Butler : The western American birches 437 



rounded lateral lobes ; samara wings mostly broader than the more 



or less puberulent nutlet. [Figure 15.] 



The type is J. H. Sandberg's jj from Hatwai Creek, Nez 

 Perces Co., Idaho. It is common throughout the Rocky Moun- 

 tains west of the main divide from Idaho and Montana northward 



r 



into British Columbia and Alberta. It differs from B, papyrifera 

 in the color and character of the bark, the form and toothing of 

 the leaves, the character of the bractlets, and in the glabrous 

 branchlets ; from B. occidentalis in the above characters and also 

 in having thicker dull green leaves. It stands between these spe- 

 cies, but is wholly distinct from either. It has also been called B. 

 cordifolia Regel, but that species has laciniately cut leaves, which 

 are also larger with usually 8 pairs of veins, slightly lobed, with 

 long-pointed apex and slightly cordate base, petioles and venation 

 hairy, bark white and peeling readily, bractlets quite unlike B, 

 subcordata in form and almost glabrous, with lobes all rounded and 

 about equal in width, the middle twice as long as the ascending 

 lateral ones. 



J I 



16. Betula occidentalis Hook., in part, Fl. 



-Bor.-Am. 2: 155. 1839 



A large tree reaching 40 m, in height in the type locality (the 

 region about Puget Sound); bark yellow-brown, orange, or dark 

 bronze-brown, outer layer very thin and peeling into small curling 

 shreds, inner layers varying from pale tan to dark reddish-brown, 

 separable into layers though often with difficulty and not until 

 old ; branchlets usually very glandular-resiniferous, sometimes 

 hairy or puberulent, slender, pale brown, becoming dark, gla- 

 brous, and lustrous; leaf-blades 6— 10 cm. long, 5-6 cm. wide, 

 ovate, with acute or acuminate apex and truncate or rounded, 

 occasionally subcordate or subcuneate base, furnished with 7 or 8 

 pairs of coarse brown or yellowish veins, doubly serrate with 

 Irregular, very slender, long-pointed teeth, slightly lobed, bright 

 green, glabrous, or puberulent beneath, resinous when young. 

 hairy along the venation beneath with tufls of hairs in the vein- 

 axils ; petioles 1-2 cm. long, hairy or puberulent, becoming gla- 

 brous ; fruiting aments 3-4 cm. long, 10-12 mm. thick, cylindri- 

 cal or oblong, on stout stalks 12-18 mm. long; bractlets ciliate, 

 5-6 mm. long, 3-4 mm. wide, broadest at the apex of the widely 

 spreading obliquely ovate or rhombic, rounded, lateral lobes, mid-, 

 die lobe elongated, acute, awl-shaped, claw short, cuneate ; nutlet 

 oval, nearly as wide as the wings. [Figure 16.] 



