4. =Bétula lénta=, L. (SWEET, BLACK OR CHERRY BIRCH.) Leaves and bark very sweet, aromatic. Leaves ovate or ovate-oblong, with more or less heart-shaped base, very acute apex, and doubly and finely serrate margin, bright shining green above, smooth beneath, except the veins, which are hairy. Fruit 1 to 1¼ in. long, cylindric, with spreading lobes to the scales. A rather large tree, 50 to 70 ft. high, with bark of trunk and twigs in appearance much like that of the garden Cherry, and not splitting into as thin layers as most of the Birches. Wood rose-colored, fine-grained. Moist woods, rather common throughout; also cultivated. [Illustration: B. lùtea.] 5. =Bétula lùtea=, 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. 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. [Illustration: A. incàna.]