GRAY'S LESSONS IN BOTANY
REVISED EDITION

THE
ELEMENTS OF BOTANY

FOR BEGINNERS AND FOR SCHOOLS

By ASA GRAY

IVISON, BLAKEMAN, AND COMPANY
NEW YORK AND CHICAGO

Copyright,
By Asa Gray.
1887.

PREFACE.

This volume takes the place of the author's Lessons in Botany and Vegetable Physiology, published over a quarter of a century ago. It is constructed on the same lines, and is a kind of new and much revised edition of that successful work. While in some respects more extended, it is also more concise and terse than its predecessor. This should the better fit it for its purpose now that competent teachers are common. They may in many cases develop paragraphs into lectures, and fully illustrate points which are barely, but it is hoped clearly, stated. Indeed, even for those without a teacher, it may be that a condensed is better than a diffuse exposition.

The book is adapted to the higher schools, "How Plants Grow and Behave" being the "Botany for Young People and Common Schools." It is intended to ground beginners in Structural Botany and the principles of vegetable life, mainly as concerns Flowering or Phanerogamous plants, with which botanical instruction should always begin; also to be a companion and interpreter to the Manuals and Floras by which the student threads his flowery way to a clear knowledge of the surrounding vegetable creation. Such a book, like a grammar, must needs abound in technical words, which thus arrayed may seem formidable; nevertheless, if rightly apprehended, this treatise should teach that the study of botany is not the learning of names and terms, but the acquisition of knowledge and ideas. No effort should be made to commit technical terms to memory. Any term used in describing a plant or explaining its structure can be looked up when it is wanted, and that should suffice. On the other hand, plans of structure, types, adaptations, and modifications, once understood, are not readily forgotten; and they give meaning and interest to the technical terms used in explaining them.

In these "Elements" naturally no mention has been made of certain terms and names which recent cryptogamically-minded botanists, with lack of proportion and just perspective, are endeavoring to introduce into phanerogamous botany, and which are not needed nor appropriate, even in more advanced works, for the adequate recognition of the ascertained analogies and homologies.

As this volume will be the grammar and dictionary to more than one or two Manuals, Floras, etc., the particular directions for procedure which were given in the "First Lessons" are now relegated to those works themselves, which in their new editions will provide the requisite explanations. On the other hand, in view of such extended use, the Glossary at the end of this book has been considerably enlarged. It will be found to include not merely the common terms of botanical description but also many which are unusual or obsolete; yet any of them may now and then be encountered. Moreover, no small number of the Latin and Greek words which form the whole or part of the commoner specific names are added to this Glossary, some in an Anglicized, others in their Latin form. This may be helpful to students with small Latin and less Greek, in catching the meaning of a botanical name or term.

The illustrations in this volume are largely increased in number. They are mostly from the hand of Isaac Sprague.

It happens that the title chosen for this book is that of the author's earliest publication, in the year 1836, of which copies are rarely seen; so that no inconvenience is likely to arise from the present use of the name.

ASA GRAY.
Cambridge, Massachusetts,
March, 1887.

CONTENTS.

ELEMENTS OF BOTANY.

Section I. INTRODUCTORY.

1. Botany is the name of the science of the vegetable kingdom in general; that is, of plants.

2. Plants may be studied as to their kinds and relationships. This study is Systematic Botany. An enumeration of the kinds of vegetables, as far as known, classified according to their various degrees of resemblance or difference, constitutes a general System of plants. A similar account of the vegetables of any particular country or district is called a Flora.

[3.] Plants may be studied as to their structure and parts. This is Structural Botany, or Organography. The study of the organs or parts of plants in regard to the different forms and different uses which the same kind of organ may assume,—the comparison, for instance, of a flower-leaf or a bud-scale with a common leaf,—is Vegetable Morphology, or Morphological Botany. The study of the minute structure of the parts, to learn by the microscope what they themselves are formed of, is Vegetable Anatomy, or Histology; in other words, it is Microscopical Structural Botany. The study of the actions of plants or of their parts, of the ways in which a plant lives, grows, and acts, is the province of Physiological Botany, or Vegetable Physiology.

4. This book is to teach the outlines of Structural Botany and of the simpler parts of the physiology of plants, that it may be known how plants are constructed and adapted to their surroundings, and how they live, move, propagate, and have their being in an existence no less real, although more simple, than that of the animal creation which they support. Particularly, this book is to teach the principles of the structure and relationships of plants, the nature and names of their parts and their modifications, and so to prepare for the study of Systematic Botany; in which the learner may ascertain the name and the place in the system of any or all of the ordinary plants within reach, whether wild or cultivated. And in ascertaining the name of any plant, the student, if rightly taught, will come to know all about its general or particular structure, rank, and relationship to other plants.

5. The vegetable kingdom is so vast and various, and the difference is so wide between ordinary trees, shrubs, and herbs on the one hand, and mosses, moulds, and such like on the other, that it is hardly possible to frame an intelligible account of plants as a whole without contradictions or misstatements, or endless and troublesome qualifications. If we say that plants come from seeds, bear flowers, and have roots, stems, and leaves, this is not true of the lower orders. It is best for the beginner, therefore, to treat of the higher orders of plants by themselves, without particular reference to the lower.

[6.] Let it be understood, accordingly, that there is a higher and a lower series of plants; namely:—

Phanerogamous Plants, which come from seed and bear flowers, essentially stamens and pistils, through the co-operation of which seed is produced. For shortness, these are commonly called Phanerogams, or Phænogams, or by the equivalent English name of Flowering Plants.[1]

Cryptogamous Plants, or Cryptogams, come from minute bodies, which answer to seeds, but are of much simpler structure, and such plants have not stamens and pistils. Therefore they are called in English Flowerless Plants. Such are Ferns, Mosses, Algæ or Seaweeds, Fungi, etc. These sorts have each to be studied separately, for each class or order has a plan of its own.

7. But Phanerogamous, or Flowering, Plants are all constructed on one plan, or type. That is, taking almost any ordinary herb, shrub, or tree for a pattern, it will exemplify the whole series: the parts of one plant answer to the parts of any other, with only certain differences in particulars. And the occupation and the delight of the scientific botanist is in tracing out this common plan, in detecting the likenesses under all the diversities, and in noting the meaning of these manifold diversities. So the attentive study of any one plant, from its growth out of the seed to the flowering and fruiting state and the production of seed like to that from which the plant grew, would not only give a correct general idea of the structure, growth, and characteristics of Flowering Plants in general, but also serve as a pattern or standard of comparison. Some plants will serve this purpose of a pattern much better than others. A proper pattern will be one that is perfect in the sense of having all the principal parts of a phanerogamous plant, and simple and regular in having these parts free from complications or disguises. The common Flax-plant may very well serve this purpose. Being an annual, it has the advantage of being easily raised and carried in a short time through its circle of existence, from seedling to fruit and seed.

FOOTNOTES:

[1] The name is sometimes Phanerogamous, sometimes Phænogamous (Phanerogams, or Phænogams), terms of the same meaning etymologically; the former of preferable form, but the latter shorter. The meaning of such terms is explained in the Glossary.

Section II. FLAX AS A PATTERN PLANT.

[8.] Growth from the Seed. Phanerogamous plants grow from seed, and their flowers are destined to the production of seeds. A seed has a rudimentary plant ready formed in it,—sometimes with the two most essential parts, i. e. stem and leaf, plainly discernible; sometimes with no obvious distinction of organs until germination begins. This incipient plant is called an Embryo.

9. In this section the Flax-plant is taken as a specimen, or type, and the development and history of common plants in general is illustrated by it. In flax-seed the embryo nearly fills the coats, but not quite. There is a small deposit of nourishment between the seed-coat and the embryo: this may for the present be left out of the account. This embryo consists of a pair of leaves, pressed together face to face, and attached to an extremely short stem. (Fig. [2-4].) In this rudimentary condition the real nature of the parts is not at once apparent; but when the seed grows they promptly reveal their character,—as the accompanying figures (Fig. [5-7]) show.

Fig. 1. Pod of Flax. 2. Section lengthwise, showing two of the seeds; one whole, the other cut half away, bringing contained embryo into view. 3. Similar section of a flax-seed more magnified and divided flatwise; turned round, so that the stem-end (caulicle) of the embryo is below: the whole broad upper part is the inner face of one of the cotyledons; the minute nick at its base is the plumule. 4. Similar section through a seed turned edgewise, showing the thickness of the cotyledons, and the minute plumule between them, i. e. the minute bud on the upper end of the caulicle.

[10.] Before the nature of these parts in the seed was altogether understood, technical names were given to them, which are still in use. These initial leaves were named Cotyledons. The initial stem on which they stand was called the Radicle. That was because it gives rise to the first root; but, as it is really the beginning of the stem, and because it is the stem that produces the root and not the root that produces the stem, it is better to name it the Caulicle. Recently it has been named Hypocotyle; which signifies something below the cotyledons, without pronouncing what its nature is.

Fig. 5. Early Flax seedling; stem (caulicle), root at lower end, expanded seed-leaves (cotyledons) at the other: minute bud (plumule) between these. 6. Same later; the bud developed into second pair of leaves, with hardly any stem-part below them; then into a third pair of leaves, raised on a short joint of stem; and a fifth leaf also showing. 7. Same still older, with more leaves developed, but these singly (one after another), and with joints of stem between them.

[11.] On committing these seeds to moist and warm soil they soon sprout, i. e. germinate. The very short stem-part of the embryo is the first to grow. It lengthens, protrudes its root-end; this turns downward, if not already pointing in that direction, and while it is lengthening a root forms at its point and grows downward into the ground. This root continues to grow on from its lower end, and thus insinuates itself and penetrates into the soil. The stem meanwhile is adding to its length throughout; it erects itself, and, seeking the light, brings the seed up out of the ground. The materials for this growth have been supplied by the cotyledons or seed-leaves, still in the seed: it was the store of nourishing material they held which gave them their thickish shape, so unlike that of ordinary leaves. Now, relieved of a part of this store of food, which has formed the growth by which they have been raised into the air and light, they appropriate the remainder to their own growth. In enlarging they open and throw off the seed-husk; they expand, diverge into a horizontal position, turn green, and thus become a pair of evident leaves, the first foliage of a tiny plant. This seedling, although diminutive and most simple, possesses and puts into use, all the Organs of Vegetation, namely, root, stem, and leaves, each in its proper element,—the root in the soil, the stem rising out of it, the leaves in the light and open air. It now draws in moisture and some food-materials from the soil by its root, conveys this through the stem into the leaves, where these materials, along with other crude food which these imbibe from the air, are assimilated into vegetable matter, i. e. into the material for further growth.

[12.] Further Growth soon proceeds to the formation of new parts,—downward in the production of more root, or of branches of the main root, upward in the development of more stem and leaves. That from which a stem with its leaves is continued, or a new stem (i. e. branch) originated, is a Bud. The most conspicuous and familiar buds are those of most shrubs and trees, bearing buds formed in summer or autumn, to grow the following spring. But every such point for new growth may equally bear the name. When there is such a bud between the cotyledons in the seed or seedling it is called the Plumule. This is conspicuous enough in a bean (Fig. [29].), where the young leaf of the new growth looks like a little plume, whence the name, plumule. In flax-seed this is very minute indeed, but is discernible with a magnifier, and in the seedling it shows itself distinctly (Fig. [5, 6, 7]).

[13.] As it grows it shapes itself into a second pair of leaves, which of course rests on a second joint of stem, although in this instance that remains too short to be well seen. Upon its summit appears the third pair of leaves, soon to be raised upon its proper joint of stem; the next leaf is single, and is carried up still further upon its supporting joint of stem; and so on. The root, meanwhile, continues to grow underground, not joint after joint, but continuously, from its lower end; and commonly it before long multiplies itself by branches, which lengthen by the same continuous growth. But stems are built up by a succession of leaf-bearing growths, such as are strongly marked in a reed or corn-stalk, and less so in such an herb as Flax. The word "joint" is ambiguous: it may mean either the portion between successive leaves, or their junction, where the leaves are attached. For precision, therefore, the place where the leaf or leaves are borne is called a Node, and the naked interval between two nodes, an Internode.

Fig. 8. Upper part of Flax-plant in blossom.

14. In this way a simple stem with its garniture of leaves is developed from the seed. But besides this direct continuation, buds may form and develop into lateral stems, that is, into branches, from any node. The proper origin of branches is from the Axil of a leaf, i. e. the angle between leaf and stem on the upper side; and branches may again branch, so building up the herb, shrub, or tree. But sooner or later, and without long delay in an annual like Flax, instead of this continuance of mere vegetation, reproduction is prepared for by

[15.] Blossoming. In Flax the flowers make their appearance at the end of the stem and branches. The growth, which otherwise might continue them farther or indefinitely, now takes the form of blossom, and is subservient to the production of seed.

Fig. 9. Flax-flowers about natural size. 10. Section of a flower moderately enlarged, showing a part of the petals and stamens, all five styles, and a section of ovary with two ovules or rudimentary seeds.

[16.] The Flower of Flax consists, first, of five small green leaves, crowded into a circle: this is the Calyx, or flower-cup. When its separate leaves are referred to they are called Sepals, a name which distinguishes them from foliage-leaves on the one hand, and from petals on the other. Then come five delicate and colored leaves (in the Flax, blue), which form the Corolla, and its leaves are Petals; then a circle of organs, in which all likeness to leaves is lost, consisting of slender stalks with a knob at summit, the Stamens; and lastly, in the centre, the rounded body, which becomes a pod, surmounted by five slender or stalk-like bodies. This, all together, is the Pistil. The lower part of it, which is to contain the seeds, is the Ovary; the slender organs surmounting this are Styles; the knob borne on the apex of each style is a Stigma. Going back to the stamens, these are of two parts, viz. the stalk, called Filament, and the body it bears, the Anther. Anthers are filled with Pollen, a powdery substance made up of minute grains.

17. The pollen shed from the anthers when they open falls upon or is conveyed to the stigmas; then the pollen-grains set up a kind of growth (to be discerned only by aid of a good microscope), which penetrates the style: this growth takes the form of a thread more delicate than the finest spider's web, and reaches the bodies which are to become seeds (Ovules they are called until this change occurs); these, touched by this influence, are incited to a new growth within, which becomes an embryo. So, as the ovary ripens into the seed-pod or capsule (Fig. [1], etc.) containing seeds, each seed enclosing a rudimentary new plantlet, the round of this vegetable existence is completed.

Section III. MORPHOLOGY OF SEEDLINGS.

18. Having obtained a general idea of the growth and parts of a phanerogamous plant from the common Flax of the field, the seeds and seedlings of other familiar plants may be taken up, and their variations from the assumed pattern examined.

[19.] Germinating Maples are excellent to begin with, the parts being so much larger than in Flax that a common magnifying glass, although convenient, is hardly necessary. The only disadvantage is that fresh seeds are not readily to be had at all seasons.

Fig. 11. Embryo of Sugar Maple, cut through lengthwise and taken out of the seed. 12, 13. Whole embryo of same just beginning to grow; a, the stemlet or caulicle, which in 13 has considerably lengthened.

20. The seeds of Sugar Maple ripen at the end of summer, and germinate in early spring. The embryo fills the whole seed, in which it is nicely packed; and the nature of the parts is obvious even before growth begins. There is a stemlet (caulicle) and a pair of long and narrow seed-leaves (cotyledons), doubled up and coiled, green even in the seed, and in germination at once unfolding into the first pair of foliage-leaves, though of shape quite unlike those that follow.

21. Red Maple seeds are ripe and ready to germinate at the beginning of summer, and are therefore more convenient for study. The cotyledons are crumpled in the seed, and not easy to straighten out until they unfold themselves in germination. The story of their development into the seedling is told by the accompanying Fig. [14-20]; and that of Sugar Maple is closely similar. No plumule or bud appears in the embryo of these two Maples until the seed-leaves have nearly attained their full growth and are acting as foliage-leaves, and until a root is formed below. There is no great store of nourishment in these thin cotyledons; so further growth has to wait until the root and seed-leaves have collected and elaborated sufficient material for the formation of the second internode and its pair of leaves, which lending their help the third pair is more promptly produced, and so on.

[22.] Some change in the plan comes with the Silver or Soft White Maple. (Fig. [21-25]). This blossoms in earliest spring, and it drops its large and ripened keys only a few weeks later. Its cotyledons have not at all the appearance of leaves; they are short and broad, and (as there is no room to be saved by folding) they are straight, except a small fold at the top,—a vestige of the habit of Maples in general. Their unusual thickness is due to the large store of nutritive matter they contain, and this prevents their developing into actual leaves. Correspondingly, their caulicle does not lengthen to elevate them above the surface of the soil; the growth below the cotyledons is nearly all of root. It is the little plumule or bud between them which makes the upward growth, and which, being well fed by the cotyledons, rapidly develops the next pair of leaves and raises them upon a long internode, and so on. The cotyledons all the while remain below, in the husk of the fruit and seed, and perish when they have yielded up the store of food which they contained.

Fig. 14. One of the pair of keys or winged fruits of Red Maple; the seed-bearing portion cut open to show the seed. 15. Seed enlarged, and divided to show the crumpled embryo which fills it. 16. Embryo taken out and partly opened. 17. Embryo which has unfolded in early stage of germination and begun to grow. 18. Seedling with next joint of stem and leaves apparent; and 19 with these parts full-grown, and bud at apex for further growth. 20. Seedling with another joint of stem and pair of leaves.

23. So, even in plants so much alike as Maples, there is considerable difference in the amount of food stored up in the cotyledons by which the growth is to be made; and there are corresponding differences in the germination. The larger the supply to draw upon, the stronger the growth, and the quicker the formation of root below and of stem and leaves above. This deposit of food thickens the cotyledons, and renders them less and less leaf-like in proportion to its amount.

Fig. 21. Fruit (one key) of Silver Maple, Acer dasycarpum, of natural size, the seed-bearing portion divided to show the seed. 22. Embryo of the seed taken out. 23. Same opened out, to show the thick cotyledons and the little plumule or bud between them. 24. Germination of Silver Maple, natural size; merely the base of the fruit, containing the seed, is shown. 25. Embryo of same, taken out of the husk; upper part of growing stem cut off, for want of room.

[24.] Examples of Embryos with thickened Cotyledons. In the Pumpkin and Squash (Fig. [26, 27]), the cotyledons are well supplied with nourishing matter, as their sweet taste demonstrates. Still, they are flat and not very thick. In germination this store is promptly utilized in the development of the caulicle to twenty or thirty times its length in the seed, and to corresponding thickness, in the formation of a cluster of roots at its lower end, and the early production of the incipient plumule; also in their own growth into efficient green leaves. The case of our common Bean (Phaseolus vulgaris, Fig. [28-30]) is nearly the same, except that the cotyledons are much more gorged; so that, although carried up into the air and light upon the lengthening caulicle, and there acquiring a green color, they never expand into useful leaves. Instead of this, they nourish into rapid growth the plumule, which is plainly visible in the seed, as a pair of incipient leaves; and these form the first actual foliage.

25. Very similar is the germination of the Beech (Fig. [31-33]), except that the caulicle lengthens less, hardly raising the cotyledons out of the ground. Nothing would be gained by elevating them, as they never grow out into efficient leaves; but the joint of stem belonging to the plumule lengthens well, carrying up its pair of real foliage-leaves.

[26.] It is nearly the same in the Bean of the Old World (Vicia Faba, here called Horse Bean and Windsor Bean): the caulicle lengthens very little, does not undertake to elevate the heavy seed, which is left below or upon the surface of the soil, the flat but thick cotyledons remaining in it, and supplying food for the growth of the root below and the plumule above. In its near relative, the Pea (Fig. [34, 35]), this use of cotyledons for storage only is most completely carried out. For they are thickened to the utmost, even into hemispheres; the caulicle does not lengthen at all; merely sends out roots from the lower end, and develops its strong plumule from the upper, the seed remaining unmoved underground. That is, in technical language, the germination is hypogæous.

Fig. 26. Embryo of Pumpkin-seed, partly opened. 27. Young seedling of same.

Fig. 28. Embryo of Common Bean (Phaseolus vulgaris): caulicle bent down over edge of cotyledons. 29. Same germinating: caulicle well lengthened and root beginning; thick cotyledons partly spreading; and plumule (pair of leaves) growing between them. 30. Same, older, with plumule developed into internode and pair of leaves.

27. There is sufficient nourishment in the cotyledons of a pea to make a very considerable growth before any actual foliage is required. So it is the stem-portion of the plumule which is at first conspicuous and strong-growing. Here, as seen in Fig. [35], its lower nodes bear each a useless leaf-scale instead of an efficient leaf, and only the later ones bear leaves fitted for foliage.

Fig. 31. A Beech-nut, cut across. 32. Beginning germination of the Beech, showing the plumule growing before the cotyledons have opened or the root has scarcely formed. 33. The same, a little later, with the plumule-leaves developing, and elevated on a long internode.

Fig. 34. Embryo of Pea, i. e. a pea with the coats removed; the short and thick caulicle presented to view. 35. Same in advanced germination: the plumule has developed four or five internodes, bearing single leaves; but the first and second leaves are mere scales, the third begins to serve as foliage; the next more so.

28. This hypogæous germination is exemplified on a larger scale by the Oak (Fig. [36, 37]) and Horse-chestnut (Fig. [38, 39]); but in these the downward growth is wholly a stout tap-root. It is not the caulicle; for this lengthens hardly any. Indeed, the earliest growth which carries the very short caulicle out of the shell comes from the formation of foot-stalks to the cotyledons; above these develops the strong plumule, below grows the stout root. The growth is at first entirely, for a long time mainly, at the expense of the great store of food in the cotyledons. These, after serving their purpose, decay and fall away.

Fig. 36. Half of an acorn, cut lengthwise, filled by the very thick cotyledons, the base of which encloses the minute caulicle. 37. Oak-seedling.

Fig. 38. Half of a horse-chestnut, similarly cut; the caulicle is curved down on the side of one of the thick cotyledons. 39. Horse-chestnut in germination; foot-stalks are formed to the cotyledons, pushing out in their lengthening the growing parts.

29. Such thick cotyledons never separate; indeed, they sometimes grow together by some part of their contiguous faces; so that the germination seems to proceed from a solid bulb-like mass. This is the case in a horse-chestnut.

[30.] Germinating Embryo supplied by its own Store of Nourishment, i. e. the store in the cotyledons. This is so in all the illustrations thus far, essentially so even in the Flax. This nourishment was supplied by the mother plant to the ovule and seed, and thence taken into the embryo during its growth. Such embryos, filling the whole seed, are comparatively large and strong, and vigorous in germination in proportion to the amount of their growth while connected with the parent plant.

[31.] Germinating Embryo supplied from a Deposit outside of Itself. This is as common as the other mode; and it occurs in all degrees. Some seeds have very little of this deposit, but a comparatively large embryo, with its parts more or less developed and recognizable. In others this deposit forms the main bulk of the seed, and the embryo is small or minute, and comparatively rudimentary. The following illustrations exemplify these various grades. When an embryo in a seed is thus surrounded by a white substance, it was natural to liken the latter to the white of an egg, and the embryo or germ to the yolk. So the matter around or by the side of the embryo was called the Albumen, i. e. the white of the seed. The analogy is not very good; and to avoid ambiguity some botanists call it the Endosperm. As that means in English merely the inwards of a seed, the new name is little better than the old one; and, since we do not change names in botany except when it cannot be avoided, this name of albumen is generally kept up. A seed with such a deposit is albuminous, one with none is exalbuminous.

32. The Albumen forms the main bulk of the seed in wheat, maize, rice, buckwheat, and the like. It is the floury part of the seed. Also of the cocoa-nut, of coffee (where it is dense and hard), etc.; while in peas, beans, almonds, and in most edible nuts, the store of food, although essentially the same in nature and in use, is in the embryo itself, and therefore is not counted as anything to be separately named. In both forms this concentrated food for the germinating plant is food also for man and for animals.

Fig. 40. Seed of Morning Glory divided, moderately magnified; shows a longitudinal section through the centre of the embryo as it lies crumpled in the albumen. 41. Embryo taken out whole and unfolded; the broad and very thin cotyledons notched at summit; the caulicle below. 42. Early state of germination. 43. Same, more advanced; caulicle or primary stem, cotyledons or seed-leaves, and below, the root, well developed.

33. For an albuminous seed with a well-developed embryo, the common Morning Glory (Ipomœa purpurea, Fig. [40-43]) is a convenient example, being easy and prompt to grow, and having all the parts well apparent. The seeds (duly soaked for examination) and the germination should be compared with those of Sugar and Red Maple ([19-21]). The only essential difference is that here the embryo is surrounded by and crumpled up in the albumen. This substance, which is pulpy or mucilaginous in fresh and young seeds, hardens as the seed ripens, but becomes again pulpy in germination; and, as it liquefies, the thin cotyledons absorb it by their whole surface. It supplements the nutritive matter contained in the embryo. Both together form no large store, but sufficient for establishing the seedling, with tiny root, stem, and pair of leaves for initiating its independent growth; which in due time proceeds as in Fig. [44, 45].

Fig. 44. Seedling of Morning Glory more advanced (root cut away); cotyledons well developed into foliage-leaves: succeeding internode and leaf well developed, and the next forming. 45. Seedling more advanced; reduced to much below natural size.

34. Smaller embryos, less developed in the seed, are more dependent upon the extraneous supply of food. The figures [46-53] illustrate four grades in this respect. The smallest, that of the Peony, is still large enough to be seen with a hand magnifying glass, and even its cotyledons may be discerned by the aid of a simple stage microscope.

35. The broad cotyledons of Mirabilis, or Four-o'clock (Fig. [52, 53]), with the slender caulicle almost encircle and enclose the floury albumen, instead of being enclosed in it, as in the other illustrations. Evidently here the germinating embryo is principally fed by one of the leaf-like cotyledons, the other being out of contact with the supply. In the embryo of Abronia (Fig. [54, 55]), a near relative of Mirabilis, there is a singular modification; one cotyledon is almost wanting, being reduced to a rudiment, leaving it for the other to do the work. This leads to the question of the

[36.] Number of Cotyledons. In all the preceding illustrations, the embryo, however different in shape and degree of development, is evidently constructed upon one and the same plan, namely, that of two leaves on a caulicle or initial stem,—a plan which is obvious even when one cotyledon becomes very much smaller than the other, as in the rare instance of Abronia (Fig. [54, 55]). In other words, the embryos so far examined are all

[37.] Dicotyledonous, that is, two-cotyledoned. Plants which are thus similar in the plan of the embryo agree likewise in the general structure of their stems, leaves, and blossoms; and thus form a class, named from their embryo Dicotyledones, or in English, Dicotyledonous Plants. So long a name being inconvenient, it may be shortened into Dicotyls.

Fig. 46. Section of a seed of a Peony, showing a very small embryo in the albumen, near one end. 47. This embryo detached, and more magnified.

Fig. 48. Section of a seed of Barberry, showing the straight embryo in the middle of the albumen. 49. Its embryo detached.

Fig. 50. Section of a Potato seed, showing the embryo coiled in the albumen. 51. Its embryo detached.

Fig. 52. Section of the seed of Mirabilis or Four-o'clock, showing the embryo coiled round the outside of the albumen. 53. Embryo detached; showing the very broad and leaf-like cotyledons, applied face to face, and the pair incurved.

Fig. 54. Embryo of Abronia umbellata; one of the cotyledons very small. 55. Same straightened out.

[38.] Polycotyledonous is a name employed for the less usual case in which there are more than two cotyledons. The Pine is the most familiar case. This occurs in all Pines, the number of cotyledons varying from three to twelve; in Fig. [56, 57] they are six. Note that they are all on the same level, that is, belong to the same node, so as to form a circle or whorl at the summit of the caulicle. When there are only three cotyledons, they divide the space equally, are one third of the circle apart. When only two they are 180° apart, that is, are opposite.

39. The case of three or more cotyledons, which is constant in Pines and in some of their relatives (but not in all of them), is occasional among Dicotyls. And the polycotyledonous is only a variation of the dicotyledonous type,—a difference in the number of leaves in the whorl; for a pair is a whorl reduced to two members. Some suppose that there are really only two cotyledons even in a Pine embryo, but these divided or split up congenitally so as to imitate a greater number. But as leaves are often in whorls on ordinary stems, they may be so at the very beginning.

Fig. 56. Section of a Pine-seed, showing its polycotyledonous embryo in the centre of the albumen, moderately magnified. 57. Seedling of same, showing the freshly expanded six cotyledons in a whorl, and the plumule just appearing.

[40.] Monocotyledonous (meaning with single cotyledon) is the name of the one-cotyledoned sort of embryo. This goes along with peculiarities in stem, leaves, and flowers, which all together associate such plants into a great class, called Monocotyledonous Plants, or, for shortness, Monocotyls. It means merely that the leaves are alternate from the very first.

41. In Iris (Fig. [58, 59]) the embryo in the seed is a small cylinder at one end of the mass of the albumen, with no apparent distinction of parts. The end which almost touches the seed coat is caulicle, the other end belongs to the solitary cotyledon. In germination the whole lengthens (but mainly the cotyledon) only enough to push the proximate end fairly out of the seed; from this end the root is formed, and from a little higher the plumule later emerges. It would appear therefore that the cotyledon answers to a minute leaf rolled up, and that a chink through which the plumule grows out is a part of the inrolled edges. The embryo of Indian Corn shows these parts on a larger scale and in a more open state (Fig. [66-68]). There, in the seed, the cotyledon remains, imbibing nourishment from the softened albumen, and transmitting it to the growing root below and new-forming leaves above.

Fig. 58. Section of a seed of the Iris, or Flower-de-Luce, enlarged, showing its small embryo in the albumen, near the bottom. 59. A germinating seedling of the same, its plumule developed into the first four leaves (alternate), the first one rudimentary, the cotyledon remains in the seed.

Fig. 60. Section of an Onion seed showing the slender and coiled embryo in the albumen, moderately magnified. 61. Seed of same in early germination.

Fig. 62. Germinating Onion, more advanced, the chink at base of cotyledon opening for the protrusion of the plumule, consisting of a thread-shaped leaf. 63. Section of base of Fig. 62, showing plumule enclosed. 64. Section of same later, plumule emerging. 65. Later stage of 62, upper part cut off. 66. A grain of Indian Corn, flatwise, cut away a little, so as to show the embryo, lying on the albumen which makes the principal bulk of the seed. 67. A grain cut through the middle in the opposite direction, dividing the embryo through its thick cotyledon and its plumule, the latter consisting of two leaves, one enclosing the other. 68. The embryo taken out whole; the thick mass is the cotyledon, the narrow body partly enclosed by it is the plumule, the little projection at its base is the very short radicle enclosed in the sheathing base of the first leaf of the plumule.

Fig. 69. Grain of Indian Corn in germination, the ascending sprout is the first leaf of the plumule, enclosing the younger leaves within, at its base the primary root has broken through. 70. The same, advanced; the second and third leaves developing, while the sheathing first leaf does not further develop.

42. The general plan is the same in the Onion (Fig. [60]-[65]), but with a striking difference. The embryo is long, and coiled in the albumen of the seed. To ordinary examination it shows no distinction of parts. But germination plainly shows that all except the lower end of it is cotyledon. For after it has lengthened into a long thread, the chink from which the plumule in time emerges is seen at the base, or near it, so the caulicle is extremely short, and does not elongate, but sends out from its base a simple root, and afterwards others in a cluster. Not only does the cotyledon lengthen enormously in the seedling, but (unlike that of Iris, Indian Corn, and all the cereal grains) it raises the comparatively light seed into the air, the tip still remaining in the seed and feeding upon the albumen. When this food is exhausted and the seedling is well established in the soil, the upper end decays and the emptied husk of the seed falls away.

43. In Maize or Indian Corn (Fig. [66-70]), the embryo is more developed in the seed, and its parts can be made out. It lies against the starchy albumen, but is not enclosed therein. The larger part of it is the cotyledon, thickish, its edges involute, and its back in contact with the albumen; partly enclosed by it is the well-developed plumule or bud which is to grow. For the cotyledon remains in the seed to fulfil its office of imbibing nourishment from the softened albumen, which it conveys to the growing sprout; the part of this sprout which is visible is the first leaf of the plumule rolled up into a sheath and enclosing the rudiments of the succeeding leaves, at the base enclosing even the minute caulicle. In germination the first leaf of the plumule develops only as a sort of sheath, protecting the tender parts within; the second and the third form the first foliage. The caulicle never lengthens: the first root, which is formed at its lower end, or from any part of it, has to break through the enclosing sheath; and succeeding roots soon spring from all or any of the nodes of the plumule.

[44.] Simple-stemmed Plants are thus built up, by the continuous production of one leaf-bearing portion of stem from the summit of the preceding one, beginning with the initial stem (or caulicle) in the embryo. Some Dicotyls and many Monocotyls develop only in this single line of growth (as to parts above ground) until the flowering state is approached. For some examples, see Cycas (Fig. [71], front, at the left); a tall Yucca or Spanish Bayonet, and two Cocoa-nut Palms behind; at the right, a group of Sugar-canes, and a Banana behind.

Fig. 71. Simple-stemmed vegetation.

Section IV. GROWTH FROM BUDS: BRANCHING.

45. Most plants increase the amount of their vegetation by branching, that is, by producing lateral shoots.

46. Roots branch from any part and usually without definite order. Stems normally give rise to branches only at definite points, namely, at the nodes, and there only from the axils of leaves.

[47.] Buds (Fig. [72, 73]). Every incipient shoot is a Bud ([12]). A stem continues its growth by its terminal bud; it branches by the formation and development of lateral buds. As normal lateral buds occupy the axils of leaves, they are called axillary buds. As leaves are symmetrically arranged on the stem, the buds in their axils and the branches into which axillary buds grow partake of this symmetry. The most conspicuous buds are the scaly winter-buds of most shrubs and trees of temperate and cold climates; but the name belongs as well to the forming shoot or branch of any herb.

Fig. 72. Shoot of Horse-chestnut, of one year's growth, taken in autumn after the leaves have fallen; showing the large terminal bud and smaller axillary buds.

Fig. 73. Similar shoot of Shagbark Hickory, Carya alba.

[48.] The Terminal Bud, in the most general sense, may be said to exist in the embryo,—as cotyledons, or the cotyledons and plumule,—and to crown each successive growth of the simple stem so long as the summit is capable of growth. The whole ascending growth of the Palm, Cycas, and the like (such as in Fig. [71]) is from a terminal bud. Branches, being repetitions of the main stem and growing in the same way, are also lengthened by terminal buds. Those of Horse-chestnut, Hickory, Maples, and such trees, being the resting buds of winter, are conspicuous by their protective covering of scales. These bud-scales, as will hereafter be shown, are themselves a kind of leaves.

[49.] Axillary Buds were formed on these annual shoots early in the summer. Occasionally they grow the same season into branches; at least, some of them are pretty sure to do so whenever the growing terminal bud at the end of the shoot is injured or destroyed. Otherwise they may lie dormant until the following spring. In many trees or shrubs these axillary buds do not show themselves until spring; but if searched for, they may be detected, though of small size, hidden under the bark. Sometimes, although early formed, they are concealed all summer long under the base of the leaf-stalk, which is then hollowed out into a sort of inverted cup, like a candle-extinguisher, to cover them; as in the Locust, the Yellow-wood, or more strikingly in the Button-wood or Plane-tree (Fig. [74]).

Fig. 74. An axillary bud, concealed under the hollowed base of the leaf-stalk, in Buttonwood or Plane-tree.

50. The leaf-scars, so conspicuous in Fig. [72, 73], under each axillary bud, mark the place where the stalk of the subtending leaf was attached until it fell in autumn.

[51.] Scaly Buds, which are well represented in Fig. [72, 73], commonly belong to trees and shrubs of countries in which growth is suspended during winter. The scaly coverings protect the tender young parts beneath, not so much by keeping out the cold, which of course would penetrate the bud in time, as by shielding the interior from the effects of sudden changes. There are all gradations between these and

[52.] Naked Buds, in which these scales are inconspicuous or wanting, as in most herbs, at least above ground, and most tropical trees and shrubs. But nearly related plants of the same climate may differ widely in this respect. Rhododendrons have strong and scaly winter-buds; while in Kalmia they are naked. One species of Viburnum, the Hobble-bush, has completely naked buds, what would be a pair of scales developing into the first leaves in spring; while another (the Snowball) has conspicuous scaly buds.

[53.] Vigor of Vegetation from strong buds. Large and strong buds, like those of the Horse-chestnut, Hickory, and the like, contain several leaves, or pairs of leaves, ready formed, folded and packed away in small compass, just as the seed-leaves of a strong embryo are packed away in the seed: they may even contain all the blossoms of the ensuing season, plainly visible as small buds. And the stems upon which these buds rest are filled with abundant nourishment, which was deposited the summer before in the wood or in the bark. Under the surface of the soil, or on it covered with the fallen leaves of autumn, similar strong buds of our perennial herbs may be found; while beneath are thick roots, rootstocks, or tubers, charged with a great store of nourishment for their use. This explains how it is that vegetation from such buds shoots forth so vigorously in the spring of the year, and clothes the bare and lately frozen surface of the soil, as well as the naked boughs of trees, very promptly with a covering of fresh green, and often with brilliant blossoms. Everything was prepared, and even formed, beforehand: the short joints of stem in the bud have only to lengthen, and to separate the leaves from each other so that they may unfold and grow. Only a small part of the vegetation of the season comes directly from the seed, and none of the earliest vernal vegetation. This is all from buds which have lived through the winter.

[54.] The Arrangement of Branches, being that of axillary buds, answers to that of the leaves. Now leaves principally are either opposite or alternate. Leaves are opposite when there are two from the same joint of stem, as in Maples (Fig. [20]), the two being on opposite sides of the stem; and so the axillary buds and branches are opposite, as in Fig. [75]. Leaves are alternate when there is only one from each joint of stem, as in the Oak, Lime-tree, Poplar, Button-wood (Fig. [74]), Morning-Glory (Fig. [45],—not counting the seed-leaves, which of course are opposite, there being a pair of them); also in Indian Corn (Fig. [70]), and Iris (Fig. [59]). Consequently the axillary buds are also alternate, as in Hickory (Fig. [73]); and the branches they form alternate,—making a different kind of spray from the other mode, one branch shooting on one side of the stem and the next on some other. For in the alternate arrangement no leaf is on the same side of the stem as the one next above or next below it.

55. But the symmetry of branches (unlike that of the leaves) is rarely complete. This is due to several causes, and most commonly to the

[56.] Non-development of buds. It never happens that all the buds grow. If they did, there might be as many branches in any year as there were leaves the year before. And of those which do begin to grow, a large portion perish, sooner or later, for want of nourishment, or for want of light, or because those which first begin to grow have an advantage, which they are apt to keep, taking to themselves the nourishment of the stem, and starving the weaker buds. In the Horse-chestnut (Fig. [72]), Hickory (Fig. [73]), Magnolia, and most other trees with large scaly buds, the terminal bud is the strongest, and has the advantage in growth; and next in strength are the upper axillary buds: while the former continues the shoot of the last year, some of the latter give rise to branches, and the rest fail to grow. In the Lilac also (Fig. [75]), the uppermost axillary buds are stronger than the lower; but the terminal bud rarely appears at all; in its place the uppermost pair of axillary buds grow, and so each stem branches every year into two,—making a repeatedly two-forked ramification, as in Fig. [76].

Fig. 75. Shoot of Lilac, with winter buds; the two uppermost axillary ones strong; the terminal not developed. 76. Forking ramification of Lilac; reduced in size.

[57.] Latent Buds. Axillary buds that do not grow at the proper season, and especially those which make no appearance externally, may long remain latent, and at length upon a favorable occasion start into growth, so forming branches apparently out of place as they are out of time. The new shoots seen springing directly out of large stems may sometimes originate from such latent buds, which have preserved their life for years. But commonly these arise from

[58.] Adventitious Buds. These are buds which certain shrubs and trees produce anywhere on the surface of the wood, especially where it has been injured. They give rise to the slender twigs which often feather the sides of great branches of our American Elms. They sometimes form on the root, which naturally is destitute of buds; they are even found upon some leaves; and they are sure to appear on the trunks and roots of Willows, Poplars, and Chestnuts, when these are wounded or mutilated. Indeed Osier-Willows are pollarded, or cut off, from time to time, by the cultivator, for the purpose of producing a crop of slender adventitious twigs, suitable for basket-work. Such branches, being altogether irregular, of course interfere with the natural symmetry of the tree. Another cause of irregularity, in certain trees and shrubs, is the formation of what are called

Fig. 77. Tartarean Honeysuckle, with three accessory buds in each axil.

[59.] Accessory or Supernumerary Buds. There are cases where two, three, or more buds spring from the axil of a leaf, instead of the single one which is ordinarily found there. Sometimes they are placed one over the other, as in the Aristolochia or Pipe-Vine, and in the Tartarean Honeysuckle (Fig. [77]); also in the Honey-Locust, and in the Walnut and Butternut (Fig. [78]), where the upper supernumerary bud is a good way out of the axil and above the others. And this is here stronger than the others, and grows into a branch which is considerably out of the axil, while the lower and smaller ones commonly do not grow at all. In other cases three buds stand side by side in the axil, as in the Hawthorn, and the Red Maple (Fig. [79].) If these were all to grow into branches, they would stifle each other. But some of them are commonly flower-buds: in the Red Maple, only the middle one is a leaf-bud, and it does not grow until after those on each side of it have expanded the blossoms they contain.

Fig. 78. Butternut branch, with accessory buds, the uppermost above the axil.

Fig. 79. Red-Maple branch, with accessory buds placed side by side. The annular lines toward the base in this and in Fig. [72] are scars of the bud-scales, and indicate the place of the winter-bud of the preceding year.

[60.] Sorts of Buds. It may be useful to enumerate the kinds of buds which have been described or mentioned. They are

Terminal, when they occupy the summit of (or terminate) a stem,

Lateral, when they are borne on the side of a stem; of which the regular kind is the

Axillary, situated in the axil of a leaf. These are

Accessory or Supernumerary, when they are in addition to the normal solitary bud; and these are Collateral, when side by side; Superposed, when one above another;

Extra-axillary, when they appear above the axil, as some do when superposed, and as occasionally is the case when single.

Naked buds; those which have no protecting scales.

Scaly buds; those which have protecting scales, which are altered leaves or bases of leaves.

Leaf-buds, contain or give rise to leaves, and develop into a leafy shoot.

Flower-buds, contain or consist of blossoms, and no leaves.

Mixed buds, contain both leaves and blossoms.

[61.] Definite annual Growth from winter buds is marked in most of the shoots from strong buds, such as those of the Horse-chestnut and Hickory (Fig. [72, 73]). Such a bud generally contains, already formed in miniature, all or a great part of the leaves and joints of stem it is to produce, makes its whole growth in length in the course of a few weeks, or sometimes even in a few days, and then forms and ripens its buds for the next year's similar growth.

[62.] Indefinite annual Growth, on the other hand, is well marked in such trees or shrubs as the Honey-Locust, Sumac, and in sterile shoots of the Rose, Blackberry, and Raspberry. That is, these shoots are apt to grow all summer long, until stopped by the frosts of autumn or some other cause. Consequently they form and ripen no terminal bud protected by scales, and the upper axillary buds are produced so late in the season that they have no time to mature, nor has their wood time to solidify and ripen. Such stems therefore commonly die back from the top in winter, or at least all their upper buds are small and feeble; so the growth of the succeeding year takes place mainly from the lower axillary buds, which are more mature.

[63.] Deliquescent and Excurrent Growth. In the former case, and wherever axillary buds take the lead, there is, of course, no single main stem, continued year after year in a direct line, but the trunk is soon lost in the branches. Trees so formed commonly have rounded or spreading tops. Of such trees with deliquescent stems,—that is, with the trunk dissolved, as it were, into the successively divided branches,—the common American Elm (Fig. [80]) is a good illustration.

Fig. 80. An American Elm, with Spruce-trees, and on the left Arbor Vitæ.

64. On the other hand, the main stem of Firs and Spruces, unless destroyed by some injury, is carried on in a direct line throughout the whole growth of the tree, by the development year after year of a terminal bud: this forms a single, uninterrupted shaft,—an excurrent trunk, which cannot be confounded with the branches that proceed from it. Of such spiry or spire-shaped trees, the Firs or Spruces are characteristic and familiar examples. There are all gradations between the two modes.

Section V. ROOTS.

65. It is a property of stems to produce roots. Stems do not spring from roots in ordinary cases, as is generally thought, but roots from stems. When perennial herbs arise from the ground, as they do at spring-time, they rise from subterranean stems.

[66.] The Primary Root is a downward growth from the root-end of the caulicle, that is, of the initial stem of the embryo (Fig. [5-7], [81]). If it goes on to grow it makes a main or tap-root, as in Fig. [37], etc. Some plants keep this main root throughout their whole life, and send off only small side branches; as in the Carrot and Radish: and in various trees, like the Oak, it takes the lead of the side-branches for several years, unless accidentally injured, as a strong tap-root. But commonly the main root divides off very soon, and is lost in the branches. Multiple primary roots now and then occur, as in the seedling of Pumpkin (Fig. [27]), where a cluster is formed even at the first, from the root-end of the caulicle.

Fig. 81. Seedling Maple, of the natural size; the root well supplied with root hairs, here large enough to be seen by the naked eye. 82. Lower end of this root, magnified, the root seen just as root-hairs are beginning to form a little behind the tip.

[67.] Secondary Roots are those which arise from other parts of the stem. Any part of the stem may produce them, but they most readily come from the nodes. As a general rule they naturally spring, or may be made to spring, from almost any young stem, when placed in favorable circumstances,—that is, when placed in the soil, or otherwise supplied with moisture and screened from the light. For the special tendency of the root is to avoid the light, seek moisture, and therefore to bury itself in the soil. Propagation by division, which is so common and so very important in cultivation, depends upon the proclivity of stems to strike root. Stems or branches which remain under ground give out roots as freely as roots themselves give off branches. Stems which creep on the ground most commonly root at the joints; so will most branches when bent to the ground, as in propagation by layering; and propagation by cuttings equally depends upon the tendency of the cut end of a shoot to produce roots. Thus, a piece of a plant which has stem and leaves, either developed or in the bud, may be made to produce roots, and so become an independent plant.

[68.] Contrast between Stem and Root. Stems are ascending axes; roots are descending axes. Stems grow by the successive development of internodes ([13]), one after another, each leaf-bearing at its summit (or node); so that it is of the essential nature of a stem to bear leaves. Roots bear no leaves, are not distinguishable into nodes and internodes, but grow on continuously from the lower end. They commonly branch freely, but not from any fixed points nor in definite order.

69. Although roots generally do not give rise to stems, and therefore do not propagate the plant, exceptions are not uncommon. For as stems may produce adventitious buds, so also may roots. The roots of the Sweet Potato among herbs, and of the Osage Orange among trees freely produce adventitious buds, developing into leafy shoots; and so these plants are propagated by root-cuttings. But most growths of subterranean origin which pass for roots are forms of stems, the common Potato for example.

70. Roots of ordinary kinds and uses may be roughly classed into fibrous and fleshy.

[71.] Fibrous Roots, such as those of Indian Corn (Fig. [70]), of most annuals, and of many perennials, serve only for absorption: these are slender or thread-like. Fine roots of this kind, and the fine branches which most roots send out are called Rootlets.

[72.] The whole surface of a root absorbs moisture from the soil while fresh and new; and the newer roots and rootlets are, the more freely do they imbibe. Accordingly, as long as the plant grows above ground, and expands fresh foliage, from which moisture largely escapes into the air, so long it continues to extend and multiply its roots in the soil beneath, renewing and increasing the fresh surface for absorbing moisture, in proportion to the demand from above. And when growth ceases above ground, and the leaves die and fall, or no longer act, then the roots generally stop growing, and their soft and tender tips harden. From this period, therefore, until growth begins anew the next spring, is the best time for transplanting; especially for trees and shrubs.

73. The absorbing surface of young roots is much increased by the formation, near their tips, of Root-hairs (Fig. [81, 82]), which are delicate tubular outgrowths from the surface, through the delicate walls of which moisture is promptly imbibed.

Fig. 83-85. Forms of tap-root.

[74.] Fleshy Roots are those in which the root becomes a storehouse of nourishment. Typical roots of this kind are those of such biennials as the turnip and carrot; in which the food created in the first season's vegetation is accumulated, to be expended the next season in a vigorous growth and a rapid development of flowers, fruit, and seed. By the time the seed is matured the exhausted root dies, and with it the whole plant.

75. Fleshy roots may be single or multiple. The single root of the commoner biennials is the primary root, or tap-root, which begins to thicken in the seedling. Names are given to its shapes, such as

Conical, when it thickens most at the crown, or where it joins the stem, and tapers regularly downwards to a point, as in the Parsnip and Carrot (Fig. [84]);

Turnip-shaped or napiform, when greatly thickened above, but abruptly becoming slender below; as the Turnip (Fig. [83]); and

Spindle-shaped, or Fusiform, when thickest in the middle and tapering to both ends; as the common Radish (Fig. [85]).

76. These examples are of primary roots. It will be seen that turnips, carrots, and the like, are not pure root throughout; for the caulicle, from the lower end of which the root grew, partakes of the thickening, perhaps also some joints of stem above: so the bud-bearing and growing top is stem.

Fig. 86. Sweet-Potato plant forming thickened roots. Some in the middle are just beginning to thicken; one at the left has grown more; one at the right is still larger.

Fig. 87. Fascicled fusiform roots of a Dahlia: a, a, buds on base of stem.

77. A fine example of secondary roots ([67]), some of which remain fibrous for absorption, while a few thicken and store up food for the next season's growth, is furnished by the Sweet Potato (Fig. [86]). As stated above, these are used for propagation by cuttings; for any part will produce adventitious buds and shoots. The Dahlia produces fascicled (i. e. clustered) fusiform roots of the same kind, at the base of the stem (Fig. [87]): but these, like most roots, do not produce adventitious buds. The buds by which Dahlias are propagated belong to the surviving base of the stem above.

[78.] Anomalous Roots, as they may be called, are those which subserve other uses than absorption, food-storing, and fixing the plant to the soil.

Aerial Roots, i. e. those that strike from stems in the open air, are common in moist and warm climates, as in the Mangrove which reaches the coast of Florida, the Banyan, and, less strikingly, in some herbaceous plants, such as Sugar Cane, and even in Indian Corn. Such roots reach the ground at length, or tend to do so.

Aerial Rootlets are abundantly produced by many climbing plants, such as the Ivy, Poison Ivy, Trumpet Creeper, etc., springing from the side of stems, which they fasten to trunks of trees, walls, or other supports. These are used by the plant for climbing.

Fig. 88. Epiphytes of Florida and Georgia, viz., Epidendrum conopseum, a small Orchid, and Tillandsia usneoides, the so-called Long Moss or Black Moss, which is no moss, but a flowering plant, also T. recurvata; on a bough of Live Oak.

[79.] Epiphytes, or Air-Plants (Fig. [88]), are called by the former name because commonly growing upon the trunks or limbs of other plants; by the latter because, having no connection with the soil, they must derive their sustenance from the air only. They have aerial roots, which do not reach the ground, but are used to fix the plant to the surface upon which the plant grows: they also take a part in absorbing moisture from the air.

[80.] Parasitic Plants, of which there are various kinds, strike their roots, or what answer to roots, into the tissue of foster plants, or form attachments with their surface, so as to prey upon their juices. Of this sort is the Mistletoe, the seed of which germinates on the bough where it falls or is left by birds; and the forming root penetrates the bark and engrafts itself into the wood, to which it becomes united as firmly as a natural branch to its parent stem; and indeed the parasite lives just as if it were a branch of the tree it grows and feeds on. A most common parasitic herb is the Dodder; which abounds in low grounds in summer, and coils its long and slender, leafless, yellowish stems—resembling tangled threads of yarn—round and round the stalks of other plants; wherever they touch piercing the bark with minute and very short rootlets in the form of suckers, which draw out the nourishing juices of the plants laid hold of. Other parasitic plants, like the Beech-drops and Pine-sap, fasten their roots under ground upon the roots of neighboring plants, and rob them of their juices.

81. Some plants are partly parasitic; while most of their roots act in the ordinary way, others make suckers at their tips which grow fast to the roots of other plants and rob them of nourishment. Some of our species of Gerardia do this (Fig. [89]).

Fig. 89. Roots of Yellow Gerardia, some attached to and feeding on the root of a Blueberry-bush.

82. There are phanerogamous plants, like Monotropa or Indian Pipe, the roots of which feed mainly on decaying vegetable matter in the soil. These are Saprophytes, and they imitate Mushrooms and other Fungi in their mode of life.

[83.] Duration of Roots, etc. Roots are said to be either annual, biennial, or perennial. As respects the first and second, these terms may be applied either to the root or to the plant.

[84.] Annuals, as the name denotes, live for only one year, generally for only a part of the year. They are of course herbs; they spring from the seed, blossom, mature their fruit and seed, and then die, root and all. Annuals of our temperate climates with severe winters start from the seed in spring, and perish at or before autumn. Where the winter is a moist and growing season and the summer is dry, winter annuals prevail; their seeds germinate under autumn or winter rains, grow more or less during winter, blossom, fructify, and perish in the following spring or summer. Annuals are fibrous-rooted.

[85.] Biennials, of which the Turnip, Beet, and Carrot are familiar examples, grow the first season without blossoming, usually thicken their roots, laying up in them a stock of nourishment, are quiescent during the winter, but shoot vigorously, blossom, and seed the next spring or summer, mainly at the expense of the food stored up, and then die completely. Annuals and biennials flower only once; hence they have been called Monocarpic (that is, once-fruiting) plants.

[86.] Perennials live and blossom year after year. A perennial herb, in a temperate or cooler climate, usually dies down to the ground at the end of the season's growth. But subterranean portions of stem, charged with buds, survive to renew the development. Shrubs and trees are of course perennial; even the stems and branches above ground live on and grow year after year.

87. There are all gradations between annuals and biennials, and between these and perennials, as also between herbs and shrubs; and the distinction between shrubs and trees is quite arbitrary. There are perennial herbs and even shrubs of warm climates which are annuals when raised in a climate which has a winter,—being destroyed by frost. The Castor-oil plant is an example. There are perennial herbs of which only small portions survive, as off-shoots, or, in the Potato, as tubers, etc.

Section VI. STEMS.

[88.] The Stem is the axis of the plant, the part which bears all the other organs. Branches are secondary stems, that is, stems growing out of stems. The stem at the very beginning produces roots, in most plants a single root from the base of the embryo-stem, or caulicle. As this root becomes a descending axis, so the stem, which grows in the opposite direction is called the ascending axis. Rising out of the soil, the stem bears leaves; and leaf-bearing is the particular characteristic of the stem. But there are forms of stems that remain underground, or make a part of their growth there. These do not bear leaves, in the common sense; yet they bear rudiments of leaves, or what answers to leaves, although not in the form of foliage. The so-called stemless or acaulescent plants are those which bear no obvious stem (caulis) above ground, but only flower-stalks, and the like.

[89.] Stems above ground, through differences in duration, texture, and size, form herbs, shrubs, trees, etc., or in other terms are

Herbaceous, dying down to the ground every year, or after blossoming.

Suffrutescent, slightly woody below, there surviving from year to year.

Suffruticose or Frutescent, when low stems are decidedly woody below, but herbaceous above.

Fruticose or Shrubby, woody, living from year to year, and of considerable size,—not, however, more than three or four times the height of a man.

Arborescent, when tree-like in appearance or mode of growth, or approaching a tree in size.

Arboreous, when forming a proper tree-trunk.

90. As to direction taken in growing, stems may, instead of growing upright or erect, be

Diffuse, that is, loosely spreading in all directions.

Declined, when turned or bending over to one side.

Decumbent, reclining on the ground, as if too weak to stand.

Assurgent or Ascending, rising obliquely upwards.

Procumbent or Prostrate, lying flat on the ground from the first.

Creeping or Repent, prostrate on or just beneath the ground, and striking root, as does the White Clover, the Partridge-berry, etc.

Climbing or Scandent, ascending by clinging to other objects for support, whether by tendrils, as do the Pea, Grape-Vine, and Passion-flower and Virginia Creeper (Fig. [92], [93]); by their twisting leaf-stalks, as the Virgin's Bower; or by rootlets, like the Ivy, Poison Ivy, and Trumpet Creeper.

Twining or Voluble, when coiling spirally around other stems or supports; like the Morning-Glory (Fig. [90]) and the Hop.

Fig. 90. Twining or voluble stem of Morning-Glory.

91. Certain kinds of stems or branches, appropriated to special uses, have received distinct substantive names; such as the following:

[92.] A Culm, or straw-stem, such as that of Grasses and Sedges.

[93.] A Caudex is the old name for such a peculiar trunk as a Palm-stem; it is also used for an upright and thick rootstock.

[94.] A Sucker is a branch rising from stems under ground. Such are produced abundantly by the Rose, Raspberry, and other plants said to multiply "by the root." If we uncover them, we see at once the great difference between these subterranean branches and real roots. They are only creeping branches under ground. Remarking how the upright shoots from these branches become separate plants, simply by the dying off of the connecting under-ground stems, the gardener expedites the result by cutting them through with his spade. That is, he propagates the plant "by division."

[95.] A Stolon is a branch from above ground, which reclines or becomes prostrate and strikes root (usually from the nodes) wherever it rests on the soil. Thence it may send up a vigorous shoot, which has roots of its own, and becomes an independent plant when the connecting part dies, as it does after a while. The Currant and the Gooseberry naturally multiply in this way, as well as by suckers (which are the same thing, only the connecting part is concealed under ground). Stolons must have suggested the operation of layering by bending down and covering with soil branches which do not naturally make stolons; and after they have taken root, as they almost always will, the gardener cuts through the connecting stem, and so converts a rooting branch into a separate plant.

[96.] An Offset is a short stolon, or sucker, with a crown of leaves at the end, as in the Houseleek (Fig. [91]), which propagates abundantly in this way.

Fig. 91. Houseleek (Sempervivum), with offsets.

[97.] A Runner, of which the Strawberry presents the most familiar and characteristic example, is a long and slender, tendril-like stolon, or branch from next the ground, destitute of conspicuous leaves. Each runner of the Strawberry, after having grown to its full length, strikes root from the tip, which fixes it to the ground, then forms a bud there, which develops into a tuft of leaves, and so gives rise to a new plant, which sends out new runners to act in the same way. In this manner a single Strawberry plant will spread over a large space, or produce a great number of plants, in the course of the summer, all connected at first by the slender runners; but these die in the following winter, if not before, and leave the plants as so many separate individuals.

[98.] Tendrils are branches of a very slender sort, like runners, not destined like them for propagation, and therefore always destitute of buds or leaves, being intended only for climbing. Simple tendrils are such as those of Passion-flowers (Fig. [92]). Compound or branching tendrils are borne by the Cucumber and Pumpkin, by the Grape-Vine, Virginia Creeper, etc.

Fig. 92. A small Passion-flower (Passiflora sicyoides), showing the tendrils.

99. A tendril commonly grows straight and outstretched until it reaches some neighboring support, such as a stem, when its apex hooks around it to secure a hold; then the whole tendril shortens itself by coiling up spirally, and so draws the shoot of the growing plant nearer to the supporting object. But the tendrils of the Virginia Creeper (Ampelopsis, Fig. [93]), as also the shorter ones of the Japanese species, effect the object differently, namely, by expanding the tips of the tendrils into a flat disk, with an adhesive face. This is applied to the supporting object, and it adheres firmly; then a shortening of the tendril and its branches by coiling brings up the growing shoot close to the support. This is an adaptation for climbing mural rocks or walls, or the trunks of trees, to which ordinary tendrils are unable to cling. The Ivy and Poison Ivy attain the same result by means of aerial rootlets ([78]).

Fig. 93. Piece of the stem of Virginia Creeper, bearing a leaf and a tendril. 94. Tips of a tendril, about the natural size, showing the disks by which they hold fast to walls, etc.

100. Some tendrils are leaves or parts of leaves, as those of the Pea (Fig. [35]). The nature of the tendril is known by its position. A tendril from the axil of a leaf, like that of Passion-flowers (Fig. [92]) is of course a stem, i. e. a branch. So is one which terminates a stem, as in the Grape-Vine.

[101.] Spines or Thorns (Fig. [95, 96]) are commonly stunted and hardened branches or tips of stems or branches, as are those of Hawthorn, Honey-Locust, etc. In the Pear and Sloe all gradations occur between spines and spine-like (spinescent) branches. Spines may be reduced and indurated leaves; as in the Barberry, where their nature is revealed by their situation, underneath an axillary bud. But prickles, such as those of Blackberry and Roses, are only excrescences of the bark, and not branches.

Fig. 95. A branching thorn of Honey-Locust, being an indurated leafless branch developed from an accessory bud far above the axil: at the cut portion below, three other buds (a) are concealed under the petiole.

Fig. 96. Spine of Cockspur Thorn, developed from an axillary bud, as the leaf-scar below witnesses: an accessory leaf-bud is seen at its base.

102. Equally strange forms of stems are characteristic of the Cactus family (Fig. [111]). These may be better understood by comparison with

[103.] Subterranean Stems and Branches. These are very numerous and various; but they are commonly overlooked, or else are confounded with roots. From their situation they are out of ordinary sight; but they will well repay examination. For the vegetation that is carried on under ground is hardly less varied or important than that above ground. All their forms may be referred to four principal kinds: namely, the Rhizoma (Rhizome) or Rootstock, the Tuber, the Corm or solid bulb, and the true Bulb.