280 



THE FLORA. 



c Involucre a closed, inflated sac, one-flowered, many together in the pendn- 

 louB, hop-like cluster. Small trees, with very compact, strong timber, called 



Mop Somheam. Irofir-wood. Lever-wood. Os'trta, 



c Involucre an open, 3-lobed leaf, l-flowered, Small trees, with a strong, 

 heavy timber. Hornbeam. Caepi'nos. 



Order CXX. BETTJLACBiE. The Birchworts. 



Trees or shrubs, with, deciduous stipules, with the alternate 

 leaves simple, having the veinlets running straight to the margin; 

 flowers monoecious, both kinds contained in scaly 

 catkins, 2 or 8 under each bract ; calyx and corolla hardly any ; 

 ovary 2-celled and 2-'oTuled, but becoming in 



fruit a 1-celled and 1-seeded nut, by thfe suppression of the other seed 

 and cell. 



Analysis of the Genera. 

 S bracts with 12 stam. each ; ? briaots with mostly 8 ovaries. JBircA, Bet'itla. 1 

 S bracts with 4^8 stam. each ; ? -bracts with 2 ova. or fls. each. Alder. Aldus. 



BET'ULA. Birch. 

 4 in a cylindrical cat- 

 kin, bracts each with 

 tetrandrous flowers be- 

 neath it. S in an oblong 

 or egg - shaped catkin, 

 bracts 3-lobed, each with 3 2-styled ova- 

 ries or flowers, with no calyx. Samara 

 flattened, broadly winged. — Trees and 

 shrubs, mostly with' the outer bark in thin 

 layers with horizontal fibres. Catkins ap- 

 pearing in early spring before the leaves. 



§ Trees with a yellowish bark, and heart-ovate, 

 serrate leaves 1 



§ Trees with reddish-brown bark, and ovate, 

 doubly serrate leaves 2, 3 



§ Trees with white bark and long-stalked, long- 

 pointed leaves 4, 5 



§ Shrubs with brownish bark, and roundish, 

 crenate leaves .... 6, 7 



Mg. 632. ^weet Black Birch (Betula 

 lenia), with staminate and pistillate 

 catkins : a, a scale with staminate 

 flowers; 6, with pistillate flowers. Mg. 

 683. a, A winged samara cut length- 

 wise, showing its fertile and abortive 

 cell ; &, the same cat across. 



