280 



THE FLORA. 



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

 lous, hop-like cluster. Small trees, Avith very compact, strong timber, called 



Ho^p Hornbeam. Iron-wood. Lever-wood. Os'trya, 



c Involucre an open, 3-lobed leaf, 1-flowered, Small trees, with a strong, 



heavy timber. Hornbeam. Carpi'nus. 



Order CXX. BETULACE^. The Birchworts. 



Trees or shrubs.^ -witL 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 3 under each bract ; calyx and corolla hardly any ; 

 ovary 2-celled and 2-ovuled, but becoming in 



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

 and cell. 



Analysis of the Genera. 

 $ bracts with 12 stara. each ; 5 bracts with mostly 3 ovaries. Birch. Bet'ula. 1 

 f bracts with 4-8 stam. each ; $ bracts with 2 ova. or fls, each. Alder. Alnus. 



BET'ULA. Birch. 

 5 in a cylindrical cat- 

 kin, bracts each with 3 

 tetrandrous flowers be- 

 neath it. $ in an oblong 

 or egg - shaped catkin, 

 bracts 3-lobed, each with 3 

 ries or flowers, with no calyx, 

 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 



S Shrubs with brownish bark, and roundish, 

 crenate leaves.... 6, 7 



633 



2-styled ova- 

 Samara 



I'ig. 632. Sweet Black Birch {Betula 

 lenta), with staininate and pistillate 

 catkins : a, a scale with staminate 

 flowers ; h, with pistillate flowers. Fig. 

 633. «, A winged sauiaia cut length- 

 wise, showing its fertile and abortive 

 cell ; h, the same cat across. 



