6o8 



BETULACEAE. 



VOL. I. 



B. coerulea. 

 B. papyrifera. 

 B. nigra. 



sile, 2-celled ; styles 2, stigmatic at the apex, mostly persistent. Nut small, compressed, 

 membranous-winged on each side (a samara), shorter than the bracts. [The ancient name.] 



About 35 species of the north temperate and arctic zones. Type species : Betula alba L. 

 Trees (except mountain and boreal races of no. 3). 

 Fruiting aments peduncled. 



Fruiting aments not tomentose. 

 Leaves long-acuminate. 



Leaves bright green, irregularly toothed ; bark not readily peeling, chalky white. 



i. B. populifolia. 



Leaves dull green ; bark readily peeling, white to bronze. 

 Leaves merely acute ; bark white to bronze, readily peeling. 

 Fruiting aments tomentose. 

 Fruiting aments sessile. 



Fruiting bracts 2" -2^/2" long; leaves mostly cordate. 

 Fruiting bracts glabrous ; bark dark brown, close. 

 Fruiting bracts ciliate ; bark gray to yellow brown, close or peeling. 

 Fruiting bracts 3 J^"-s" long, ciliate; bark yellow-gray, freely peeling. 

 Shrubs (nos. 8 and 10 sometimes forming small trees). 

 Twigs glandular-warty. 



Samara-wings broader than the nut. 

 Samara-wings narrower than the nut. 

 Twigs not glandular-warty. 



Samara-wings-broader than the nut. 

 Samara-wings narrower than the nut. 



Young foliage densely pubescent ; fruiting bracts all 3-lobed. 

 Leaves glabrous ; at least the upper fruiting bracts entire. 



5. B. lenta. 



6. B. alleghanensis. 



7. B. lutea. 



8. B. fontinahs. 

 g. B. glandulosa. 



10. B.Sandbergi. 



1 1. B. pumila. 



12. B. nana. 



i. Betula populifolia Marsh. American White Birch. Fig. 1494. 



Betula populifolia Marsh. Arb. Am. 19. 1785. 

 B. alba var. populifolia Spach, Ann. Sci. Nat. (II.) 15: 

 187. 1841. 



A slender tree with very white smooth bark, tardily 

 separating in thin sheets ; maximum height 45 ; trunk 

 diameter ij ; the twigs russet, warty. Leaves deltoid, 

 pubescent on the veins when young, nearly glabrous 

 when old, minutely glandular, bright green above, light 

 green beneath, long-acuminate, sharply irregularly 

 dentate and commonly somewhat lobed, obtuse or trun- 

 cate at the base, ii'-2i' long, i'-2' wide, slender- 

 petioled ; petioles channeled ; staminate aments 2' -3' 

 long; pistillate aments cylindric, in fruit g"-iS" long, 

 3"-S" in diameter, slender-peduncled ; fruiting bracts 

 puberulent, i"-2" long, lateral lobes divergent, larger 

 than the middle one; nut narrower than its wings. 



In moist or dry soil, Nova Scotia to southern Ontario, 

 Pennsylvania and Delaware. Wood soft, weak, light 

 brown ; weight per cubic foot 36 Ibs. Leaves tremulous 

 like those of the aspens. Gray-, poverty- or old-field- 

 birch. Broom- or pin-birch. May. 



2. Betula coerulea Blanchard. Blue Birch. 

 Fig. 1495- 



Betula coerulea Blanchard, Betula i. 1904. 

 B. coerulea-grandis Blanchard, loc. cit. 19.04. 



A tree, attaining a maximum height of about 65 and 

 a trunk diameter of 2, the bark white, readily peeling 

 off in thin layers, the young twigs somewhat pubescent, 

 becoming glabrous. Leaves ovate, 2'-4*' long, serrate, 

 long-acuminate -at the apex, broadly cuneate at the base, 

 when mature glabrous and dull bluish-green above, 

 slightly pubescent on the veins beneath, the petioles 

 slender, about i' long; staminate aments ii'-3' long; 

 pistillate aments cylindric, about i' long, on stalks about 

 one-half as long; fruiting bracts with divergent lateral 

 lobes ; nut much narrower than its wings. 



Hillsides, Quebec to Manitoba, Maine and Vermont, 

 sembles the European Betula pendula Roth. 



Re- 



