Order XXXIX. CUPULÌFERÆ. (Oak Family.)
This order contains more species of trees and shrubs in temperate regions than any other, except the Coniferæ. The genus Quercus (Oak) alone contains about 20 species of trees in the region covered by this work.
Genus 83. BÉTULA.
Trees or shrubs with simple, alternate, mostly straight-veined, thin, usually serrate leaves. Flowers in catkins, opening in early spring, in most cases before the leaves. Fruit a leafy-scaled catkin or cone, hanging on till autumn. Twigs usually slender, the bark peeling off in thin, tough layers, and having peculiar horizontal marks. Many species have aromatic leaves and twigs.
| * Trunks with chalky white bark. (A.) | |||
| A. Native. (B.) | |||
| B. Small tree with leafstalks about ½ as long as the blades | 1. | ||
| B. Large tree; leafstalks about 1/3 as long as the blades | 2. | ||
| A. Cultivated; from Europe; many varieties | 3. | ||
| * Bark not chalky white, usually dark. (C.) | |||
| C. Leaves and bark very aromatic. (D.) | |||
| D. Bark of trunk yellowish and splitting into filmy layers | 5. | ||
| D. Bark not splitting into filmy layers | 4. | ||
| C. Leaves not very aromatic; bark brownish and loose and shaggy on the main trunk; growing in or near the water | 6. | ||
B. populifòlia.
1. Bétula populifòlia, Ait. (American White or Gray Birch.) Leaves triangular, very taper-pointed, and usually truncate or nearly so at the broad base, irregularly twice-serrate; both sides smooth and shining, when young glutinous with resinous glands; leafstalks half as long as the blades and slender, so as to make the leaves tremulous, like those of the Aspen. Fruit brown, cylindrical, more or less pendulous on slender peduncles. A small (15 to 30 ft. high), slender tree with an ascending rather than an erect trunk. Bark chalky or grayish white, with triangular dusky spaces below the branches; recent shoots brown, closely covered with round dots.
B. papyrífera.