Trees of the Northern United States. A. C. Apgar
Catalpa, Hibiscus.
Fig. 13.
All the dry, scaly fruits, usually formed by the ripening of some sort of catkin of flowers, will be included under the term cone. Pine, Alder, Magnolia. If the appearance of the fruit is not much different from that of the cluster of flowers, as in the Hornbeams, Willows, and Birches, the term catkin will be retained for the fruit also. The scales of a cone may lap over each other; they are then said to be imbricated or overlapping, (Pine); or they may merely touch at their edges, when they are valvate (Cypress). When cones or catkins hang downward, they are pendent. If the scales have projecting points, these points are spines if strong, and prickles if weak. The parts back of the scales are bracts; these often project beyond the scales, when they are said to be exserted. Sometimes the exserted bracts are bent backward; they are then said to be recurved or reflexed.
Chapter V.
Winter Study of Trees.
Many of the peculiarities of trees can be studied much better during the winter and early spring than at any other time of the year. The plan of branching, the position, number, size, form, color, and surface of buds, as well as the arrangement of the leaves within the bud and the peculiarities of the scales that cover them, are points for winter investigation.
General Plan of Branching.—There are two distinct and readily recognized systems of branching. 1. The main stem is excurrent (Fig. 3) when the trunk extends as an undivided stem throughout the tree to the tip; this causes the spire-like or conical trees so common among narrow-leaved evergreens. 2. The main stem is deliquescent (Fig. 4) when the trunk divides into many, more or less equal divisions, forming the broad-topped, spreading trees. This plan is the usual one among deciduous trees. A few species, however, such as the Sweet Gum and the Sugar-maple, show the excurrent stem while young, yet even these have a deliquescent stem later in life. The English Maple and the Apple both have a deliquescent stem very early.
All the narrow-leaved evergreens, and many of the broad-leaved trees as well, show what is called definite annual growths; that is, a certain amount of leaf and stem, packed up in the winter bud, spreads out and hardens with woody tissue early in the year, and then, no matter how long the season remains warm, no additional leaves or stem will grow. The buds for the next year's growth then form and often become quite large before autumn.
There are many examples among the smaller plants, but rarely one among the trees, of indefinite annual growth; that is, the plant puts forth leaves and forms stems throughout the whole growing-season. The common Locust, the Honey-locust, and the Sumacs are illustrations.
Buds.—Buds are either undeveloped branches or undeveloped flowers. They contain within the scales, which usually cover them, closely packed leaves; these leaves are folded and wrinkled in a number of different ways that will be defined at the end of this chapter.
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.
All the things that might be learned from a small winter twig cannot be shown in an engraving, but the figures here given illustrate some of the facts easily determined from such specimens. The first twig (Ash) had opposite leaves and is 3 years old (the end of each year's growth is marked by dotted lines on all the figures); the year before last it had 6 leaves on the middle portion; last year it had 8 leaves on the end portion and 12 on the side shoots of the middle portion. The buds near the end of the annual growth are strongest and are most apt to grow. The specimen illustrated was probably taken from the end of a branch of a rather young and luxuriantly growing tree. Thus the Ash must have quite a regular growth and form a regularly outlined tree.
The second twig (Sweet Gum) shows 7 years' growth and is probably a side shoot from more or less within the tree-top. It is stunted in its growth by the want of light and room. The leaves were alternate.
The third twig (Sycamore) also had alternate leaves; the pointed buds must have been under the leafstalks, as the leaf-scars show as rings around the buds. The larger branch grew three years ago. From the specimen one judges that the Sycamore is quite an irregularly formed tree. The twig had 11 leaves last year.
The fourth twig (Silver Maple) shows that the plant had opposite leaves, and supernumerary buds at the sides of the true axillary ones; the true axillary buds are smaller than those at the sides. It would, in such cases, be reasonable