82- 



witli the appearance of the leaves, pistillate eatkins ovoid or cyliiidrie; 

 fruit a small winged fiat seed, liearing- at the a]iex the two persistent 

 stigmas. 



Bark of twigs usually with a slight wintergreeii tia\or; lea\'es 

 with 7-1.5, usually 9-11 pairs of prominent veins; rounded 

 or slightly cordate at the base; fertile eatkins generally 



10 mm. or more in diameter 1 B. lutea. 



Bark of twigs iisually bitter, not wintergreen fla'S'ored; leaves 

 with 4-11, tisually 4-9 pairs of prominent veins, more or 

 less obtusely angled at the liase; fertile eatkins generally 

 less than 10 mm. in diameter (rarely 10 mm. or mor(>, 

 B. nigra). 

 Bark of trtiuk ehalky-white; fruiting aments drooping or 

 s]ireading. 

 Bark' below base of lateral lu'aiiehes tlarkened-triaugular in 

 outline; lea\'es long acuminate and lustrous above; 



slaniinate catkins usually solitary 2 B. populifolia. 



Bark below base of lateral branches not darkened; leaves 

 o\'ate and not lustrous above; staminate eatkins usually 



2-3 3 B. papyrifera. 



Bark of trunks dark; fruiting aments erect or nearly so 4 B. nigra. 



1. Bclula lutea Miehatix filius. Birch. Yellow Birch. Plate 

 .32. ^Medium size trees; bark of small trees and of the branches of old 

 trees smooth, silver or dark grav', freely peeling off in thin strips, be- 

 coming on older trees a dark lirown, rarely tight, usually fissured into 

 wide plates and rolling l)ack from one edge; the shoots of the j'ear hairy, 

 greenish gray, becoming glabrous or nearly so and reddish-brown by the 

 end of the second year, not aromatic when bruised but when chewetl 

 sometimes a faint wintergreen odor can be detected; winter buds 

 pointed, icddish-brown, the lower scales more or less pubescent, gener- 

 ally with a fringe of hairs on the margins; leaves usually appearing in 

 paii's, ovate to o^'ate-oblong, 4-14 cm. long, taper-]K)inted, 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 maturitj' glabrous or nearly so above, and remaining 

 moi-e or less pubescent below, especially on the veins, both surfaces 

 with few to numerous resinous dots; petioles permanently hairy, 

 generalljf 5-13 mm. long; flowers apjiear m 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 leddish- 

 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 



