6o8 



BETULACEAE. 



Vol. I. 



6. B. 



7. B. lutea. 



8. B. fontinalis. 



9. B. glandulosa. 



10. B. Sandbergi. 



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. 



1. B. populifolia. 

 Leaves dull green ; bark readily peeling, white to bronze. 2. B. coerulea. 



Leaves merely acute ; bark white to bronze, readily peeling. 3. B. papyrifera. 



Fruiting aments tomentose. 4. B. nigra. 



Fruiting aments sessile. 



Fruiting bracts 2"-254" long; leaves mostly cordate. 



Fruiting bracts glabrous ; bark dark brown, close. 5. B. lenta. 



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

 Fruiting bracts 3}4"-5" 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. 11. B.pumila. 



Leaves glabrous; at least the upper fruiting bracts entire. 12. B.nana. 



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 i£° ; 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 lobe'd, obtuse or trun- 

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

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

 long; pistillate aments cylindric, in fruit 0/-18" 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 lbs. Leaves tremulous 

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

 birch. Broom- or pin-birch. May. 



I. 



2. Betula coerulea Blanchard. 

 H95- 



Blue Birch. 



Fig. 



Betula coerulea Blanchard, Betula 1. 1904. 

 B. coerulea-grandis Blanchard, loc. cit. 1904. 



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 1' long; staminate aments ii'-3' long; 

 pistillate aments cylindric, about 1' 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- 



