418 Salictnee—Populus. 
are confined to the northern hemisphere. The generic name 
is of classical origin. 
1. P. trémula. Aspen.—An indigenous tree with glabrous 
buds, pubescent shoots, orbicular-cordate entire or angularly 
toothed leaves glabrous or pubescent beneath, on long slender 
laterally compressed petioles. Scales of the rather small catkins 
ciliate and deeply cut. Stamens about 8. This tree rarely 
exceeds 50 fect in height, and is remarkable for the almost 
perpetual quivering motion of the leaves. There is a good 
weeping variety. 
P. tremuloides, the American Aspen, is an allied species 
with roundish-cordate sharp-pointed minutely regularly-toothed 
leaves. P. Gries, a slight variety of the foregoing, or perhaps 
the selfsame thing, is represented in gardens by a weeping form. 
2. P. alba, syn. P. nivea, ete. Abele.—A large fast-growing 
tree with glabrous buds, pubescent shoots, ovate-cordate or del- 
toid lobed and toothed leaves densely clothed with a cottony 
down on the lower surface, and long slender petioles. Scales 
of the catkins ciliate. This is very rare in a wild state, and 
perhaps not truly indigenous. P. canéscens, the Grey Poplar, 
is a varicty with smaller rarely lobed leaves having a greyish 
tomentum. 
3. P.unigra. Black Poplar.—-A fast-growing spreading tree 
from 50 to 80 feet high with vlabrons shoots and glutinous 
buds. Leaves triangular-ovate, acuminate, serrate, rounded 
at the base, silky beneath when young; petiole slender, com- 
pressed. A native of Europe and North Asia, now much 
planted in this country. There is a narrow-leaved variety 
called salicifolia. 
4. P.pyramidalis, syn. P. fastigiata, and P. dilatata, Tom- 
bardy Poplar.—This is very distinct in habit, and easily recog- 
nised from all other Poplars by its slender erect branches ; but 
it is nevertheless considered to be a form of the same species as 
the last. In aspect it is distinct from all other deciduous trees, 
approaching the close perpendicular growth of the Cypresses. 
It attains a height of 100 to 150 feet, and is found wild in 
Southern Europe and the Himalaya mountains. 
5. P. balsamiferu. Balsam Poplar, Tacamahac.—This is the 
most commonly planted of the North American species, and 
resembles P. nigru in foliage, but the branches are round, 
not angular, and the bark more furrowed. The leaves too 
are quite glabrous, strictly ovate-acuminate, with a rounded 
