5. =Betula lutea=, Michx. f. (YELLOW OR GRAY BIRCH.) A species so like
the preceding (Betula lenta) as to be best described by stating the
differences. Leaves and bark are much less aromatic. Leaves 3 to 5 in.
long, not so often nor so plainly heart-shaped at base, usually
narrowed; less bright green above, and more downy beneath; more coarsely
serrate. Fruit not so long, and more ovate, with much larger and thinner
scales, the lobes hardly spreading. A large tree, 50 to 90 ft. high,
with yellowish or silvery-gray bark peeling off into very thin, filmy
layers from the trunk. Wood whiter, and not so useful. Rich, moist
woodlands, especially northward; also cultivated.

[Illustration: B. nigra.]

6. =Betula nigra=, L. (RIVER OR RED BIRCH.) Leaves 2 1/2 to 3 1/2 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. ALNUS.=

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 deg. 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.

[Illustration: A. incana.]

1. =Alnus incana=, 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 deg. N. Lat.; sometimes cultivated.

[Illustration: A. serrulata.]

2. =Alnus serrulata=, Willd. (