436 



Butler : The western American birches 



15- 



M 



A small tree with silvery gray purple-tinged bark with nearly 

 black lenticels 1-4 cm. long, inner bark pale purple-brown to dark 

 brown, separating with difficulty into shreds but not into sheets, 

 outer bark very thin and semi-transparent, peeling into flakes, the 

 old bark much roughened by peeling into shreds displaying the 

 purplish inner layers j branchlets red-brown, glabrous or slightly 

 puberulent, often covered with a bluish glaucous bloom, becoming 

 brown or gray, usually shining red-brown, with very small, pale 



FiGUUE 15. Behila subcordata Rydb. From type, /. //. Sandberg 32, Nez 

 Terces Co., Idaho. 



conspicuous lenticels and very rarely with minute resinous glands, 

 the older branches red-brown, shining, the lenticels pale, numerous 

 and conspicuous ; leaf-blades ovate, 5-10 cm. long, 4-8 cm. wide, 

 with acute apex and rounded to cordate base, thick, dull, bronze- 

 green above, dull and paler beneath, with 5-7 pairs of prominent 

 pale brown, nearly white veins, glabrous above and below except 

 along veins and midrib, rarely slightly pubescent at the base, finely 

 or coarsely serrate with sharp spreading teeth which are mostly 

 ovate with abruptly pointed tips and 2-4 mm. broad at the base ; 

 petioles 1-2.5 cm. long, stout, pubescent at first or glabrous; 

 fruiting ament 3-4 cm. long, 6-10 mm. thick, cylindrical or ob- 

 long, its stalk more slender than the leaf-petiole, 1-1.5 cm. long, 

 glabrous or slightly resin-dotted ; bractlets 6-8 mm. long, 3-4 

 mm. wide, finely pubescent and ciliate, middle lobe narrow, acute 

 or obtuse, a little longer than the spreading, obliquely rhombic or 



