462 OUR WOODLAND TREES. 
which are not so prominent in the leaves of the 
other species of Poplar. In their general form, 
and in the waviness and general character of the 
indentations on their margins, the leaves of 
Populus tremula resemble those of the Grey Poplar. 
But they are smaller and, usually, rounder; and, 
although they are slightly downy on their under 
sides when they are young, they afterwards 
become smooth on both sides, being of a dark 
shining green on their upper surfaces. Though a 
rapid grower and a large Tree, Tremula does not 
usually attain the size of Alba, rarely exceeding 
fifty feet in height. It has a straight stem, and 
when young—and until it becomes cracked by 
age—smooth bark. Its catkins are cylindrical 
and pendulous, each flower in the male catkins 
containing four erect stigmas. The flowers are 
brown in colour, and the autumnal leaves also 
turn to a dark brown colour, sometimes being 
almost black. Though the Aspen does not quite 
so readily grow from cuttings as the other species 
of Poplar which have been described, it throws 
up from its surface-roots suckers in sufficient 
abundance to admit of extensive culture. 
