of the plant
are called adventitious buds. Such usually are the buds
that arise when a large limb is cut off, and
from which suckers
or water sprouts
arise.
How Buds Open. — When the bud swells, the scales are pushed apart, the little axis elon- gates and pushes out. In most plants the outside scales fall very soon, leaving a little ring of scars. With terminal buds, this ring marks the end of the year's growth. How? Notice peach, apple, plum, willow, and other plants. In some others, all the scales grow for a time, as in the pear (Figs. 142, 143, 144). In other plants the inner bud scales become green and almost leaf-like. See the maple and hickory.
Sometimes Flowers come out of the Buds. — Leaves may or may not accompany the flowers. We saw the embryo flowers in Fig. 138. The bud is shown again in Fig. 142. In Fig. 143 it is opening. In Fig. 145
Fig. 142. — Fruit-bud OF Pear.
Fig. 143. — The opening of THE Pear Fruit-bud.
Fig. 144.— Open- ing Pear Leaf-bud.
Fig. 145. — Open- ing OF THE
Pear-bud.
WINTER AND DORMANT BUDS
115
it is more advanced, and the woolly unformed flowers are appearing. In Fig. 146 the growth is more advanced.
Fig. 146.— a sin- gle Flower IN THE Pear
CLUSTER, as seen at 7 A.M. on the day of its opening. At 10 o'clock it will be fully ex- panded.
Fig. 147. — The opening of THE Flower- bud OF Apricot.
Fig. /i4^ ^ Apricot FLOwfelf-BUD, enlarged.
leaf-buds.
Buds that contain or produce only leaves are Those which contain only flowers are flower
buds or fruit-buds. The latter occur on peach, almond, apricot, and many very early spring-flowering plants. The single flower is emerging from the apricot bud in Fig. 147. A longi- tudinal section of this bud, enlarged, is shown in Fig. 148. Those that contain both leaves and flowers are mixed buds, as in pear, apple, and most late spring- flowering plants.
Fruit buds are usually thicker or stouter than leaf-buds. They are borne in different positions on different plants. In some plants (apple, pear) they are on the ends of short branches or spurs; in others (peach, red maple) they are
along the sides of the last year's
° ^ Fig. 149. —Fruit-buds
growths. In Fig. 149 are shown and Leaf-buds of pear.
Ii6
BEGINNERS' BOTANY
three fruit-buds and one leaf-bud on E, and leaf-buds on A, See also Figs. 150, 151, 152, 153, and explain.
Fig. 150. — Fruit-buds of Apple ON Spurs: a dormant bud at the top.
Fig. 151. — Clus- ter OF Fruit- buds OF SWEET
Cherry, with one pointed leaf-bud in cen- tre.
Fig. 152. — Two Fruit-buds OF Peach with a leaf- bud between.
Fig. 153. — Opening of Leaf-buds and Flower-buds of Apple.
^^The burst of spring'' means in large part the opening of the buds. Everything was made ready the fall before. The embryo shoots and flowers were tucked aivay, and the food was stored. The warm rain falls, and the shutters open and the sleepers wake.
Arrangement of Buds. — We have found that leaves are usually arranged in a definite order ; buds are borne in the axils of leaves : therefore buds miist exhibit phyllotaxy.
WINTER AND DORMANT BUDS WJ
Moreover, branches grow from buds: branches, therefore, should show a definite arrangement. Usually, however, they do not show this arrangement because not all the buds grow and not all the branches live. (See Chaps. II and III.) It is apparent, however, that the mode of arrangement of buds determines to some extent the form of the tree. Com- pare bud arrangement in pine or fir with that in maple or apple.
Fig. 154, — Oak Spray. How are the leaves borne with reference to the annual growths ?
The uppermost buds on any twig, if they are well matured, are usually the larger and stronger and they are the most likely to grow the next spring; therefore, branches tend to be arranged in tiers (particularly well marked in spruces and firs). See Fig. 154 and explain it.
Winter Buds show what has been the Effect of Sunlight. — Buds are borne in the axils of the leaves, and ihe si&e or the vigour df the leaf determines to a large extent the size of the hud. Notice that, in most instances, the largest buds are nearest the tip (Fig. 157). If • the largest buds are not near the tip, there is some special reason for it. Can you state it ? Examine the shoots on trees and bushes.
Il8 BEGINNERS' BOTANY
Suggestions. — Some of the best of all observation lessons are those made on dormant twigs. There are many things to be learned, the eyes are trained, and the specimens are everywhere accessible. 123. At whatever time of year the pupil takes up the study of branches, he should look for three things : the ages of the various parts, the relative positions of the buds and the leaves, the different sizes of similar or comparable buds. If it is late in spring or early in summer, he should watch the development of the buds in the axils, and he should determine whether the strength or size of the bud is in any way related to the size and the vigour of the subtending (or supporting) leaf. The sizes of buds should also be noted on leafless twigs, and the sizes of the former leaves may be inferred from the size of the leaf-scar below the bud. The pupil should keep in mind the fact of the struggle for food and light, and its effects on the developing buds. 124. The bud and the branch. A twig cut from an apple tree in early spring is shown in Fig. 155. The most hasty obser- vation shows that it has various parts, or members. It seems to be divided at the point / into two parts. It is evident that the part from/ to h grew last year, and that the part below/ grew two years ago. The buds on the two parts are very unlike, and these differences challenge investigation. — In order to under- stand this seemingly lifeless twig, it will be necessary to see it as it looked late last summer (and this condition is shown in Fig. 156). The part from / to h, — which has just completed its growth, — is seen to have its leaves growing singly. In every axil (or angle which the leaf makes when it joins the shoot) is a bud. The leaf starts first, and as the season advances the bud forms in its axil. When the leaves have fallen, at the approach of winter, the buds remain, as seen in Fig. 155. Every bud on the last year's growth of a winter twig, therefore, marks the position occupied by a leaf when the shoot was growing. — The part below /, in Fig. 156, shows a wholly different arrangement. The leaves are two or more together {aaaa)y and there are buds without leaves {bbbb) . A year ago this part looked like the present shoot from f to hy — that is, the leaves were single, with a bud in the axil of each. It is now seen that some of these bud-like parts are longer than others, and that the longest ones are those which have leaves. It must be because of the leaves that they have increased in length. The body c has lost its leaves through some accident, and its growth has ceased. In other words, the parts at aaaa are like the shoot ///, except that they are shorter, and they are of the same age. One grew from the end or terminal bud of the main branch, and the others from the side or lateral buds. Parts or bodies that bear leaves are, therefore, branches. «— Tb^ buds at bbbb have no leaves, and they remain the same
WINTER AND DORMANT BUDS
119
size that they were a year ago. They are dormant. The only way for a mature bud to grow is by making leaves for itself, for a leaf
Fig. 155. — An Apple Twig.
Fig. 156.— - Same twig before leaves fell.
will never stand below it again. The twig, therefore, has buds of two ages, — those at M^ s^re two seasons old, and those on th^
120 BEGINNERS' BOTANY
tips, of all the branches {aaaa, h), and in the axil of every leaf, are one season old. It is only the terminal buds that are not axillary. When the bud begins to grow and to put forth leaves, it gives rise to a branch, which, in its turn, bears buds. — It will now be interesting to determine why certain buds gave rise to branches and why others remained dormant. The strongest shoot or branch of the year is the terminal one {fh). The next in strength is the uppermost lateral one, and the weakest shoot is at the base of the twig. The dormant buds are on the under side (for the twig grew in a horizontal position). All this suggests that those buds grew which had the best chance, — the most sunlight and room. There were too many buds for the space, and in the struggle for existence those that had the best oppor- tunities made the largest growth. This struggle for existence began a year ago, however, when the buds on the shoot below/ were forming in the axils of the leaves, for the buds near the tip of the shoot grew larger and stronger than those near its base. The growth of one year, therefore, is very largely determined by the conditions under which the buds were formed the previous year. Other dud characters. 125. It is easy to see the swelling of the budr in a room in winter. Secure branches of trees and shrubs, two to three feet long, and stand them in vases or jars, as you would flowers. Renew the water frequently and cut off the lower ends of the shoots occasionally. In a week or two the buds will begin to swell. Of red maple, peach, apricot, and other very early-flowering things, flowers may be obtained in ten to twenty days. 126. The shape, size, and colour of the winter buds are different in every kind of plant. By the buds alone botanists are often able to distinguish the kinds of plants. Even such similar plants as the different kinds of willows have good bud characters. 127. Distinguish and draw fruit-buds of apple, pear, peach, plum, and other trees. If different kinds of maples grow in the vicinity, secure twigs of the red or swamp maple, and the soft or silver maple, and compare the buds with those of the sugar maple and the Norway maple. What do you learn?
Fig. 157. — Buds of the Hickory,
CHAPTER XVI BUD PROPAGATION
We have learned (in Chap. VI) that plants propagate by means of seeds. They also propagate by means of bud parts ^ — as roots toe ks {rhizomes)y roots y runners ^ layers ^ bulbs. The pupil should determine how any plant in which he is interested naturally propagates itself (or spreads its kind). Determine this for raspberry, blackberry, strawberry, June- grass or other grass, nut-grass, water hly, May apple or mandrake, burdock, Irish potato, sweet potato, buckwheat, cotton, pea, corn, sugar-cane, wheat, rice.
Plants may be artificially propagated by similar means, as by layerSy cuttingSy and grafts. The last two we may discuss here.
Cuttings in General. — A bit of a plant stuck into the grotmd stands a cJiance of growing ; and this bit is a cutting. Plants have preferences, however, as to the kind of bit which shall be used, but tJicre is no way of telling what this preference is except by trying. In some instances this prefer- ence has not been discovered, and we say that the plant cannot be propagated by cuttings.
Most plants prefer that the cutting be made of the soft or growing parts (called "wood" by gardeners), of which the "slips" of geranium and coleus are examples. Others grow equally well from cuttings of the hard or mature parts or wood, as currant and grape; and in some instances this mature wood may be of roots, as in the blackberry. In some cases cuttings are made of tubers, as in the Irish
121
122
BEGINNERS' BOTANY
potato (Fig. 60). Pupils should make cuttings now and then. If they can do nothing more, they can make cut tings of potato, as the farmer does; and they can plant them in a box in the window.
The Softwood Cutting. — The softwood cutting is made from tissue that is still growing, or at least from that which is not dormant. It comprises one or two joints ^ with
Fig. 158. — Geranium Cutting.
Fig. 159. — Rose Cutting.
a leaf attached (Figs. 158, 159). It must not be allowed to wilt. Therefore, it must be protected fro^n direct sun- light and dry air until it is ivell established ; and if it has many leaves ^ some of them shotdd be removed, or at least cut in twOy in order to reduce the evaporating sjcrface. The soil should be uniformly moist. The pictures show the depth to which the cuttings are planted.
For most plants, the proper age or maturity of wood for the making of cuttings may be determined by giving the twig a quick bend: if it snaps and hangs by the bark, it is in proper condition; if it bends without breaking, it is too young and soft or too old ; if it splinters, it is too old and woody. The tips of strong upright shoots usually make the best cuttings. Preferably, each cutting should have a joint or node near its base; and if the internodes are very short it may comprise two or three joints.
BUD PROPAGATION
123
Fig. 160. — Cutting-box.
Tlie st£m of the cutting is inserted one third or more of its lengtJi in clean sand or gravel, and the earth is pressed firmly about it. A newspaper may be laid over the bed to ex- clude the light — if the sun strikes it — and to prevent too rapid evaporation. The soil should be moist clear through, not on top only.
Loose sandy or gravelly soil is nsed. Sand used by masons is good material in which to start most cuttings; or fine gravel — sifted of most of its earthy matter — may be used. Soils are avoided which contain much decay- ing organic matter, for these soils are breeding places of fungi, which attack the soft cutting and cause it to " damp off," or to die at or near the surface of the ground. If the cuttings are to be grown in a window, put three or four inches of the earth in a shallow box or a pan. A soap box cut in two lengthwise, so that it makes a box four or five inches deep — as a gardener's fiat — is excellent (Fig. 160). Cuttings of common plants, as geranium, coleus,
fuchsia, carnation, are kept at a living-room temperature. As long as the cuttings look bright and green, they are in good condition. It may be a month before roots form. When roots have formed, the plants begin to make new leaves at the tip. Then they may be transplanted into other boxes or into pots. The verbena in Fig, 161 is just ready for transplanting.
Fig. 161. — Verhena Cutting ready for transplanting.
124
BEGINNERS* BOTANY
Fig. 162.— Old Geranium Plant cut back to make it throw out Shoots from which Cuttings can be made.
dow plants are those which old. The geranium aiid fuchsia cut- tings which are made in Januaryy February y or MarcJi will give compact blooming plants for the 7text winter; and thereafter 7iew ones should take their places (Fig.
163).
The Hardwood Cutting. — Best re- sults with cuttings of mature wood are
It is not always easy to find growing shoots from which to make the cut- tings. The best practice, in that case, is to cut back an old pi ant y then keep it wann and well watered^ and thereby force it to throw out new shoots. The old geranium plant from the window garden, or the one taken up from the lawn bed, may be treated this way (see Fig. 162). The best plants of geranium and coleus and most win- are not more than one year
Fig. 163.-
Early Winter Geranium, from a spring cutting.
BUD PROPAGATION
125
secured when the cuttings are made in the fall and then buried until spring in sand ift the cellar. These cuttings are usually six to ten inches long. They are not idle while they rest. The lower end calluses or heals, and the roots form more readily when the cutting is planted in the spring. But if the proper season has passed, take cuttings at any time in winter, plant them in a deep box in the window, and watch. They will need no shading or special care. Grape, currant, gooseberry, willow, and poplar readily take root from the hardwood. Fig. 164 shows a currant cutting. It has only one bud above the ground.
The Graft. — When the cutting is inserted in a plant rather than in the soil, it is a graft ; and the graft may grow. In this case the cutting grows fast to the other plant, and the two become one. When the cutting is inserted in a plant, it is no longer called a cutting but a scion ; and the plant in which it is inserted is called the stock. Fruit trees are grafted in order that a ce7'tain variety or kind may be per- petuated, as a Baldwin or Ben Davis vari- ety of apple, Seckel or Bartlett pear, Navel or St. Michael orange.
Plants have preferences as to the stocks on which they will grow ; but zve can find out ivJiat their choice is only by making the experiment. The pear grows well on the quince, but the quince does not thrive on the pear. The pear grows on some of the hawthorns, but it is an unwilling subject on the apple. Tomato plants will grow on potato plants and potato plants on tomato plants.
I
I
Fig. 164. — Cur- rant CUTIING.
126 BEGINNERS* BOTANY
When the potato is the root, both tomatoes and potatoes may be produced, although the crop will be very small; when the tomato is the root, neither potatoes nor tomatoes will be produced. Chestnut will grow on some kinds of oak. In general, one species or kind is grafted on the same species, as apple on apple, pear on pear, orange on orange.
The forming, growing tissue of the stem (on the plants we have been discussing) is the cambium (Chap. X), lying on the ontside of the woody cy Haider beneath the bark. In order that union may take place, the camhium of the scion and of the stock must come together. Therefore the scion is set in the side of the stock. There are many ways of shaping the scion and of preparing the stock to receive it. These ways are dictated largely by the relative sizes of scion and stock, although many of them are matters of personal preference. The underlying principles are two: securing close contact between the cambiums of scion and stock; covering the ivounded surfaces to prevent evapora- tion and to protect the parts from disease.
On large stocks the commonest form of grafting is the cleft-graft. The stock is cut off and split; and in one or both sides a wedge-shaped scion is firmly inserted. Fig. 165 shows the scion; Fig. 166, the scions set in the stock; Fig. 167^ the stock waxed. It wall be seen that the lower bud — that lying in the wedge — is covered by the wax; but being nearest the food supply and least exposed to weather, it is the most likely to grow : it will push through the wax.
Cleft-grafting is practised in spring, as growth begins. The scions are cut previously, when perfectly dormant, and from the tree which it is desired to propagate. The scions are kept in sand or moss in the cellar. Limbs of various
BUD PROPAGATION
127
sizes may be cleft-grafted, — from a half inch up to four inches in diameter; but a diameter of one to one and a half inches is the most convenient size. All the leading or main branches of a tree top may be grafted. If the remaining parts of the top are gradually cut away and the scions grow well, the entire top will be changed over to the new variety.
Fig. 165.—
SciOIsf OF
Apple.
Fig. 166.— The Scion Inserted.
Fig. 167.— The Paris Waxed.
Another form of grafting is known as budding. In this case a single bud is used, and it is sHpped underneath the bark of the stock and securely tied (not waxed) with soft material, as bass bark, corn shuck, yarn, or raffia (the last a commercial palm fibre). Budding is performed when the bark of the stock will slip or peel (so that the bud can be inserted), and when the bud is mature ejiougJi to grow. Usually budding is performed in late summer or early fall, when the winter buds are well formed ; or it may be practised in spring with buds cut in winter. In ordinary summer budding (which is the usual mode) the *'bud" or scion forms a union with the stock, and then lies dormant till the following spring, as if it were still on its own twig.
128
BEGINNERS' BOTANY
Budding is mostly restricted to young trees in the nursery. In the spring following the budding, the stock is cut off just above the bud, so that only the shoot from the bud grows to make the future tree. This prevailing form of J budding (shield-budding) is shown in Fig.
\i 168.
^ t Suggestions. — 128. Name the plants that the
■ I gardener propagates by means of cuttings.