The Grey Poplar (Populus canescens), which is thought to be indigenous only in the south-eastern parts of England, is not so tall a tree as P. alba, though it sometimes attains to eighty or ninety feet, with a circumference between ten and twenty-four feet. Its life extends to about a century, but its wood—which does not split when nails are driven through thin boards of it—is considered best between fifty and sixty years of age. The leaves on the branches are shaped like those of P. alba, but their under sides are either coated with grey down or are quite smooth; those of the suckers have their margins cut into angles and teeth. The female flowers mostly have four wedge-shaped purple stigmas (sometimes two), which are cleft into four at their extremities.
The Aspen or Asp (Populus tremula) does not attain either
to so large a size or so moderate an age as the Abele. Its height, when full grown, is from forty to eighty feet, and after fifty or sixty years its heart-wood begins to decay, and its destruction is then hastened by the attacks of such internal-feeding insects as the caterpillars of the Goat-moth and the Wood Leopard-moth. The leaves on the branches are broadly egg-shaped, approaching to round, the waved margin cut into teeth with turned-in points. In one form (var. villosa) the leaves are covered beneath with silky or cottony hairs; in the other form (var. glabra) they are almost smooth. The leaves on the suckers are heart-shaped, without teeth.
The leaf-stalks of the Aspen are longer than those of its congeners, so that they are constantly on the flutter—a circumstance 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.