﻿Trees of New York State 357 



Leaves alternate, simple, ovate, acute or acuminate, cordate or rounded at 

 the base, petioled ; stipules strap-shaped to oblong-obovate. Flowers monoe- 

 cious, vernal ; staminate flowers in pendant aments which appear from buds 

 produced the previous season, naked, consisting of several stamens wth 

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

 acute, nearly sessile scales; pistillate flowers in slender, few-flowered aments 

 terminal on leafy branchlets of the j^ear, 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 

 and attached at the base until maturity to a large, foliaceous, 3-lobed, pale 

 green involucre formed by the union of the accrescent bract and braeteoles. 



THE BIRCHES. Geniis BETIJLA L. 

 The genus Betula 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. 

 8ome are large ornamental trees with white or silvery, laminated, 

 papery bark. Others are reduced to scraggl3^ nearly resupinate 

 shrubs and are confined to subarctic regions or alpine summits. 

 Thirteen species occur in North America, ten of which have 

 become arborescent. 



Leaves alternate, simple, serrate or dentate, petioled. Flowers monoecious, 

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

 dulous, solitary or clustered, sessile aments which are preformed the previous 

 season and remain erect and naked on the twigs during the winter, borne in 

 groups of 3 under a peltate bract and two braeteoles, each flower consisting 

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

 calyx of a single sepal: pistillate flowers without perianth, borne in clusters 

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

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

 aments which terminate short, lateral, 2-leaved branches; pistil cinisisting of 

 a, compressed sessile ovary terminated by 2 spreading persistent styles which 

 are stigmatic at the ai>ex. Fruit an erect, inclined or pendant, oblong or 

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

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

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



KEY TO THE SPECIES page 

 1. Leaves with 0-11 pairs of lateral veins; strobiles oblong-ovoid; bark of branch- 

 lets aromatic 2 



1. Leaves with 5-9 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 KU 



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



pubescent; bark silvery-gray, exfoliating in' thin layers B. lutea 163 



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



reddish brown, exfoliating' in thin persistent scales B. nigra 1(55 



