GENERA. 



I. BETULEiE. 



1. Betula T. — Flowers amentaceous monoecious apetalous ; 

 calyx 4-phyllous ; folioles connate at base, very unequal ; one more 

 largely developed; the others smaller squamiform, very small or 

 abortive. Stamens 2 (or 4 ?), central ; filaments (anterior and 

 posterior) 2-fid above ; cells of each anther bence widely separate, 

 extrorsely longitudinally rimose. Female flower naked ; gymecium 

 free. Germen compressed, 2-locular ; style nearly 2-partite at base ; 

 branches elongate filiform, stigmatose above. Ovules in cells 1 (very 

 rarely 2), descending anatropous ; micropyle extrorsely superior. 

 Fruit dry, indéhiscent, angular or samaroidly alate at margin, 

 crowned with style, generally by abortion 1-spermous. Seed de- 

 scending ; coat thin ; cotyledons of exalbuminous embryo, flat, rather 

 fleshy, at germination foliaceous ; radicle superior. — Trees or shrubs ; 

 leaves alternate, penninerved ; stipules lateral, oftener caducous ; 

 male catkins solitary or 2-nate, from aphyllous lateral and terminal 

 buds, generally precocious ; scales of catkin peltate, with internal 

 squamule on each side, 3-florous ; female catkins from lateral 

 3-5-phyllous buds, solitary or more rarely racemose on common 

 peduncle ; scales of catkin subentire or oftener (from adnate lateral 

 scales) 3-lobed, imbricate, 2-3-florous, finally oftener deciduous 

 with fruit; cone oblong or ovoid. (Temp, and cold regions of both 

 worlds in North, hemisphere.) — See p. 220. 



2. Alnus T. — Flowers monoecious (nearly of Betula) ; male calyx 

 oftener subequally or unequally 4-partite, more rarely 10-12-phyllous. 

 Stamens equal in number and opposite sepals ; anthers 2-locular. 



VOL. vi. 17 



