332 COTtoLIFEBA (oak family.) 



1. BE TULA, Tonrn. Biech. 



Sterile flowers 3, and bractlets 2, under each shield-shaped scale or bract of 

 the catkins, consisting each of a calyx of one scale bearing 2 two-parted fila- 

 ments. Fertile flowers without bractlets or calyx. — Outer bark usually 

 separable in sheets, that of the branchlets dotted. Twigs and leaves often 

 spicy-aromatic. 



1. B. oecidentalis, Hook. Becoming 10 or 20 feet high, with close dark- 

 colored bark (at length light brown) ; branches more or less resinous-dotted 

 at the extremities : leaves thin, broadly ovate, acute, truncate or rounded or 

 somewhat cuneate at base, with short glandular-tipped serratures and often ob- 

 scurely lobed, somewhat resinous above, smooth or slightly appressed-villous 

 beneath : the divaricately 3-lobed bracts pubescent ciiiate : wings of the nutlet us 

 broad as the body or broader. — From California to Washington and the Sas- 

 katchewan, and in the Rocky Mountains to New Mexico. Sometimes called 

 " Black Birch." 



2. B. glaildulosa, Michx. A low bush, 4 to 6 feet high or less, the dark- 

 colored branches usually more or less resinous-glandular : leaves small, obovate 

 to oblong-obovnte, mostly cuneate at base, rounded and crenate above, smooth 

 and often resinous-coated : the deeply 3-lobed bracts slightly ciiiate : seed orbicu- 

 lar-winged. — From California to Sitka, and eastward through British America 

 to the Atlantic, and southward in the mountains to New Mexico. 



2. ALNUS, Tourn. Aider. 



Sterile flowers 3, and bractlets 4 or 5 under each short-stalked shield-shaped 

 scale, consisting each of a 3 to 5-parted calyx and as many stamens, with the 

 filaments short and simple. Fertile flowers with a. calyx of 4 little scales 

 adherent to the scales or bracts of the catkin. 



§ 1. Flowers developed in spring with the haves; the sterile from cnth'ns which 

 have remained naked over winter ; while the fertile have been enclosed in a 

 scaly bud: fruit with a conspicuous thin wing. 



1. A. viridis, DC. Shrub 3 to 8 feet high: leaves round-oval, ovate, or 

 slightly heart-shaped, glutinous and smooth or softly dowuy underneath, ser- 

 rate with very sharp and closely set teeth, on young shoots often cut-toothed i 

 fertile catkins slender-stalked, clustered, ovoid. — Mountains of Colorado and 

 northward into 3ritish America, and thence eastward to N. New York and 

 New England. 



§ 2. Flowers developed in earliest spring, before the leaves, from mostly clus- 

 tered catkins which {both sorts) were formed the foregoing summer and hare 

 remained naked over winter: fruit wingless or with a narrow coriaceous 

 margin. 



2. A. incana, Willd. Shrub or small tree 8 to 20 feet high : leaves 

 broadly oval or ovate, rounded at the base, sharply serrate, often coarsely 

 toothed, whitened and mostly downy underneath : fruit orbicular. — From 

 Colorado northward and thence eastward. 



Var. vireseens, Watson. Leaves acutely double toothed, light green and 

 glabrous on both sides or sparingly pubescent : nutlets round-obovate, thinly 



