454 OUR WOODLAND TREES. 
especial subject of this chapter, attains a height 
varying from fifty to about eighty feet. Its 
specific name of nigra, or black, was probably 
given to it not because of the particular darkness 
of its foliage, but to distinguish it from the whiter- 
foliaged Populus alba. A dark circle, perceptible 
at the centre of its trunk, has, however, been sup- 
posed by some persons to have originated its 
specific name, whilst, according to others, the 
sombre colour of its bark has suggested the 
appellation of nigra. 
The leaf of the present species is readily dis- 
tinguishable from those of the other three by 
its smooth surface, pointed apex, and serrated 
margin. It is, indeed, in shape, what might be 
called roughly triangular, or, more strictly speak- 
ing, four-sided. The venation consists of a mid- 
vein, and of two other principal veins, forking 
from it at the base of the leaf, each giving origin 
to somewhat wavy and forked veinlets proceeding 
towards the serratures in the leaf margin. The 
catkins, which are conspicuous on the Tree before 
the opening of the foliage, are produced in March 
and April. The male catkins are pendant in 
