S8 WAYSIDE AND WOODLAND TREES. 
The leaf-stalks of the Aspen are longer than those of its 
congeners, so that they are constantly on the flutter — a cir- 
cumstance that has led to an explanatory legend, to the 
effect that the cross of Calvary was made of Aspen-wood, and 
that the tree shivers perpetually in remembrance. Possibly 
the present inferiority of Aspen timber is to be explained in a 
similar manner. The catkins, which are two or three inches 
long, are similar to those of the foregoing species, but the 
scales have jagged edges. It is indigenous in all the British 
Islands as far north as Orkney, but, though commonly found 
in copses on a moist light soil, is more frequent as a planted 
tree in gardens and pleasure grounds. It is a characteristic 
tree of the plains throughout the Continent, but ascends to 
1600 feet in Yorkshire, and in the Bavarian Alps is found 
as high as 4400 feet. It is not a deep-rooting tree, the root- 
branches running almost horizontally. Where accessible to 
cattle or deer, the foliage of the suckers is eagerly browsed by 
them. 
The Black Poplar {Populus nigra) appears to be so called 
not by reason of any blackness of leaf or bark, but because of 
the absence of any white or grey down on the underside of 
its leaves. Its bark is grey, like that of the species already 
mentioned, but readily distinguished from them by the great 
swellings and nodosities that mar the symmetry of its trunk. 
It is a tree of erect growth, fifty to sixty feet in height, with 
horizontal branches, and leaves that vary in shape from 
triangular and rhombic to almost circular, and in width from 
an inch to four inches. They have rounded teeth on the 
margins, which are at first also fringed, and in their young 
state the underside is silky. The flowers in the catkins of 
this and the next species are not so densely packed. Those oi 
the male are two or three inches in length, and dark red in 
colour ; their abundance before the tree has put out its leaves 
makes the male tree a conspicuous object. The female catkins 
