TRANSCRIBER’S NOTE

Some minor changes to the text are noted at the end of the book.

BEGINNERS’ BOTANY

THE MACMILLAN COMPANY
NEW YORK · BOSTON · CHICAGO
SAN FRANCISCO
MACMILLAN & CO., Limited
LONDON · BOMBAY · CALCUTTA
MELBOURNE
THE MACMILLAN CO. OF CANADA, Ltd.
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 all teaching of plants and animals to beginners, the plants themselves and the animals themselves should be made the theme, rather than any amount of definitions and of mere study in books. Books will be very useful in guiding the way, in arranging the subjects systematically, and in explaining obscure points; but if the pupil does not know the living and growing plants when he has completed his course in botany, he has not acquired very much that is worth the while.

It is well to acquaint the beginner at first with the main features of the entire plant rather than with details of its parts. He should at once form a mental picture of what the plant is, and what are some of its broader adaptations to the life that it leads. In this book, the pupil starts with the entire branch or the entire plant. It is sometimes said that the pupil cannot grasp the idea of struggle for existence until he knows the names and the uses of the different parts of the plant. This is an error, although well established 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 discussing osmosis; but the minute explanations would mean nothing to the beginner and their use would tend to confuse 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. 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 advanced to another. It is neither necessary nor desirable to safeguard statements to the beginner by such qualifications 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 importance 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 knowledge and the affairs of his time, may be of less educative value than the learning of a trade in a shop. We are beginning to learn that the ideals and the abilities should be developed out of the common surroundings and affairs of life rather than imposed on the pupil as a matter of abstract unrelated theory.

It is much better for the beginning pupil to acquire a real conception of a few central principles and points of view respecting common forms that will enable him to tie his knowledge together and organize it and apply it, than to familiarize himself with any number of mere facts about the lower forms of life which, at the best, he can know only indirectly and remotely. If the pupil wishes to go farther in later years, he may then take up special groups and phases.

CONTENTS

BEGINNERS’ BOTANY

CHAPTER I
NO TWO PLANTS OR PARTS ARE ALIKE

Fig. 1.—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 standard type.

If one compares any two branches or twigs on a tree, it will be found that they differ in size, age, form, vigour, and in other ways (Fig. [1]).

If one compares any two leaves, it will be found that they are unlike in size, shape, colour, veining, hairiness, markings, cut of the margins, or other small features. In some cases (as in Fig. [2]) the differences are so great as to be readily seen in a small black-and-white drawing.

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 discover the differences, remembering that nothing in nature is so small or apparently trivial as to be overlooked.

Fig. 2.—No Two Leaves are Alike.

Variation, or differences between organs and also between 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 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 measure 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 personal 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 observation 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 conditions. 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 in Fig. [1] probably had more room and a better exposure to light than the smaller ones. Probably no two of the leaves in Fig. [2] are equally exposed to light, or enjoy identical advantages in relation to the food that they receive from the tree.

Fig. 3.—A Battle for Life.

Examine any tree to determine under what advantages or disadvantages any of the limbs may live. Examine similarly the different plants in a garden row (Fig. [3]); or the different bushes in a thicket; or the different trees in a wood.

The plant meets its conditions by succumbing 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 herbaceous 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 providing 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 expanding 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.

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 animal is placed is called its environment, that is, its surroundings. 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 environment, 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. I). Note that some are large and strong and that these stand farthest toward light and room. Some are very small and weak, barely able to live under the competition. Some have died. The pupil can easily determine which of the dead branches perished first. He should take note of the position or place of the branch on the tree, and determine whether the greater part of the dead twigs are toward the centre of the tree top or toward the outside of it. Determine whether accident has overtaken any of the parts. 3. Let the pupil examine the top of any thick old apple tree, to see whether there is any struggle for existence and whether any limbs have perished. 4. If the pupil has access to a forest, let him determine why there are no branches on the trunks of the old trees. Examine a tree of the same kind growing in an open field. 5. A row of lettuce or other plants sown thick will soon show the competition between plants. Any fence row or weedy place will also show it. Why does the farmer destroy the weeds among the corn or potatoes? How does the florist reduce 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 offspring 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 variation; that is, if plants were perfectly rigid or invariable (all exactly alike) they could not meet new conditions. Conditions are necessarily new for every organism. It is impossible to picture a perfectly inflexible and stable succession of plants or animals.

Breeding.—Man is able to modify plants and animals. All our common domestic animals are very unlike their original ancestors. So all our common and long-cultivated 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 common black-cap raspberry with its common wild ancestor, or the cultivated blackberry with the wild form.

Fig. 5.—Desirable and Undesirable Types of Cotton Plants. Why?

By choosing seeds from a plant that pleases him, the breeder may be able, under given conditions, to produce numbers of plants with more or less of the desired qualities; 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 continuously choosing the most suitable plants is known as selection. A somewhat similar process proceeds in wild nature, and it is then known as natural selection.

Fig. 6.—Flax Breeding.
A is a plant grown for seed production;
B for fibre production. Why?

Fig. 7.—Breeding.

A, effect from breeding from smallest grains (after four years), average head; B, result from breeding from the plumpest and heaviest grains (after four years), average head.

Suggestions.—6. Every pupil should undertake at least one simple experiment in selection of seed. He may select kernels from the best plant of corn in the field, and also from the poorest plant,—having reference not so much to mere incidental size and vigour of the plants that may be due to accidental conditions in the field, as to the apparently constitutional strength and size, number of ears, size of ears, perfectness of ears and kernels, habit of the plant as to suckering, and the like. The seeds may be saved and sown the next year. Every crop can no doubt be very greatly improved by a careful process of selection extending over a series of years. Crops are increased in yield or efficiency in three ways: better general care; enriching the land in which they grow; attention to breeding.

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 obliged to grow, they 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 aggregations of plants that are adapted to similar general conditions 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 conveniently be associated chiefly with the moisture supply, as: wet-region societies, comprising aquatic and bog vegetation (Fig. [8]); arid-region societies, comprising desert and most sand-region vegetation; 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. With reference to altitude, societies might be classified as lowland (which are chiefly wet-region), intermediate (chiefly mid-region), subalpine or mid-mountain (which are chiefly boreal), alpine or high-mountain.

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 growing in natural conditions. There are roadside, fence-row, lawn, thicket, pasture, dune, woods, cliff, barn-yard societies. Every different place has its characteristic vegetation. 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.

Fig. 8.—A Wet-region Society.

Some Details of Plant Societies.—Societies may be composed of scattered and intermingled plants, or of dense clumps or groups of plants. Dense clumps or groups are usually made up of one kind of plant, and they are then 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.

Fig. 9.—A Mid-region Society.

In a large newly cleared area, plants usually first establish themselves in dense colonies. Note the great patches 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 recently worked highway. The competition amongst themselves and with their neighbours finally breaks up the colonies, and a mixed and intermingled flora is generally the result.

In many parts of the world the general tendency of neglected areas is to run into forest. All plants rush for the 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 unobserved here and there in the tangle, and in the slow processes 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.

Fig. 10.—Overgrowth and Undergrowth in Three Series,—trees, bushes, grass.

Some plants associate. They grow together. This is possible largely because they diverge or differ in character. Plants associate in two ways: by growing side by side; by growing above or beneath. In sparsely populated societies, plants may grow alongside each other. In most cases, however, there is overgrowth and undergrowth: one kind grows beneath another. Plants that have become 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 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 societies. The knoll which is cool with grass and strawberries 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 September, find the dead stalks of the flora of May. What succeeds 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 landscape 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 distinguishes 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 autumn colour is associated with the natural maturity and death of the leaf, but it is most brilliant in long and open 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 by frost. Because of the long, dry falls and the great variety of plants, the autumnal colour of the American landscape is phenomenal.

Ecology.—The study of the relationships of plants and animals to each other and to seasons and environments is known as ecology (still written œcology in the dictionaries). It considers the habits, habitats, and modes of life of living 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 instruction in botany is the study of plant societies. It adds definiteness and zest to excursions. 7. Let each excursion be confined to one or two societies. Visit one day a swamp, another day a forest, another a pasture or meadow, another a roadside, another a weedy field, another a cliff or ravine. Visit shores whenever possible. Each pupil should be assigned a bit of ground—say 10 or 20 ft. square—for special study. He should make a list showing (1) how many kinds of plants it contains, (2) the relative abundance of each. The lists secured in different regions should be compared. 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 endeavour 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 of several distinct parts. The most prominent of these parts are root, stem, leaf, flower, fruit, and seed. Familiar plants differ wonderfully in size and shape,—from fragile mushrooms, delicate waterweeds and pond-scums, to floating leaves, soft grasses, coarse weeds, tall bushes, slender climbers, gigantic trees, and hanging moss.

The Stem Part.—In most plants there is a main central part or shaft on which the other or secondary parts are borne. This main part is the plant axis. Above ground, in most plants, the main plant axis bears the branches, leaves, and flowers; below ground, it bears the roots.

The rigid part of the plant, which persists over winter and which is left after leaves and flowers are fallen, is the framework of the plant. The framework is composed of both root and stem. When the plant is dead, the framework remains for a time, but it slowly decays. The dry winter stems of weeds are the framework, or skeleton of the plant (Figs. [11 and 12]). The framework of trees is the most conspicuous part of the plant.

The Root Part.—The root bears the stem at its apex, but otherwise it normally bears only root-branches. The stem, however, bears leaves, flowers, and fruits. Those living surfaces of the plant which are most exposed to light are green or highly coloured. The root tends to grow downward, but the stem tends to grow upward toward light 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. The flowers always precede the fruits and seeds. Many plants die when the seeds have matured. The whole mass of leaves of any plant or any branch is known as its 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 embraces various stages, or epochs, as dormant seed, germination, growth, flowering, fruiting. Some plants run their course in a few weeks or months, and some live for centuries.

The entire life period of a plant is called a generation. It is the whole period from birth to normal death, without reference to the various stages or events through which it passes.

A generation begins with the young seed, not with germination. It 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 sunflower; 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, bleeding heart, violet, water-lily, 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 is, false annuals). Of such are lily, crocus, onion, potato, and bull nettle.

True annuals reach old age the first year. Plants which are normally perennial may become annual in a shorter-season climate by being killed by frost, rather than by dying naturally at the end of a season of growth. They are climatic annuals. Such plants are called plur-annuals in the short-season region. Many tropical perennials are plur-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.

Fig. 13.—A Shrub or Bush. Dogwood osier.

Woody or ligneous plants usually live longer than herbs. Those that remain low and produce several or 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 kind; and, as far as we can see, this is the end for which the plant itself lives. The seed or spore is the final product of the plant.

Fig. 14.—A Tree. The weeping birch.

Suggestions.—8. The teacher may assign each pupil to one plant in the school yard, or field, or in a pot, and ask him to bring out the points in the lesson. 9. The teacher may put on the board the names of many common plants and ask the pupils to classify into annuals, pseud-annuals, plur-annuals (or climatic annuals), biennials, perennials, herbaceous perennials, ligneous perennials, herbs, bushes, trees. Every plant grown on the farm should be so classified: wheat, oats, corn, buckwheat, timothy, strawberry, raspberry, currant, tobacco, alfalfa, flax, crimson clover, hops, cowpea, field bean, sweet potato, peanut, radish, sugar-cane, barley, cabbage, and others. Name all the kinds of trees you know.

CHAPTER VI
SEEDS AND GERMINATION

The seed contains a miniature plant, or embryo. The embryo usually has three parts that have received names: the stemlet, or caulicle; the seed-leaf, or cotyledon (usually 1 or 2); the bud, or plumule, lying between or above the cotyledons. These parts are well seen in the common bean (Fig. [15]), particularly when the seed has been soaked for a few hours. One of the large cotyledons—comprising half of the bean—is shown at R. The caulicle is at O. The plumule is shown at A. The cotyledons are attached to the caulicle at F: this point may be taken as the first node or joint.

Fig. 15.— Parts of the Bean.

R, cotyledon; O, caulicle; A, plumule; F, first node.

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 dicotyledons, although really forming a different group.

These two groups—the dicotyledons and the monocotyledons—represent two great natural divisions of the vegetable kingdom. The dicotyledons contain the woody 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.

Fig. 16.—External Parts of Bean.

Every seed is provided with food to support the germinating plant. Commonly this food is starch. The food may be stored in the cotyledons, as in bean, pea, squash; or outside the cotyledons, as in castor bean, pine, Indian corn. When the food is outside or around the embryo, it is usually called endosperm.

Seed-coats; Markings on Seed.—The embryo and endosperm 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 the pollen-tube entered the forming ovule and through which the caulicle breaks in germination. The micropyle is shown at M in Fig. [16]. The scar where the seed broke from its funiculus (or stalk that attached it to its pod) is named the hilum. It occupies a third of the length of the bean in Fig. [16]. The hilum and micropyle are always present in seeds, but they are not always close together. In many cases it is difficult to identify the micropyle in the dormant seed, but its location is at once shown by the protruding caulicle as germination begins. Opposite the micropyle in the bean (at the other end of the hilum) is an elevation known as the raphe. 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 unfounded.

Germination.—The embryo is not dead; it is only dormant. 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 gradually the plantlet secures a foothold in the soil and gathers food for itself. When the plantlet is finally able to shift for itself, 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 (CO₂).

Fig. 17.—Pea. Grotesque forms assumed when the roots cannot gain entrance to the soil.

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 direction of the young hypocotyl, or emerging caulicle, is downwards. As soon as roots form, it becomes fixed and its subsequent growth tends to raie the cotyledons above the ground, as in the bean. When cotyledons rise into the 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 germination is hypogeal (“beneath the earth”). Pea and scarlet runner bean are examples (Fig. [48]). When the germinating seed lies on a hard surface, as on closely compacted 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 cotyledons 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.

Fig. 18.—Cotyledons of Germinating Bean spread apart to show Elongating Caudicle and Plumule.

Fig. 19.—Germination of Bean.

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 hypocotyl, or elongated caulicle, emerges, the plumule leaves have begun to enlarge, 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, and the plant straightens and the cotyledons expand. These cotyledons, or “halves of the bean,” persist for some time (b, 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.

Fig. 20.—Sprouting of Castor Bean.

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 germinating seed, however, it will be found that the cotyledons are contained inside a fleshy body, or sac (a, Fig. [21]). This sac is the endosperm. Against its inner surface the thin, veiny cotyledons are very closely pressed, absorbing its substance (Fig. [22]). The cotyledons increase in size as they reach the air (Fig. [23]), and become functional leaves.

Germination of Monocotyledons.—Thus far we have studied dicotyledonous seeds; we may now consider the monocotyledonous 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 single cotyledon is at a, the caulicle at b, the plumule at p. The cotyledon remains in the seed. The food is stored both in the cotyledon and as endosperm, chiefly the latter. The emerging shoot is the plumule, with a sheathing leaf (p, 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 epicotyl elongates, particularly if 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-sheath, c, m; the epicotyl has grown to p; the first plumule-leaf is at o.

Fig. 27.—Indian Corn.

o, plumule; n to p, epicotyl.

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.

Fig. 28.—Germination is Complete.

p, top of epicotyl; o, plumule-leaf; m, roots; c, lower roots.

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 gymnosperm.

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 whirling motion by the shape of the wing? Repeat the experiment 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 experiments?

Fig. 29.—Cones of Hemlock (above), White Pine, Pitch Pine.

Suggestions.—Few subjects connected 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 specimens 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 different 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 experiment 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 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 germination 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 germination 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.

Fig. 30.—Muskmelon Seedlings, with the unlike seed-leaves and true leaves.

14. Make the tests described in the introductory experiments with bean, corn, the castor bean, and other seed for starch and proteids. Test flour, oatmeal, rice, sunflower, four o’clock, various nuts, and any other seeds obtainable. Record your results by arranging the seeds in three classes, 1. Much starch (colour blackish or purple), 2. Little starch (pale blue or greenish), 3. No starch (brown or yellow). 15. Rate of growth of seedlings as affected by differences in temperature. Pack soft wet paper to the depth of an inch in the bottom of four glass bottles or tumblers. Put ten soaked peas or beans into each. Cover each securely and set them in places having different temperatures that vary little. (A furnace room, a room with a stove, a room without stove but reached by sunshine, an unheated room not reached by the sun). Take the temperatures occasionally with the thermometer to find difference in temperature. The tumblers in warm places should be covered very tightly to prevent the germination from being retarded by drying out. Record the number of seeds which sprout in each tumbler within 1 day, 2 days, 3 days, 4 days, etc. 16. Is air necessary for the germination and growth of seedlings? Place damp blotting paper in the bottom of a bottle and fill it three-fourths full of soaked seeds, and close it tightly with a rubber stopper or oiled cork. Prepare a “check experiment” by having another bottle with all conditions the same except that it is covered loosely that air may have access to it, and set the bottles side by side (why keep the bottles together?). Record results as in the preceding experiment. 17. What is the nature of the gas given off by germinating seeds? Fill a tin box or large-necked bottle with dry beans or peas, then add water; note how much they swell. Secure two fruit jars. Fill one of them a third full of beans and keep them moist. Allow the other to remain empty. In a day or two insert a lighted splinter or taper into each. In the empty jar the taper burns: it contains oxygen. In the seed jar the taper goes out: the air has been replaced by carbon dioxide. The air in the bottle may be tested for carbon dioxide by removing some of it with a rubber bulb attached to a glass tube (or a fountain-pen filler) and bubbling it through lime water. 18. Temperature. Usually there is a perceptible rise in temperature in a mass of germinating seeds. This rise may be tested with a thermometer. 19. Interior of seeds. Soak seeds for twenty-four hours and remove the coat. Distinguish the embryo from the endosperm. Test with iodine. 20. Of what utility is the food in seeds? Soak some grains of corn overnight and remove 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 the experiment.) Peas or beans may be sprouted on damp blotting paper; the cotyledons of one may be removed, and this with a normal seed equally advanced in germination may be placed on a perforated cork floating in water in a jar so that the roots extend into the water. Their growth may be observed for several weeks. 21. Effect of darkness on seeds and seedlings. A box may be placed mouth downward over a smaller box in which seedlings are growing. The empty box should rest on half-inch blocks to allow air to reach the seedlings. Note any effects on the seedlings of this cutting off of the light. Another box of seedlings not so covered may be used as a check. Lay a plank on green grass and after a week note the change that takes place beneath it. 22. Seedling of pine. Plant pine seeds. Notice how they emerge. Do the cotyledons stay in the ground? How many cotyledons have they? When do the cotyledons get free from the seed-coat? What is the last part of the cotyledon to become free? Where is the growing point or plumule? How many leaves appear at once? Does the new pine cone grow on old wood or on wood formed the same spring with the cone? Can you always find partly grown cones on pine trees in winter? Are pine cones when mature on two-year-old wood? How long do cones stay on a tree after the seeds have fallen out? What is the advantage of the seeds falling before the cones? 23. Home experiments. If desired, nearly all of the fore-going experiments may be tried at home. The pupil can thus make the drawings for the notebook at home. A daily record of measurements of the change in size of the various parts of the seedling should also be made.

Fig. 31.—A Home-made Seed-tester.

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 blotting 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 given seeds would require out of doors, or 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 percentage 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 mounted 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 arrangement 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 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 dissecting-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.

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.

The entire mass of roots of any plant is called its root system. The root system may be annual, biennial or perennial, 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 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 extend strongly and the side roots develop until finally the tap-root character disappears.

Fig. 34.—A Buttercup Plant, with fibrous roots.

Shape and Extent of the Root System.—The depth to which roots extend depends on the kind of plant, and the nature 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 food, 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 definite form as the stem has. Roots are usually very crooked, because they are constantly turned aside by obstacles. Examine roots in stony soil.

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.

Fig. 35.—The Bracing Base of a Field Pine.

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.

Aërial Roots.—Although roots usually grow underground, there are some that naturally grow above ground. These usually occur on climbing plants, the roots becoming supports or fulfilling the office of tendrils. These aërial roots usually turn away from the light, and therefore enter the 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. 36.—Aërial Roots of Trumpet Creeper or Tecoma.

Fig. 37.—Aërial Roots of an Orchid.

In some plants all the roots are aërial; 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 familiar examples are some of the tropical orchids which are grown in glass-houses (Fig. [37]). Rootlike organs of dodder and other parasites are discussed in a future chapter.

Some plants bear aërial 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 overhanging branches (and from the fruits) into the shallow water, and thereby gradually marches into the sea. The tangled mass behind catches the drift, and soil is formed.

Fig. 38.—Indian Corn, showing the brace roots at oo.

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. Cuttings of the stems of roses, figs, geraniums, and other plants, when planted, send out adventitious 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 themselves as stems and leaves do. Each kind of plant has its own form or habit of root (Fig. [39]). Carefully wash away the soil from the roots of any two related plants, as oats and wheat, and note the differences in size, depth, direction, mode of branching, number of fibrils, colour, and other 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.

Fig. 39.—Roots of Barley at A and Corn at B.
Carefully trace the differences.

Roots differ not only in their form and habit, but also in colour of tissue, character of bark or rind, and other features. It is excellent practice to try 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 materials. The first function is considered in Chapter VII; we may now give attention in more detail to the second.

Fig. 40.—Wheat growing under Different Soil Treatments. Soil deficient in nitrogen; commercial nitrogen applied to pot 3 (on right).

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 hold-fasts 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 of fertilizers. Certain substances, as common salt, will kill the roots.

Fig. 41.—Nodules on Roots of Red Clover.

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 mineral substances, as compounds of potassium, 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.

Fig. 42.—Nodules on Vetch.

Nitrogen enters through the Roots.—All plants must have nitrogen; yet, although about four-fifths of 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 elements, 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 uncombined nitrogen and pass it on to the plant. The nitrogen 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 fertilizers, the use of leguminous crops to plough under is a very important agricultural practice in preparing the land for other crops. In order that leguminous crops may acquire atmospheric nitrogen more freely and thereby thrive better, the land is sometimes sown or inoculated with the nodule-forming bacteria.

Fig. 43.—Two Kinds of Soil that have been Wet and then Dried. The loamy soil above remains loose and capable of growing plants; the clay soil below has baked and cracked.

Roots require moisture in order to serve the plant. The soil water that is valuable to the plant is not the free water, but the thin 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 surrounding 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 “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.

Fig. 44.—Root-hairs of the Radish.

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 soil, and this suffocation of the roots is very soon apparent in the general ill health of the plant. Stirring or tilling the soil aërates it. Water plants and bog plants have adapted themselves 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 fine divisions, are clothed with the root-hairs (Figs. [44], [45], [46]). These root-hairs attach to the soil particles, and a great amount of soil is thus brought into actual contact with the plant. These are very delicate prolonged surface cells of the roots. They are borne for a short distance just back of the tip of the root.

Fig. 45.—Cross-section of Root, enlarged, showing root-hairs.

Rootlet and root-hair differ. The rootlet is a compact cellular structure. The root-hair is a delicate tubular cell (Fig. [45]), within which is contained living matter (protoplasm); and the protoplasmic lining membrane of the wall governs the entrance of water and substances in solution. Being long and tube-like, these root-hairs are especially adapted for taking in the largest quantity of solutions; and they are the principal means by which plant-food is absorbed from the soil, although the surfaces of the rootlets themselves do their part. Water plants do not produce an abundant system of root-hairs, and such plants depend largely on their rootlets.

Fig. 46.—Root-hair, much enlarged, in contact with the soil particles (s). Air-spaces at a; water-films on the particles, as at w.

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 germinated 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 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 lining 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 secondary roots are sometimes called tertiary roots. Do the secondary 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]) surrounded 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-like 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 cylinder, cortex, and epidermis. Notice the hard cap on the tip of roots. Roots differ from stems in having no real pith.

Fig. 47.—Growing Point of Root of Indian Corn.

d, d, cells which will form the epidermis; p, p, cells that will form bark; e, e, endodermis; pl, cells which will form the axis cylinder; i, initial group of cells, or growing point proper; c, root-cap.

Microscopic Structure of Roots.—Near the end of any young root or shoot the cells are found to differ from one another more or less, according to the distance from the point. This differentiation takes place in the region just back of the growing point. To study growing points, use 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 rectangular 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 slight differences in the tissues a short distance back of the growing point. There are four regions: the central cylinder, made up of several rows of cells in the centre (pl); the endodermis, (e) composed of a single layer on each side which separates the central cylinder from the bark; the cortex, or inner bark, (e) of several 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 studied by the pupil beginning near the growing point and going upward, 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.

Fig. 48.—The Marking of the Stem and Root.

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 subdividing, are very delicate and are easily injured. The cells forming the root-cap are older and tougher and are suited for pushing aside the soil that the root may penetrate 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 root can be determined. Give a reason why a root cannot elongate throughout its length,—whether there is anything to prevent a young root from doing so.

Fig. 49.—The Result.

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 toward the earth, even if the seed is planted with the micropyle up. This phenomenon is called positive geotropism. Stems grow away from the earth. This is negative geotropism.

Suggestions (Chaps. VII and VIII).—25. Tests for food. Examine 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 distance 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 flattened when they come in contact with grains of sand.

Fig. 50.—The Grasp of a Plant on the Particles of Earth. A grass plant pulled in a garden.

28. Root hold of plant. The pupil should also study the root hold. Let him carefully pull up a plant. If a plant grows alongside a fence or other rigid object, he may test the root hold by securing a string to the plant, letting the string hang over the fence, and then adding 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; place in a cool cellar; after some days 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.

Fig. 51.—Plant growing in Inverted Pot.

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 effect of gravity 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?

Fig. 52.—Holes in Soil made by Roots, now decayed. Somewhat magnified.

35. Soil texture. Carefully turn up soil in a rich garden or field so that you have unbroken lumps as large as a hen’s egg. Then break these lumps apart carefully with the fingers and 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 another lump from a clay bank or pile where no plants have been growing. Is there any difference 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 out till it wilts; then add water and note the rapidity with which it recovers. Vary the experiment in quantity of water applied. Does the plant call for water sooner when it stands in a sunny window 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 sealing-wax, chewing-gum, or paste, stick a quill about three inches long to the smaller end of the egg. 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 bottle? 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 buds, leaves, flowers, and fruits. Its office is to 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 appearance 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 working parts; the stem merely connects them, and its form is exceedingly variable.

Kinds of Stems.—The stem may be so short as to 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; but 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 conspicuous stems. These so-called stemless plants die to the ground every year.

Fig. 55.—Trailing Stem of Wild Morning Glory (Convolvulus arvensis).

Stems are erect when they grow straight up (Figs. [53, 54]). They are trailing when they run along on the ground, as melon, wild morning-glory (Fig. [55]). They are creeping when they run on the ground and take root at places, as the strawberry. They are decumbent when they flop 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 climbing when they cling to other objects for support (Figs. [36],[ 56]).

Fig. 56.—A Climbing Plant (a twiner).

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 deliquescent. The branches arise from one 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 always grow to a single stem or trunk, pear 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 genealogy 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 between 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 grow 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. 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 growing 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 elongate by growing more or less throughout the young or soft part or “between joints” (Figs. [48],[ 49]). But any part 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, the trunk or woody parts never grow longer or higher; branches do not become farther apart or higher from the ground.

Fig. 60.—Sprouts arising from the Buds, or eyes, of a potato tuber.

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 direction of any limb (Chap. II). This is well illustrated in any tree or bush that grows against a building or on the margin 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.

Fig. 61.—Cracking of the Bark on an Elm Branch.

The stem is cylindrical, the outer part being bark and the inner part being wood or woody tissue. In the dicotyledonous plants, the bark is usually easily separated from the remainder of the cylinder 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 outside of the plant cylinder. It is evident, then, that the covering of bark must expand in order to allow of the expansion of the woody cylinder within it. The tissues, 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. [61] shows that the outer layers of bark (which are long since dead, and serve only as protective tissue) have reached the limit 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 cylindrical, and why the old bark becomes marked with furrows, scales, and plates.

Fig. 62.—Piece of Bark from an Old Elm Trunk.

Most woody plants increase in diameter by the addition of an annual layer or “ring” on the outside of the woody cylinder, underneath the bark. The monocotyledonous 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 reason, the bark should become so dense and strong that the trunk cannot expand, the tree is said to be “bark-bound.” Such condition is not rare in orchard trees that have been neglected. When good tillage is given to such trees, they 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 softening 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, filling 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 significance—whether the tree has ever been released, or injured by natural agencies.

Fig. 63.—Proper Cutting of a Branch. The wound will soon be “healed.”

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 regular. 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 difference in the rapidity of the healing process in different kinds of trees. Compare the apple tree and the peach. This tissue may in 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.

Fig. 64.—Erroneous Pruning.

The callus grows from the living 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 branches 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 healing tissue. The end of the remaining stub is merely covered over by the callus, and usually remains a dead piece of wood sealed inside the trunk (Fig. [65]). If wounds do not heal over speedily, 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 (Fig. [66]).

Fig. 65.—Knot in a Hemlock Log.