206 TREES OF NORTH AMERICA 



CONSPECTUS OF THE NORTH AMERICAN ARBORESCENT SPECIES. 



Strobiles oblong-ovoid, nearly sessile, erect, the lateral lobes of their scales broad and slightly 

 divergent; wing not broader than the nut; leaves with 9-11 pairs of veins; bark of young 

 branches aromatic. 



Leaves heart-shaped or rounded at base; scales of the strobiles glabrous; bark dark 

 brown, not separating into thin layers. 1. B. lenta (A, C). 



Leaves cuneate or slightly heart-shaped at base; scales of the strobiles pubescent; bark 

 yellow, or silvery white, rarely dull yellowish brown; separating into thin layers. 



2. B. lutea (A). 

 Strobiles oblong or cylindric, erect, spreading or pendant, on slender peduncles; wing 



broader than the nut; leaves with 5-9 pairs of veins. 



Strobiles oblong, erect, ripening in May or June, their scales pubescent, deeply lobed, the 

 lateral lobes erect; leaves rhombic-ovate, glaucescent and more or less silky-pubescent 

 beneath; bark light reddish-brown, separating freely into thin persistent scales. 



3. B. nigra (A, C). 

 Strobiles cylindric, pendant or spreading. 



Scales of the strobiles pubescent, with recurved lateral lobes, the middle lobe triangu- 

 lar, nearly as broad as long; leaves long-pointed; petioles slender, elongated. 

 Leaves triangular to rhombic, bright green and lustrous; bark chalky white, not 

 separable into thin layers. 4. B. populifolia (A). 



Leaves ovate, cuneate to truncate or rounded at base, dull blue-green; bark white 

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



5. B. cxfirulea (A). 



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

 ally acuminate, longer than broad; leaves acute or acuminate. 

 Bark separating freely into thin layers; scales of the strobiles glabrous. 

 Bark creamy white, or in some forms orange-brown; leaves ovate. 



6. B. papyrifera (A, B, C, F). 

 Bark dull reddish brown or nearly white; leaves rhombic to deltoid-ovate. 



7. B. alaskana (A, B). 

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



or puberulous; branchlets glandular. 

 Leaves ovate, acute or acuminate, truncate or rounded at the broad base. 



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



Leaves broad-ovate to elliptic, acute, rounded or abruptly short-pointed, cuneate 

 at base. 9. B. Eastwoodae'(F). 



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



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

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

 rarely laciniately lobed (f . laciniata Rehdr.), when they unfold light green, coated on the 

 lower surface with long white silky hairs, and slightly hairy on the upper surface, at ma- 

 turity 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, l%'-3' wide, with a yellow mid- 

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

 cross veinlets; turning bright clear yellow late in the autumn; petioles stout, hairy, deeply 

 grooved on the upper side, f'-l' long; stipules ovate, acute, light green or nearly white, 

 scarious and ciliate above the middle. Flowers : staminate aments during the winter about 

 f ' long, nearly |' thick, with ovate acute apiculate scales bright red-brown above the middle 

 and light brown below it, becoming 3'-4' long; pistillate aments '-f ' long, about f ' thick, 

 with ovate pale green scales rounded at the apex; styles light pink. Fruit: strobiles ob- 

 long-ovoid, sessile, erect, glabrous, I'-l^' long, about %' thick; nut obovoid, pointed at 

 base, rounded at apex, about as broad as its wing. 



