Butler : The western American birches 



431 



middle lobe acute, narrowly triangular, much longer than the as- 

 cending, acute, obliquely rhombic lateral ones ; samara wings much 

 wider than the ovate or obovate puberulous nutlet. [Figure 9.] 



This is one of the most common birches of the West, being 

 found throughout the Rocky Mountain region and readily dis- 

 tinguished by Its densely resinous slender branchlets, its smooth, 



shining reddish bark and small broadly ovate acute shining leaves. 

 It is often called cherry birch and has been confused with Beiida 

 occidentalis through a mistake of Hooker's (Fl. Bor.-Am. 2: 155) 

 in confusing the large western tree form with this, which is usually 

 small and shrub-like, forming clumps hke willows along streams. 

 Sargent's explanation (Bot. Gaz. 31 : 239) is doubtless 

 and his name for the species very aptly chosen. 



correct 



10. Betula kenaica Evans, Bot. Gaz. 27: 481. 1899 



A tree up to 13 m. in height with thin dark brown bark sepa- 

 rable into layers; twigs glandular-resiniferous, though not densely 

 so, red-brown and shining ; leaf-blades about 6 cm, long, nearly 

 as wide, ovate, slightly hairy when young, soon becoming gla- 



FiGURE 10. Bettila kenaica Evans 



Figure 9. Betula fontinalis _ 



Sarg. From^. T, Butler 32^, From C. V, Piper 44So,YiQr\2S, Alaska. 



near Helena, Montana. 



brous, dull dark green above, paler beneath, acute at apex, obtuse 

 or nearly truncate at base, sharply, coarsely, and irregularly serrate, 



