BETULACEAE 345 



1. Corylus rostrata Ait. A low shrub 1-2 m. tall, with sparingly pubescent or 

 glabrate twigs. Stems erect, much branched : leaf-blades thinnish, oval or oblong, tend- 

 ing to ovate or obovate, 4-12 cm. long, acute or acuminate, coarsely-serrate, and sharply 

 serrulate, rounded or cordate at the base, slightly inequilateral, glabrous above, paler and 

 sparingly pubescent beneath on the nerves or glabrate ; petioles 4-15 nun. long : staminate 

 aments drooping, 2-5 cm. long, their bracts rhomboidal-obovate, apiculate, ciliate :_ pistil- 

 late aments few-flowered ; bractlets developing a long-beaked tubular involucre, which in- 

 cludes the nut in its base: nut ovoid, 1-1.5 cm. long, flattened, longitudinally riljbed, 

 usually exceeded twice by the slender beak of the involucre. 



In thickets and open woods. Nova Scotia to South Dakota, Georgia and Kansas. Spring. 



2. Corylus Americana Walt. A shrub 1-3 m. tall, with pubescent twigs. Stems 

 erect, often much branched : leaf-blades oval or suborbicular, tending towards ovate or ob- 

 ovate, 5-15 cm. long, acute or short-acuminate, usually undulately-toothed^ and serrulate, 

 rounded or cordate at the base, dark-green and glabrous above, paler and finely pubescent 

 beneath ; petioles 5-10 mm. long : staminate aments drooping, 6-10 cm. long ; bracts broadly 

 oval or nearly so, 3 mm. long, acuminate, the acuminate tips colored : pistillate aments 

 densely few-flowered, their bractlets lobed at the apex, the lobes toothed : nut broadly ovoid, 

 about 1.5 cm. long, somewhat flattened, subtended by the accrescent, laciniate bractlets. 



On hillsides and in thickets, Maine to Manitoba, Georgia and Kansas. Spring. 



Family 2. BETULACEAE Agarclh. Birch Family. 



Monoecious trees or shrubs, with a compact wood, and an aromatic, resinous 

 or astringent, smooth or shining bark which often separates into thin plates. 

 Leaves alternate, deciduous : blades simple, with straight prominent parallel 

 lateral nerves and 2 or several series of often sharp teeth. Staminate aments 

 usually long and drooping with each bract subtending 2-3 flowers : calyx pres- 

 ent : filaments sometimes simple : anther-sacs sometimes contiguous. Pistillate 

 aments seldom drooping, their bracts thickened and woody : calyx wanting. 

 Pistils usually 2-3 at the base of each bract : styles slender. Ovule pendu- 

 lous, anatropous. Fruit a cone-like aggregate of the accrescent bracts, each of 

 which subtends a nut. Seed solitary : testa membranous. 



Stamens 2 : bracts of the mature pistillate aments membranous, 3-lobed, deciduous with the nuts. 



1. Betula. 

 Stamens 4 (3-6) : bracts of the mature pistillate aments thickened and woody, persistent. 2. Alnus. 



1. BETULA L. 



Shrubs or trees, with a resinous aromatic bark, and slender terete branchlets with trans- 

 verse lenticels. Staminate aments elongated, pendulous. Calyx membranous, irregularly 

 4-Iobed, or 2-lobed. Stamens 2, inserted at the base of the calyx : filaments very short, 

 branched at the apex : anther-sacs separated. Pistillate aments erect, oblong or cylindric. 

 dense : bracts elongated, 3-lobed, 3-flowered, accrescent, deciduous. Ovary naked, 2-celled, 

 Nut minute, flattened, the outer coat thin, membranous, and produced into a wing, the 

 inner crustaceous. Seed solitary, pendulous. The plants flower in the spring. Birch. 



Fruiting aments peduncled. 1- B. nigra. 



Fruiting aments sessile at the ends of short branchlets. 



Bark brown : leaf-blades shining above : mature bracts with 2 short divergent lateral 



lobes : nut with triangular-obovate wings. 2. B. lenta. 



Bark yellowish or silvery : leaf-blades dull above : mature bracts with 2 ascending 



lateral lobes : nut with orbicular-obovate wings. 3. B. lutca. 



1. Betula nigra L. A tree, reaching a maximum height of 30 m. and a trunk diameter 

 of 1.5 m. Trunk comparatively slender, its bark varying from brown at the base to a lus- 

 trous silvery or yellow above : leaves not aromatic ; blades rhombic-ovate, 3-6 cm. 

 long, acute, finely "serrate or cut into coarse teeth (the teeth serrate), abruptly narrowed 

 into an entire, broadly cuneate base, glabrous or nearly so above, somewhat tomentose or 

 pubescent on the nerves beneath; petioles pubescent, 0.5-2 cm. long: staminate aments 

 6-8 cm. long ; bracts suborbicular, cuneate at the base, often apiculate at the apex, 2 mm. 

 long, the bractlets rather reniform, erose : pistillate aments nearly 2 cm. long, accrescent 

 into cylindric cones 3-4 cm. long ; bracts pubescent, 3-cleft, the lateral lobes about aslong 

 as the terminal one : nuts ovoid, 3.5 mm. long, flattened, pilose at the apex, furnished 

 with ciliate wings, which form a nearly reniform fruit twice as broad as long. 



On banks of streams and in swamps, Massachusetts to Minnesota and Kansas, Florida and Texas. 

 River Birch. Red Birch. 



