BETULACES. SILVA OF NORTH AMERICA. 
layers. 
The species of Alnus can be easily raised from seeds,! and the varieties propagated by grafts and 
Alnus, the classical name of the Alder, was adopted for this genus by Tournefort” and afterward 
by Linnzus, who subsequently united it with Betula. 
of small woolly cups of brown color on the small branches. The 
aments of Alnus incana are attacked by two curious fungi, Ezo- 
ascus amentorum, Ladebeck, and Erysiphe aggregata, Farlow ; the 1 Cobbett, Woodlands, No. 96. 
former causes some of the scales of the catkins to enlarge so that 2 Inst. 587, t. 359. 
they project an inch or so in the form of more or less twisted club- 
shaped or ligulate masses ; the latter forms a white web over the 
aments, upon which are borne the small black sporangia. 
CONSPECTUS OF THE NORTH AMERICAN ARBORESCENT SPECIES. 
ALNUs. 
Flowers opening in early spring before the unfolding of the leaves from aments formed the 
previous year. 
Stamens, 4. 
Leaves ovate or elliptical, rusty-pubescent on the lower surface . 
Leaves oblong-ovate, glabrous or puberulous on the lower surface . 
Stamens, usually 2 or 3. 
Leaves ovate or oval, pale and slightly puberulous on the lower surface 
Leaves oblong-lanceolate, acute, pale and sometimes puberulous on the lower surface . 
Flowers opening in autumn from aments of the year. 
Leaves oblong, ovate or obovate, dark green and lustrous above, pale yellow-green 
below . 
1. Atnus OREGONA. 
2. ALNUS TENUIFOLIA. 
3. ALNUS RHOMBIFOLIA. 
4. ALNUS ACUMINATA. 
5. ALNUS MARITIMA. 
