BETULACE 129 
2, ALNUS, L. 
Stamens 4; scales of female catkin persistent, woody. 
A. glutinosa, Gaertn., our common Alder; also grown 
largely for making charcoal for gunpowder. A. vzrzdczs, 
DC.; leaves ovate, acute, doubly serrate, green on both 
sides, fruit broadly winged ; frequent at a high elevation. 
A. incana, Willd.; leaves glaucous or downy beneath, 
fruit not winged; sides of streams; Switzerland, Jura, 
Lombardy. A. corylifolia, Kern.; leaves roundish-ovate, 
nearly uniformly serrulate, covered with short hairs be- 
neath; Tirol, rare (Pusterthal, Scheiblingstein). 
Order LXXXIII.—SALICACE:. 
Flowers unisexual, dicecious; male and female flowers 
in catkins; calyx 0; stamens 2 or more; ovary I-celled; 
styles 2; ovulesnumerous. Trees and shrubs, belonging 
chiefly to the Northern Temperate and Arctic Zones. 
Ee PORuLts, i: 
Catkins drooping, scales lobed or cut, crenate; stamens 
4-30. Lofty trees; not alpine. 
P. alba, L., White Poplar; leaves cottony beneath; 
occasional. P. nzgra, L., Black Poplar; more common, 
especially by water. . canescens, Sw.; possibly a 
hybrid; occasional. PP. tremula, L., Aspen; common. 
a URSA Pa.) BS! 
Catkins usually erect; scales entire; stamens usually 
2-3. Small trees or shrubs. 
VOL. II. I 
