280 THE FLORA. 
e Involucre a closed, inflated sac, one-flowered, many together in the pendu- 
lous, hop-like cluster. Small trees, with very compact, strong timber, ealled 
Hop Hornbeam. Lron-wood, Lever-wood. Os’TRYA. 
¢ Involucre an open, 8-lobed leaf, 1-flowered, Small trees, with a strong, 
heavy timber. Hornbeam. Carvi’/Nus. 
Orper COXX. BETULACEA. The Birchworts. 
Trees or shrubs, with deciduous stipules, with the alternate 
leaves simple, having the veinlets running straight to the margin; 
Jlowers moneecious, both kinds contained in scaly 
catkins, 2 or 8 under each bract ; calyx and corolla hardly any; 
ovary 2-celled and 2-ovuled, but becoming in 
Jruit a 1-celled and 1-seeded nut, by the suppression of the other seed 
and cell. 
Analysis of the Genera. 
é bracts with 12stam. each; ¢ bracts with mostly 3ovaries. Birch. But’una. 1 
¢ bracts with 4-8 stam. each; Q bracts with 2 ova.or fls. each. Alder, Aunus, 
BET’ULA. Birch, 
é in a cylindrical cat- 
kin, bracts each with 3 
tetrandrous flowers be- 
neath it. ¢ in an oblong 
or egg-shaped catkin, 
bracts 8 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, Fig. 632. Sweet Black Birch (Betula 
doubly serrate lenvea 2.3 lenta), with staminate and _pistillate 
fw owl 
7 tkins: a, a scale with staminate 
with white bark -stallk Eee : 
§ Trees Mat and long: stalked, long flowers ; 0, with pistillate flowers. /ig. 
pointed leaves....4, 5 
: 683, a, A winged samara cut length- 
i i q ; ; Ee 
§ Shrubs with brownish bark, and roundish, wise, showing its fertile and abortive 
erenate leaves....6, 7 cell; b, the sume cut across, 
