82 



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 IB. 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 lutea 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, be- 

 coming 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 red dish-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, gener- 

 ally 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 



