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].