=3. BÉTULA.= The Birches.
Trees and shrubs with bark tight, scaly or separating into very thin
plates and peeling off transversely, whitish or dark colored; staminate
catkins developing in autumn and dehiscing in early spring before or
with the appearance of the leaves, pistillate catkins ovoid or
cylindric; fruit a small winged flat seed, bearing at the apex the two
persistent stigmas.
Bark of twigs usually with a slight wintergreen flavor;
leaves with 7-15, usually 9-11 pairs of prominent
veins; rounded or slightly cordate at the base;
fertile catkins generally 10 mm. or more in
diameter. 1 B. lutea.
Bark of twigs usually bitter, not wintergreen flavored;
leaves with 4-11, usually 4-9 pairs of prominent
veins, more or less obtusely angled at the base;
fertile catkins generally less than 10 mm. in
diameter (rarely 10 mm. or more, _B. nigra_).
Bark of trunk chalky-white; fruiting aments drooping
or spreading.
Bark below base of lateral branches darkened-triangular
in outline; leaves long acuminate and lustrous
above; staminate catkins usually solitary. 2 B. populifolia.
Bark below base of lateral branches not darkened;
leaves ovate and not lustrous above; staminate
catkins usually 2-3. 3 B. papyrifera.
Bark of trunks dark; fruiting aments erect or
nearly so. 4 B. nigra.
=1.= =Betula lùtea= Michaux filius. Birch. Yellow Birch. Plate 32.
Medium size trees; bark of small trees and of the branches of old trees
smooth, silver or dark gray, freely peeling off in thin strips, becoming
on older trees a dark brown, rarely tight, usually fissured into wide
plates and rolling back from one edge; the shoots of the year hairy,
greenish gray, becoming glabrous or nearly so and reddish-brown by the
end of the second year, not aromatic when bruised but when chewed
sometimes a faint wintergreen odor can be detected; winter buds pointed,
reddish-brown, the lower scales more or less pubescent, generally with a
fringe of hairs on the margins; leaves usually appearing in pairs, ovate
to ovate-oblong, 4-14 cm. long, taper-pointed, oblique and wedge-shape,
rounded or slightly cordate at the base, sharply and rather coarsely
serrate, hairy on both sides when they appear, becoming at maturity
glabrous or nearly so above, and remaining more or less pubescent below,
especially on the veins, both surfaces with few to numerous resinous
dots; petioles permanently hairy, generally 5-13 mm. long; flowers
appear in May; staminate spikes in clusters at the ends of the branches,
about 6 cm. long, scales broadly ovate, blunt, fringed with hairs,
green-tipped with a margin of reddish-brown; pistillate spikes solitary
in the axils of the leaves, mature spikes 2.5-5 cm. long, generally
2.5-3 cm. long, commonly about half as thick as long, recurved to
ascending, commonly about horizontal, sessile or on short stalks; scales
very variable, 5-11 mm. long, generally 7-8 mm. long, sometimes as wide
as long but generally about one-fourth longer than wide, densely
pubescent on the back, or rarely glabrous on the back, ciliate, glabrous
or nearly so on the inside, commonly with a few brown or black glands on
the margin, commonly lobed to more than one-third of their length, lobes
ascending or divaricate, the lateral generally the larger and almost as
long as the narrower middle lobe; nuts divested of the wings, slightly
obovate, about 3 mm. long, wings about two-thirds as wide as the nut and
usually with a fringe of hairs at the blunt apex.
[Illustration: Plate 32.