Handbook of Teees of the Northern States and Canada. 427 



bj Broad-ovate, cordate at base, pale or rusty beneath P. candieans. 



b Uvate, pale or rusty beneath, rounded or wide c-uneate at base, finely ereuate-serrate, 



, , TT «<="°i,'"»t''^ • • • P. 'balsaiuifera. 



b 1-leart-shaped, large, abrupt at apex, crenate-seriate and petioles slightly if at all 



flattened p_ hete'rophylla. 



sr Buds not resin-coated ; leaves orbicular-ovate ; petioles long and ' 

 b Flattened laterally (Aspens) and edges of leaves 



Finely crenate-serrate ; buds glabrous p. tremuloides. 



- , „ Coarsely dentate : buds scurfy-pubescent '.'.'.', p. gramdidentata. 



b blightly if at all flattened ; leaves densely white-tomentose beneath. P. alba. 



For species see pp. 91-113 and the following: 



Edkopean Black Poplar, P. nigra L. A large wide-spreading European tree and nearly 

 a century ago was reported (as P. Hudsonieii Michx. and P. hciiiJifolia Pursh.) as naturalized 

 in l:his country, but it is rare in a naturalized state. The characters given below are of the 

 typical P. nigra, and are equally applicable to the Lombardy Poplar (var. Italiea) except as 

 noted in the consideration of that tree. Leaves broad-deltoid, wide-cuneate or almost truncate 

 at base, abruptly acuminate at apex, crenate, pubescent at first but finally glabrous, firm, the 

 blade usually wider than long; petioles long, slender and laterally compressed. Plovers: 

 ■staminate aments l%-3 in. becoming longer; stamens about 20; pistillate aments 2-3 in. long, 

 becoming longer. Fruit: capsules oblong, obtuse, short-stalked. 



BIRCH FAMILY. BETULACE^E. 



Trees and a few shrubs of the northern hemisphere commonly with fragrant aromatic 



properties and grouped in six genera of which five are found in North America. They have 



the following characters in common ; 



hearcs simple, alternate, petioled, pinniveined, obliquely plicate in venation, deciduous ; 

 ■stipules fugacious : branchlets terete. Flowers in early spring before or with the unfolding of 

 the leaves, moncecious ; the staminate in elongated pendulous lateral aments, in the axils 

 of the bracts of which are borne 1-3 small flowers, with or without calyx and 2-20 small 

 -erect stamens inserted on the receptacle, with distinct filaments and 2-celIed extrorse anthers 

 opening longitudinally ; pistillate flowers in short spike-like or capitate aments, from lateral buds 

 with or without calyx, ^vith 2-celled ovary and 2-cleft or bifurcate style stigmatic at the apex 

 •or on the inner surfaces of the branches and a single anatropous pendulous ovule in each 

 cell of the ovary. P'ruit a small mostly 1-celled 1-seeded nut or samara ; seed solitary, 

 suspended, without albumen, with large and fleshy cotyledons and short radicle. 



KEY TO THE GEXEEA. 



,1 Xutlet wingless, from the axils of deciduous scales and more or less inclosed in an 

 involucre ; staminate flowers solitary in the axils of the scales of the ament and without 

 calyx ; involucre of fruit 

 b Flat, open, .3-eleft and foliaceous ; staminate aments in winter inclosed with bud-scales. 



Garpinus. 



V A closed bladder-like sac ; staminate aments in winter naked Ostrya. 



.a- Nutlet more or less winged, in the axils of persistent scales and without involucre ; 

 staminate flowers 3-6 together in the axils of the scales of the aments and with calyx ; 

 bracts of the fruiting aments 

 b Three-lobed, thin and deciduous ; stamens 2 with 2-branched filaments ; winter buds 



covered with scales Betula. 



b' Erose or 5-lobed, thickened, woody and persistent ; wings of nutlet more or less reduced ; 

 winter buds naked . . . . ; Alnus. 



THE HOENBEAMS. Genus CARPINUS L. 



Trees of about a dozen species with smooth gray Beech-like bark, furrowed and ridged 

 trunks, and confined to the northern hemisphere, but only one is found native in North 

 America. The following are the generic characters : 



Leaves ovate, acute or acuminate, with nearly straight prominent veins. FJov^ers in 

 April ; staminate aments pendulous and with prominent nearly sessile broad ovate acute 

 scales, in the axils of which are found the naked flowers consisting of several stamens with 

 short slender two-branched filaments, each branch bearing a 1-ceIled half-anther hairy at 

 apex ; pistillate aments slender, few-flowered and terminal on leafy branchlets of the year, 

 'with small deciduous scales, each subtended b.v a pair of flowers which are furnished each 

 yvith a small acute bract and pair of bractlets ; calyx adnate to the ovary; stigmas 2. subulate. 

 F'riiit a small compressed ovoid prominently ribbed nut. tipped with calyx-lobes and attached 

 at its base until maturity to a large foliaceous ,3-lobed pale-green involucre formed from the 

 enlarged bract and bractlets of the flower. 



Carpinus is the ancient Latin name of the European Hornbeam. 



For species see pp. llJf-115. 



