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.)
E. Buds not glutinous; leaves white-woolly beneath when young, 4.
E. Buds very glutinous; leaves large, shining green on both sides, 8.

P. álba.

1. Pópulus álba, L. (White Poplar or Abele Tree.) Leaves roundish, slightly heart-shaped, wavy toothed or lobed, soon green above, very white-cottony beneath even when old; buds without the sticky coating common in the genus. Branches very white with down when young. Root creeping and producing numerous suckers. A large tree, 50 to 80 ft. high, of rapid growth, often cultivated; from Europe. Leaves and branches very variable, forming several named varieties in the catalogues of the nurseries.

P. tremuloìdes.