B. nìgra.
6. Bétula nìgra, L. (River or Red Birch.) Leaves 2½ to 3½ in. long, rhombic-ovate, acute at both ends, distinctly doubly serrate, bright green above; glaucous beneath when young; on petioles only 1/6 their length. Twigs brown to cinnamon-color, and downy when young. A medium-sized tree, 30 to 50 ft. high, usually growing on the edges of streams, the old trunks having a very shaggy, loose, torn, reddish-brown bark. Wild in Massachusetts, south and west; often cultivated.
Genus 84. ÁLNUS.
Shrubs or small trees with deciduous, alternate, simple, straight-veined leaves with large stipules that remain most of the season. Flowers in catkins. Fruit a small, scaly, open, woody cone, remaining on the plant throughout the year.
| * Native species; growing in wet places. (A.) | |||
| A. Leaves rounded at base; whitened beneath; found north of 41° N. Lat | 1. | ||
| A. Leaves acute or tapering at base; southward. (B.) | |||
| B. Flowering in the spring | 2. | ||
| B. Flowering in the autumn | 3. | ||
| * Cultivated species; from Europe; will grow in dry places | 4, 5. | ||
A. incàna.
1. Álnus incàna, Willd. (Speckled or Hoary Alder.) Leaves 3 to 5 in. long, broadly oval or ovate, rounded at base, sharply serrate, often coarsely toothed, whitened and mostly downy beneath; stipules lanceolate and soon falling. Fruit orbicular or nearly so. A shrub or small tree, 8 to 20 ft. high, with the bark of the trunk a polished reddish green; common along water-courses north of 41° N. Lat.; sometimes cultivated.
