113 



KEY TO THE SPECIES. 



Page. 

 1. Bark usually separating Into thin film-like papery layers 2 



1. Bark close, not separating into thin film-like papery layers, 4 



2. Outer bark white in color, B. alba var. papyriffcra 114 



2. Outer bark not white in color. 3 



3. Outer bark yellow in color; strobiles usually sessile; leaves usually rounded at 



base , ; ; B. lutea 115 



3, Outer bark reddish-brown, close, inner bark tinged with red; strobiles slender- 



stalked; leaves usually wedge-shaped at base B. nigra 116 



4. Bark chalky white covered with black triangular spots below insertion of lateral 



branches; small tree, often in clumps; leaves long-acuminate, B. populifolia 117 



4. Bark dark reddish-brcwn; large tree, usually occurs singly; leaves ovate with acute 



apex; twigs and inner bark with wintergreen-like taste, i..... B, lenta 1H 



8 



