Fig. 14.
Position and Number.—While the axils of the leaves and the ends of the stems are the ordinary places for the buds, there are many peculiarities in regard to their exact position, number, etc., that render them very interesting for winter study. Sometimes there are several to the single leaf. In the Silver Maple there are buds on each side of the true axillary one; these are flower-buds, and during the winter they are larger than the one which produces the branch. The Butternut ([Fig. 14]) and the Walnut have several above each other, the upper one being the largest and at quite a distance from the true axil. In these cases the uppermost is apt to grow, and then the branch is said to be extra-axillary. In the Sycamore the bud does not show while the leaf remains on the tree, as it is in the hollow of the leafstalk. In the winter the bud has a ring-like scar entirely around it, instead of the moon-shaped scar below as in most trees. The Common Locust has several buds under the leafstalk and one above it in the axil. This axillary bud may grow during the time the leaf remains on the tree, and afterward the growth of the strongest one of the others may give the tree two branches almost together.
Some plants form extra buds especially when they are bruised or injured; those which have the greatest tendency to do so are the Willows, Poplars, and Elms. Such buds and growths are called adventitious. By cutting off the tops or pollarding such trees, a very great number of adventitious branches can be made to grow. In this way the Willow-twigs used for baskets are formed. Adventitious buds form the clusters of curious thorns on the Honey-locust and the tufts of whip-like branches on the trunks and large limbs of the Elms.
In trees the terminal bud and certain axillary ones, differing according to the species or variety of tree, are, during the winter, much larger than the rest. These are the ones which naturally form the new growth, and upon their arrangement the character of branching and thus the form of the tree depend. Each species has some peculiarity in this regard, and thus there are differences in the branching of all trees. In opposite-leaved plants the terminal bud may be small and weak, while the two buds at its side may be strong and apt to grow. This causes a forking of the branches each year. This plan is not rare among shrubs, the Lilac being a good example.
Bud-Scales.—The coverings of buds are exceedingly varied, and are well worthy of study and investigation. The large terminal buds of the Horse-chestnut, with their numerous scales, gummy on the outside to keep out the dampness, and hairy within to protect them from sudden changes of temperature, represent one extreme of a long line; while the small, naked, and partly buried buds of the Honey-locust or the Sumac represent the other end.
The scales of many buds are merely extra parts formed for their protection, and fall immediately after the bursting of the buds; while other buds have the stipules of the leaves as bud-scales; these remain on the twigs for a time in the Tulip-tree, and drop immediately in the Magnolia.
Forms of Buds.—The size of buds varies greatly, as before stated, but this difference in size is no more marked than the difference in form. There is no better way to recognize a Beech at any time of the year than by its very long, slender, and sharp-pointed buds. The obovate and almost stalked buds of the Alders are also very conspicuous and peculiar. In the Balsam Poplar the buds are large, sharp-pointed, and gummy; in the Ailanthus they cannot be seen.
Fig. 15.