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.