IIaA'DKOOK of TkKKS of TllK JSOKTUKKX StATKS AM) C'aXADA. 427 



b' Bi-oad-ovate, t-ordato al liasc. i)al(' or rusty bcucatli P. candicans. 



It* Ovate, pale or rusty hcufnth. rounded or \vi<l(' cuiifuir at base, finely cicnate-serrate, 



acuminate !*• balsamifera. 



V Heart-shaped, large, abrupt at apex, creuate-serrate and petioles slijclitly if at all 



flattened P. heterophylla. 



a,= Buds not resin-coated ; leaves orbicular-ovate ; petioles long and 

 b Flattened laterally {Asjxiis) and edges of leaves 



Finely crenato-serrate ; buds glabrous P. treiuiiloides. 



Coarsely dentate; buds scurfy-pubescent P. grandidentata. 



b- Slightly if at all flattened: leaves densely white-tomentose beneath. P. alba. 



Fur .siicoics see pp. 97-113 and the folloiciiif/: 



Ki'ROi'KAN Black I'oplak, /'. nicjra L. A large wide-spreading European tree and nearly 

 n century ago was reported (as /'. II udsonica Michx. and /'. hctiiUfoHa I'ursh. I as naturalized 

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

 typical /*. iiifi'ni. and ai-e equally applicable to the Loml)ardy Poplar (var. Italira) exce])t as 

 noted in the consideration of that tree. Learcs 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. Floirrrs: 

 staminate aments \y.,-l^ in. becoming longer; stamens about 20: pistillate aments '2-'.] in. long, 

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



BIRCH FAMILY. BETULACE^. 



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



properties and grouped in j;ix genera of which five are found in North America. They liave 



the following characters in common : 



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

 stipules fugacious; branchlets terete. Floicers in early spring before or with the unfolding of 

 the leaves, monoecious ; 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-celled extrorse anthers 

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

 with or without calyx, with 2-celled ovary and 2-cleft or bifur( ate style stigmatic at the apex 

 or on the inner surfaces of the branches and a single anatropnus jiendulous ovule in each 

 cell of the ovary. Fruit a small mostly 1-celled 1-seeded luit or samara ; .^eed solitary, 

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



KEY TO THE GENERA. 



.a Nutlet 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 anient and without 

 calyx ; involucre of fruit 

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



Carpinus. 



b" 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-() together in the axils of the scales of the aments and with calyx ; 

 bracts of the fruiting aments 

 b Thi'ee-lobed, thin and deciduous; stamens 2 with 2-branched filaments: winter buds 



covered with scales Betula. 



b- Erose or .")-lobed. thickened, woody and persistent : wings of nutlet more or less reduced ; 

 winter buds nak<'d ' Alniis. 



THE HORNBEAMS. Genus CARPI X US 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: 



JjcarcH ovate, acute or acuminate, with nearly straight prominent veins. Floucrx in 

 April : staminate aments pendulous and with i)rominent 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-celled half-anther hairy at 

 ajiex: pistillate aments slender, few-flowered and terminal on leafy branchlets of the year, 

 with small deciduous scales, each sul)tended by a i)air of flowers which are furnished each 

 with a small acute bract and i)air of bractlets; calyx adnate to the ovary; stigmas 2. subulate. 

 Fruit a small conijjressed ovoid i)rominently ribbed nut. ti))ped with calyx-lobes and attached 

 at its base until maturity to a large foliaceous ."Mobed pali>-green involucre formed from the 

 enlarged bract .nnd bra<tlets of the flower. 



Carpiuus is the ancient Latin name of the European llnrnh.uui. 



For spccicK .sec pp. 11'/ II'). 



