12. =Sàlix díscolor, Mühl.= (GLAUCOUS OR BOG WILLOW.) Leaves lanceolate or ovate-lanceolate, acute, remotely serrate at the base, finely serrate along the middle, and almost entire near the tip; smooth and bright green above, soon smooth and somewhat glaucous beneath; stipules, on the vigorous shoots, equaling the petiole, more frequently small and inconspicuous. Catkins sessile, 1 in. long, appearing before the leaves in the spring; scales dark red or brown, becoming black, covered with long glossy hairs. Fruit in catkins, 2½ in. long, the capsules very hairy, with short but distinct style. A very variable species, common in low meadows and on river-banks; usually a shrub, but occasionally 15 ft. high. [Illustration: S. cinèrea.] 13. =Sàlix cinèrea, L.= (GRAY OR ASH-COLORED WILLOW.) Leaves obovate-lanceolate, entire to serrate; glaucous-downy and reticulated with veins beneath; stipules half heart-shaped, serrate. Flowers yellow; ovary silky, on a stalk half as long as the bracts. A shrub to middle-sized tree, 10 to 30 ft. high, with an erect trunk; occasionally cultivated; from Europe. [Illustration: S. longifòlia.] 14. =Sàlix longifòlia=, Mühl. (LONG-LEAVED WILLOW.) Leaves linear-lanceolate, very long, tapering at each end, nearly sessile, remotely notched with projecting teeth, clothed with gray hairs when young; stipules small, lanceolate, toothed. Branches brittle at base. A shrub or small tree, 2 to 20 ft. high, common, especially westward, along river-banks. GENUS =92. PÓPULUS.= Trees with alternate, deciduous, broad-based leaves. Flowers in long and drooping catkins, appearing before the leaves are expanded in the spring. Fruit small, dry pods in catkins, having seeds, coated with cottony down, which early in the season escape and float in the wind. On this account the trees are called Cottonwoods in the West. Trees with light-colored, rather soft wood. * Leaves always white-hairy underneath; more or less deeply lobed; buds not gummy 1. * Leaves smooth beneath, at least when old. (=A.=) =A.= Leafstalk decidedly flattened laterally. (=B.=) =B.= Buds not covered with sticky gum. (=C.=) =C.= Leaves roundish heart-shaped; bark on trunk greenish-white, 2. =C.= Leaves large, ovate, with large, irregular, sinuate teeth, 3. =B.= Buds covered with aromatic, glutinous resin. (=D.=) =D.= Tree tall, spire-shaped, 5. =D.= Not very spire-shaped; young twigs sharply angled or winged, leaves 6 to 10 in. long, broadly deltoid, serrate with incurved teeth, 6. =D.= Not spire-shaped; young twigs not angular, 7. =A.= Leafstalk not decidedly flattened; leaf-margin crenate. (=E.=)