BETULACEAE. 329 



separating in layers; twigs smooth, wart}-; young leaves silky. Mature leaves 

 ovate or ovate-oblong, acute or acuminate, the base cordate or rounded, sharply 

 serrulate, bright green, and shining above, pubescent on the veins beneath, 6-10 

 cm. long; petioles 6-12 mm. long; staminate aments clustered, 6-10 cm. long; 

 pistillate aments sessile, dense, oblong, about 2.5 cm. long in fruit, nearly erect; 

 bracts appressed. about 4 mm. long, nearly equally 3dobed, the lateral lobes some- 

 what divergent; nut oblong, broader than its wings. Xewf. to Ont., Fla. and 

 Tenn. April-May. 



6. Betula lutea Michx. f. Yellow Birch. Gray Birch. (I. F. f. 1216.) 

 A large forest tree, similar to the preceding, the bark yellowish or gray, sepa- 

 rating in thin layers or close, the twigs gray-brown. Leaves ovate or oblong-ovate, 

 mostly acuminate at the apex, rounded, obtuse or rarely subcordate at the base, 

 sharply serrulate, dark green and dull above, pubescent on the veins beneath; 

 staminate aments usually 2-4 together; pistillate aments sessile, oblong or oblong - 

 cylindric, rather loose; bracts nearly equally 3-lobed to the middle, ciliolate, the 

 lateral lobes ascending. New£ to Manitoba, N. Car., Ga. and Tenn. April-May. 



7. Betula glandulosa Michx. Glandular or Scrub Birch, (I. F. f. 

 12 1 7.) A shrub, 3-12 dm. high, the twigs brown, glandular-warty, not pubescent. 

 Leaves orbicular, oval or obovate, glabrous, rounded at the apex, crenate-dentate, 

 bright green above, pale and glandular-dotted beneath, short-petioled, 0.6-2.5 cm - 

 long; petioles 2-6 mm. long; staminate aments commonly solitary, 1-1.5 cm. long; 

 pistillate aments cylindric, erect, peduncled, 1-2.5 cm. long and about 4 mm. in 

 diameter in fruit; fruiting bracts glabrous, the lateral lobes divergent, rather 

 shorter than the middle one; nut oblong, usually narrower than its wings. Newf. 

 to Alaska, the higher mountains of Me. and N. X. Y., Mich., Minn., and in the 

 Rocky Mountains to Colo. Also in Asia. June-July. 



8. Betula nana L. Dwarf Birch. (I. F. f/1218.) A low diffuse shrub, 

 similar to the preceding, but the twigs glandless. Leaves orbicular, obovate, or 

 reniform, bright green, firm, deeply and incisely crenulate, rounded at the apex, 

 6-20 mm. long; petioles rarely more than 2 mm. long; staminate aments 1-2.5 

 cm. long; pistillate aments oblong, 6-10 mm. long; fruiting bracts glabrous, the 

 lower usually 3-lobed, the upper ovate or lanceolate, mostly entire; nut oblong, 

 wingless or narrowly winged. Greenland and Lab. to Hudson Bay. Also in 

 northern Europe and Asia. May-June. 



Betula nana flabellifolia Hook. Leaves with a'cuneate base and more deeply 

 incised-crenulate. Lab. and Xewf. 



9. Betula pumila L. Low Birch. (I. F. f. 1219.) A bog shrub, 0.5-5 m - 

 tall, the twigs brown, becoming glabrous, the young foliage densely brownish 

 tomentose. Leaves obovate, broadly oval or orbicular, rounded at both ends or 

 some of them cuneate-narrowed at the base, rather coarsely dentate, when mature 

 glabrous above, pale, persistently tomentose or becoming glabrous beneath and 

 reticulate-veined, 1-3 cm. long; petioles 3-6 mm. long; fruiting aments oblong- 

 cylindric, erect, peduncled, 2.5 cm. long or less; bracts puberulent or ciliolate, the 

 lateral lobes spreading at right angles, shorter than the middle one; nut oblong, 

 mostly rather broader than its wings. Xewf. to Ont., theN. W. Terr., X. J., Ohic 

 and Minn. May -June. 



5. ALNUS Gaertn. 



Shrubs or trees, with dentate or serrulate leaves, few-scaled buds, and flowers 

 of both kinds in aments, expanding before, with or after the leaves, making their 

 first appearance during the preceding season, the staminate pendulous, the pistil- 

 late erect, clustered. Staminate flowers 3 or sometimes 6 in the axil of each bract, 

 consisting of a mostly 4-parted perianth, 4 stamens and subtended by I or 2 bract- 

 lets; filaments short, simple; anther-sacs adnate. Pistillate flowers 2-3 in the axil 

 of each bract, without a perianth, but subtended by 2-4 minute bractlets; ovary 

 sessile, 2-celled; styles 2; bracts woody, persistent, 5 -toothed or erose. Xut small* 

 compressed. [Ancient Latin name derived from the Celtic, in allusion to the 

 growth of these trees along streams.] About 14 species, natives of the northern 

 hemisphere and the Andes of S. Am. Besides the following, some 6 others occur 

 in the western parts of X T . Am. 



