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]).
