66 KEY AND FLORA 



1. C. caroliniana Walt. Hornbeam. A small tree with smooth 

 and close gray bark; twigs slender. Leaves ovate-oblong, acute or 

 taper-pointed, sharply and doubly serrate, the straight veins termi- 

 nating in the larger serrations ; downy when young and soon be- 

 coming smooth. Staminate catkins l-li in. long. Pistillate catkins 

 long-peduncled, 8-12-flowered ; bractlets becoming nearly 1 in. long, 

 cut-toothed, the middle tooth much longer than the others. In rich, 

 moist woods. Often known as "blue beech " and "ironwood."* 



IV. BETULA L. 



Trees with slender, aromatic twigs, and thin, usually straight- 

 veined leaves. Staminate catkins drooping, flowers usually 3 

 in the axil of each bract ; stamens 4, short ; anthers 1-celled. 

 Pistillate catkins erect, flowers 2 or 3 in the axil of each bract ; 

 ovary sessile, 2-celled ; styles 2 ; bracts 3-lobed ; perianth none. 

 Nut broadly winged.* 



1. B. lenta L. Cherry Birch. Leaves ovate or oblong-ovate, 

 acute, heart-shaped, finely and doubly serrate, silky when young ; 

 petioles about h in. long. Staminate catkins clustered, 3-4 in. long. 

 Pistillate catkins sessile, about 1 in. long ; cylindrical bracts spread- 

 ing, acute, smooth. River banks, especially N. A large tree, with 

 aromatic twigs. The oil contained in the bark and twigs is distilled 

 and used as a substitute for wintergreen.* 



2. B. lutea Michx. f. Yellow Birch. A large forest tree, some- 

 times 60-90 ft. high, with yellowish or silver-gray bark, which peels 

 off in extremely thin layers. Leaves ovate or nearly so, usually taper- 

 pointed, rounded or sometimes almost heart-shaped at the base, 

 sharply and finely serrate, somewhat downy on the veins beneath. 

 3-5 in. long. Staminate catkins 3-3| in. long; pistillate catkins 

 about I in. long. Rich woods N., also southward in the mountains. 



3. B. nigra L. River Birch, Red Birch. A medium-sized tree 

 with reddish-brown bark. Leaves rhombic-ovate, acute at the apex, 

 acute or obtuse at the base, sharply and doubly serrate, white-downy 

 below, becoming smoother with age, petioles short. Staminate catkins 

 2-3 in. long. Pistillate catkins 1-1| in. long, peduncles short, bracts 

 nearly equally 3 -cleft, woolly. River banks, especially S. and W.* 



4. B. populifolia Marsh. Gray Birch. A tall shrub or slender, 

 straggling tree, 15-30 ft. high, seldom growing erect, often several 

 trunks springing from the ground almost in contact and slanting 

 away from each other. Leaves triangular, with a long taper point 

 and truncate base, unevenly twice serrate, with rather long, slender 

 petioles, which allow the leaves to quiver like those of the aspen. 



