Trees of New York State 357 



Leaves jilfcriiatc, siiii|ilc, (i\;it(», acute or acuiiiinutc, cordate or rounilcil ;it 

 the base, jjctioled ; .stipules strap-sliajied to ohloujir-ohovate. Flmccrs monoe- 

 cious, venial; staniiuate Howers in pendant aments which ajipear from buds 

 produced the previous season, iiaked, consisting of several stamens w-ith 

 bifurcated filaments terminated by anthers borne in the axils of broadly ovate, 

 acute, iie.-uly sessile scales; pistillate flowers in slender, few-flowered aments 

 terminal on leafy branchlets of the year, in pairs at the base of an ovate, 

 acute, leafy, deciduous scale, each pair subtended by a bract and two bract- 

 lets; calyx adnate to the 2-celled ovary; stigmas 2, subulate. Fruit a small, 

 acute, compressed, longitudinally-ribbed nutlet, tipped with the calyx-lobes 

 .•nid attached at the ba.se until maturity to a large, foliaceous, 3-lobed, pale 

 green involucre formed liy the union of the accrescent bract and bracteoles. 



THE BIRCHES. Gemis BETULA L. 

 The genus Bittda is represented by .some thirty odd species of 

 aromatic trees and shrubs scattered through the subarctic and 

 north temperate zones in Europe, Asia, and North America. 

 Some are lai'ge oi'namental trees \vith Avhite or silvery, laminated, 

 jiapery bark. Others are reduced to scraggly, nearly resupinate 

 sliru])s and are confined to subarctic regions or alpine summits. 

 Thirteen species occur in North America, ten of which have 

 l)eeome arborescent. 



Leaves alternate, simple, serrate or dentate, ])etioled. Flowers monoecious, 

 unfolding with or before the leaves, anomopliilous ; staminate flowers in pen- 

 (iuldus. solitary (ir clustered, scssili' aiiu'iils wliidi ;ire preformed the previous 

 season ami remain erect and luiked on the twigs during the wnter, borne in 

 groups of 3 under a peltate bract an<l two ])racteoles, each flower consisting 

 of 2 2-parted filaments terminating in anther sacs and accompanied by a 

 c.'ilyx of a single sepal : pistillate flowers without perianth, borne in clusters 

 of 3 subtended by a 3-lobed, persistent accrescent scale, the mmy closely- 

 imbricated scales forming short, oblong or cylindrical, usually &liort-stalked 

 .'iinents which terminate short, lateral, 2-leaved branches; pistil consisting of 

 a compressed sessile ovary terminated by 2 spreading pei'sistent styles which 

 are stigmatic at the apex. Fruit an erect, inclined or pendant, oblong or 

 oblong-ovoid strobile consistmg of thin, woody, 3-lobed, imbricated scales, 

 each bearing 3 laterally-winged, compressed nutlets; at maturity the scales 

 fall away from the jiersistent cone-axis, releasing the nutlets. 



KEY TO THE SPECIES page 

 1. Leaves with 9-11 pairs of lateral veins; strobiles oblong-ovoid; bark of branch- 

 lets aromatic 2 



1. Leaves with .'3 9 pairs of veins; strobiles cylindrical or oblong; bark of branch- 

 lets not aromatic 3 



2. leaves heart-shaped at the base; strobile-scales smooth; bark dark brown, 



close B. lenta IGl 



2. Leaves cuneate or slightly heart-shaped at the base; strobile-scales 



pubescent; bark silvery-gray, exfoliating in'thin layers B. lutea lfi3 



3, Leaves rhombic-ovate; .strobiles oblong, ripening in May or June; bark light 



reddi.sh brown, exfoliating' in thin persistent scales B. nigra 165 



