: S. longifolia.]

14. =Salix longifolia=, Muehl. (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. POPULUS.=

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.

[Illustration: P. alba.]

1. =Populus alba=, 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 pro