Complete Text (Part 5)

of leaves. 41. The herb and the tree grow in the same way. The difference is only in size and duration. An Herb dies altogether, or dies down to the ground, after it has ripened its fruit, or at the approach of winter. LESSON 4.] GROWTH OF PLANTS FROM BUDS. 21 An annual herb flowers in the first year, and dies, root and all, after ripening its seed: Mustard, Peppergrass, Buckwheat, &«., are examples. A biennial herb — such as the Turnip, Carrot, Beet, and Cabbage —grows the first season without blossoming, survives the winter, flowers after that, and dies, root and all, when it has ripened its seed. A perennial herb lives and blossoms year after year, but dies down to the ground, or near it, annually, — not, however, quite down to the root: for a portion of the stem, with its buds, still survives; and from these buds the shoots of the following year arise. A Shrub is a perennial plant, with woody stems which continue alive and grow year afier year. A. Tree differs from a shrub only in its greater size. 42. The Terminal Bud, There are herbs, shrubs, and trees which do not branch, as we have already seen (35); but whose stems, even when they live for many years, rise as a simple shaft (Fig. 47). These plants grow by the continued evolution of a bud which crowns the summit of the stem, and which is therefore called the terminal bud. This bud is very conspicuous in many branching plants also; as on all the stems or shoots of Maples (Fig. 53), Horsechestnuts (Fig. 48), or Hickories (Fig. 49), of a year old. When they grow, they merely prolong the shoot or stem on which they rest. On these same shoots, however, other buds are to be seen, regularly arranged down their sides. We find them situated just over broad, flattened places, which are the scars left by the fall of the leaf-stalk the autumn previous. Before the fall of the leaf, they would have been seen to occupy their axils (39) : so they are named 43. Axillary Buds, They were formed in these trees early in the summer. Occasionally they grow at the time into branches: at least, some of them are pretty sure to do so, in case the growing terminal bud at the end of the shoot is injured or destroyed. Otherwise they lie dormant until the spring. In many trees or shrubs (such for example as the Sumach and Honey-Locust) these axillary buds do not show themselves until spring; but if FIG. 43, Shoot of Horsechestnut, of one year’s growth, taken in autumn after the leaves have fallon. 22 GROWTH OF PLANTS FROM BUDS. [Lesson 4. searched for, they may be detected, though of small size, hidden under the bark. Sometimes, although early formed, they are con- cealed all summer long under the base of the leaf- stalk, 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. 50). 44, Such large and conspicuous buds as those of the Horsechestnut, Hickory, and the like, are scaly ; the scales being a kind of imperfect leaves. The use of the bud-scales is obvious ; namely, to protect the tender young parts beneath. ‘To do this more effectually, they are often coated on the outside with a varnish which is impervious to wet, while within they, or the parts they enclose, are thickly clothed with down or wool; not really to keep out the cold of winter, which will of course penetrate the bud in time, but to shield the interior against sudden changes from warm to cold, or from cold to warm, which are equally injurious. Scaly buds commonly belong, as would be expect ed, to trees and shrubs of northern climates; while naked buds are usual in tropical regions, as well as in herbs everywhere which branch during the summer's growth and do not endure the winter. 45. But naked buds, or nearly naked, also occur in several of our own trees and shrubs; sometimes pretty large ones, as those of Hob FIG. 49, Annual shoot of the Shagbark Hickory. FIG. 50. Bud and leaf of the Buttonwood, or American Plane-tree. LESSON 4.] GROWTH OF PLANTS FROM BUDS. 23 blebush (while those of the nearly-related Snowball or High Bush- Cranberry are scaly) ; but more commonly, when naked buds occur in trees and shrubs of our climate, they are small, and sunk in the bark, as in the Sumac; or even partly buried in the wood until they begin to grow, as in the Honey-Locust. 46. Vigor of Vegetation from Buds, Large and strong buds, like those of the Horsechestnut, Hickory, and the like, on inspection will be found to contain several leaves, or pairs of leaves, ready formed, folded and packed away in small compass, just as the seed-leaves are packed away in the seed: they 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, we may find similar strong buds of our perennial herbs, in great variety ; while beneath are thick roots, rootstocks, or tubers, charged with a great store of nourishment for their use. As we regard these, we shall readily perceive how it is that vegetation 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, almost at once with a covering of the freshest 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 vege- tation 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. 47. This growth from buds, in manifold variety, is as interesting a subject of study as the growth of the plantlet from the seed, and is still easier to observe. We have only room here to sketch the general plan; earnestly recommending tho student to examine at- tentively their mode of growth in all the common trees and shrubs, when they shoot forth in spring. The growth of the terminal bud prolongs the stem or branch: the growth of axillary buds pro- duces branches. 48. The Arrangement of Branches is accordingly the same as of axillary buds; and the arrangement of these buds is the same as that of the leaves. Now leaves are arranged in two principal ways: they are either opposite or alternate. Leaves are vpposite when 24 GROWTH OF PLANTS FROM BUDS. [wzsson 4. there are two borne on the same joint of stem, as in the Horse- chestnut, Maple (Fig. 7), Honeysuckle (Fig. 132), Lilac, &e.; the two leaves in such cases being always opposite each other, that is, on exactly opposite sides of the stem. Here of course the buds in their axils are opposite, as we observe in Fig. 48, where the leaves have fallen, but their place is shown by the scars. And the branches into which the buds grow are likewise opposite each other in pairs. 49, Leaves are alternate when there is only one from each joint of stem, as in the Oak (Fig. 22), Lime-tree, Poplar, Buttonwood (Fig. 50), Morning-Glory (Fig. 8),— not counting the seed-leaves, which of course are opposite, there being a pair of them; also in Indian Corn (Fig. 42), and Iris (Fig. 44). Consequently the axillary buds are also alternate, as in Hickory (Fig. 49); and the branches they form alternate, — making a different kind of spray from the other mode, —one branch shooting on the 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. 50. Branches, therefore, are arranged with symmetry ; and the mode of branching of the whole tree may be foretold by a glance at the arrangement of the leaves on the seedling or stem of the first year. This arrangement of the branches according to that of the leaves is always plainly to be recognized; but the symmetry of branches is rarely complete. This is owing to several causes ; mainly to one, viz: — 51. It never happens that all the bud: grow. If they did, there would 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. 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. 52. In the Horsechestnut (Fig. 48), Hickory (Fig. 49), Mag- nolia, 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, while the rest fail to grow. In the Lilac also, the upper axillary buds are stronger than the lower; but the terminal bud rarely LESsoN 4.] GROWTH OF PLANTS FROM BUDS. 25 appears at all; in its place the uppermost pair of axillary buds grow, and so each stem branches every year into two; making a re- peatedly two-forked ramification. 53. In these and many similar trees and shrubs, most of the shoots make a definite annual growth. That is, each shoot of the season develops rapidly from a strong bud in spring, —a bud which gen- erally 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 rapid growth. 54. On the other hand, the Locust, Honey-Locust, Sumac, and, among smaller plants, the Rose and Raspberry, make an indefinite annual growth. That is, their stems grow on all summer long, until stopped by the frosts of autumn or some other cause; con- sequently 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 the wood time to solidify and ripen. Such stems therefore commonly die at the top in winter, or at least all their upper buds are small and feeble ; and the growth of the succeeding year takes place mainly from the lower axillary buds, which are more mature. Most of our perennial herbs grow in this way, their stems dying down to the ground every year: the part beneath, however, is charged with vigorous buds, well pro- tected by the kindly covering of earth, ready for the next year’s vegetation. 55. In these last-mentioned cases 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 ; and when they grow into trees, these 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. 54) furnishes a good illustration. 56. On the other hand, the main stem of Pines and Spruces, as it begins in the seedling, 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 can never be con- founded with the branches that proceed from it. Of such spiry or spire-shaped trees, the Firs or Spruces are the most perfect and 3 26 GROWTH OF PLANTS FROM BUDS. [wesson 4. familiar illustrations (Fig. 54); but some other trees with strong terminal buds exhibit the same character for a certain time, and in a less marked degree. 57. Latent Buds, Some of the axillary buds grow the following year into branches; but a larger number do not (51). These do not necessarily die. Qften they survive in a latent state for some years, visible on the surface of the branch, or are smaller and concealed under the bark, resting on the sarface of the wood: and when at any time the other buds or branches happen to be killed, these older latent buds grow to supply their place ;— as is often seen when the foliage and young shoots of a tree are destroyed by insects. 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 so beautifully the sides of great branches or trunks of our American Elms. They sometimes form on the root, which naturally is destitute of buds ; 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 sym- metry of the tree (50). Another cause of irregularity, in certain trees and shrubs, is the formation of what are called 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 Tartarian Honeysuckle (Fig. 51) ; also in the 3 Honey-Locust, and in the Walnut and Butternut (Fig. 52), where the upper supernumerary bud is a good way out of the axil and above the others. And this is here stronger fi FIG. 51. Tartarian Honeysuckle, with three accessory buds in one axil. LESSON 4.] GROWTH OF PLANTS FROM BUDS. 27 than the others, and grows into a branch which is considerably out ot the axil, while the lower and smaller ones commonly do not grow at all. In other cases the three buds stand side by side in the axil, as in the Hawthorn, and the Red Maple (Fig. 53). If these were all to grow into branches, they would stifle or jostle 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 ex- panded the blossoms they contain. 60. Sorts of Buds, It may be useful to enumerate the kinds of buds which have now been mentioned, referring back to the paragraphs in which the pe- culiarities of each are explained. Buds, then, are either terminal or lateral. They are Terminal when they rest on the apex of a stem (42). The earliest terminal bud is the plumule of the embryo (16). Lateral, when they appear on the side of a stem:—of which the only regular kind is the Azillary (43), namely, those which are situated in the axils of leaves. Accessory or Supernumerary (59), when two or more occur in addition to the ordinary axillary bud. Adventitious (58), when they occur out of the axils and without order, on stems or roots, or even on leaves. Any of these kinds may be, either Naked, when without coverings; or scaly, when protected by seales (44, 45). Latent, when they survive long without growing, and commonly without being visible externally (57). Leaf-buds, when they contain leaves, and develop into a leafy shoot. Flower-buds, when they contain blossoms, and no leaves, as the FIG. 52, Butternut branch, with accessory buds, the uppermost above the axil. FIG, 52, Red-Maple branch, with accessory buds placed side by side. 28 MORPHOLOGY OF ROOTS. [Lesson 5. side-buds of the Red-Maple, or when they are undeveloped blossoms, These we shall have to consider hereafter. Figure 54 represents a spreading-topped tree (American Elm), the stem dividing off into branches ; and some spiry trees (Spruces on the right hand, and two of the Arbor-Vite on the left) with ex- current stems. LESSON V. MORPHOLOGY (i.€. VARIOUS SORTS AND FORMS) OF ROOTS. 61. Morphology. as the name (derived from two Greek words) denotes, is the doctrine of forms. In treating of forms in plants, the botanist is not confined to an enumeration or description of the shapes or sorts that occur, — which would be a dull and tedious business. — but he endeavors to bring to view the relations between one form and another ; and this is an interesting study. 62. Botanists give particular names to all the parts of plants, and ako particuiar terms to express their principal varieties in form. They use these terms with great precision and advantage in describ- ing the species or kinds of plants. They must therefore be defined and explained in our