196 



TREES OF NORTH AMERICA 



Leaves ovate, wedge-shaped to truncate or rounded at the base, dull blue-green ; 

 bark white tinged with pink, lustrous, not easily separable into thin layers. 



5. B. ccerulea (A). 

 Scales of the strobiles with ascending or spreading lateral lobes, the middle lobe 

 usually acuminate, longer than broad ; leaves acute or acuminate, their petioles 

 more or less stout. 



Bark separating freely into thin layers. 

 Bark creamy white and lustrous. 



Leaves ovate, dull dark green ; scales of the strobiles glabrous. 



6. B. papyrifera (A, F). 

 Bark reddish brown to grayish white ; scales of the strobiles ciliate. 



Leaves ovate, mostly rounded or cordate at the broad base ; scales of the 

 strobiles puberulous. 7. B, occidentalis (B). 



Leaves ovate, cuneate ; scales of the strobiles glabrous except on the mar- 

 gins ; young branches not or only slightly glandular. 



8. B. Kenaica (B). 

 Leaves rhomboidal to deltoid ; scales of the strobiles glabrous except on 

 the margins ; young branchlets thickly covered with glands. 



9. B. Alaskana (A, B). 

 Bark not separable into thin layers, dark brown ; scales of the strobiles 

 glabrous or puberulous. 



Leaves ovate, truncate or rounded at the broad base, dull green. 



10. B. fontinalis (B, F, G). 



1. Strobiles oblong-ovoid, erect; wing not broader than the nut ; leaves with 9-11 pairs 

 of veins. 



1. Betula lenta, L. Cherry Birch. Black Birch. 



Leaves ovate to oblong-ovate, acute or acuminate, gradually narrowed and often 

 unequal at the cordate or rounded base, sharply serrate, with slender incurved teeth, 

 when they unfold light green, coated on the lower surface and the margins with 



long white silky hairs, and slightly hairy on the upper surface, at maturity thin and 

 membranaceous, dark dull green above, light yellow-green below, with small tufts 

 of white hairs in the axils of the veins, 2 ^'-6' long, 1^-3' wide, with yellow midribs 

 and primary veins prominent and hairy on the lower surface, and obscure reticulate 



