328 FLORA. 



with the fruits; perianth none; ovary sessile, 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, 

 natives of the north temperate and arctic zones. 



* Trees. 

 Fruiting aments peduncled ; bark chalky-white. 



Leaves deltoid, acuminate ; lateral lobes of fruiting bracts'short, divergent. 



1. B. populifolia. 

 Leaves ovate or suborbicular ; lateral lobes of the fruiting bracts ascending. 



2. B. papyri/era. 

 Fruiting aments peduncled ; bark greenish-brown or brown. 



Western ; leaves ovate, often obtuse at the base. 3. B. occidentalis. 



Eastern ; leaves rhombic, acute at both ends. 4. B. nigra. 



Fruiting aments sessile, at the ends of short branches ; bark brown or yellowish. 

 Fruiting bracts 4 mm. long, lobed at the apex ; leaves shining above. 



5. B. lenta. 

 Fruiting bracts 8 mm. long, lobed to about the middle ; leaves dull above. 



6. B. lutea. 

 ** Shrubs. 



Twigs glandular-warty ; leaves glabrous. 7. B. glandulosa. 

 Twigs not glandular-warty, glabrous or pubescent. 



Leaves glabrous ; upper fruiting bracts mostly entire. 8. B ' , nana. 



Young foliage densely pubescent ; bracts 3-lobed. 9. B. pumila. 



1. Betula populifolia Marsh. AMERICAN WHITE BIRCH. (I. F. f. 1211.) A 

 slender tree, with white smooth bark, tardily separating in thin sheets; twigs russet, 

 warty. Leaves deltoid, pubescent on the veins when young, nearly glabrous when 

 old, minutely glandular, long-acuminate, sharply dentate and commonly somewhat 

 lobed, obtuse or truncate at the base, 3-6 cm. long, slender-petioled; staminate 

 aments 5-8 cm. long; pistillate aments cylindric, in fruit 1.5-3.6 cm. long, slender- 

 peduncled; fruiting bracts puberulent, 2-4 mm. long, their lateral lobes larger than 

 the middle one; nut narrower than its wings. In moist or dry soil, N. B. to S. 

 Ont. and Del. Leaves tremulous like those of the Aspens. May. 



2. Betula papyrifera Marsh. PAPER OR CANOE BIRCH. (I. F. f. 1212.) A 

 large forest tree. Bark chalky white, peeling in thin layers. Leaves ovate, acute 

 or acuminate, dentate and denticulate, glabrous above, glandular and pubescent 

 on the veins beneath, slender-petioled, 3-11 cm. long; petioles 1-3 dm. long; stam- 

 inate aments 5-10 cm. long; pistillate aments cylindric, slender-peduncled, 2-5 

 cm. long; fruiting bracts 4-6 mm. long, puberulent or ciliate; nut narrower than 

 its wings. Newf. to Alaska, Penn., Mich., Neb. and Wash. April-May. 



Betula papyrifera minor Tuckerm. A low bushy form, occurring on the higher 

 mountains of N. E. and N. N. Y. 



3. Betula occidentalis Hook. WESTERN RED BIRCH. (I. F. f. 1213.) A 

 tree, the bark smooth, dark bronze, the twigs gray-brown, warty. Leaves broadly 

 ovate or nearly orbicular, sharply serrate, short-petioled, glabrous on both sides 

 or sparingly pubescent beneath, 2-5 cm. long; pistillate aments peduncled, cylin- 

 dric, 2-3 cm. long, about I cm. in diameter in fruit; fruiting bracts ciliolate, about 

 6 mm. long, their lateral lobes ascending; nut much narrower than its wings. 

 W. Neb. to Br. Col., Cal. and N. Mex. April-May. 



4. Betula nigra L. RIVER BIRCH. RED BIRCH. (I. F. 1214.) A slen- 

 der tree; bark reddish or greenish-brown, peeling in very thin layers; twigs red- 

 dish. Young shoots, petioles and lower surfaces of the leaves tomentose; leaves 

 rhombic-ovate, irregularly serrate or somewhat lobed, base cuneate, when mature 

 dark green above, pale beneath, 38 cm. long; petioles 6 16 mm. long; staminate 

 aments mostly clustered in 2's or 3's, 6-9 cm. long; pistillate aments oblong- 

 cylindric, spreading, peduncled, 2-5 cm. long, 10-12 mm. in diameter in fruit; 

 fruiting bracts tomentose, about equally 3-lobed; nut broadly obovate, wider than 

 its wings. Along streams and lakes, Mass, and N. H. to Iowa, Kans., Fla. and Tex. 



. April-May. 



5. Betula lenta L. CHERRY, BLACK OR SWEET BIRCH. (I. F. f. 1215.) 

 A large forest tree, with dark brown close smooth bark, becoming furrowed, not 



