The commoner and less desirable of the two forms has been named _B. pubescens_, owing to the young shoots being clothed with down, sometimes so minute as to require a lens to show it. This and the habit of the tree are the only constant marks of distinction from the other form, which is named _B. verrucosa_, because the shoots, though shining and perfectly free from down, are studded with minute _verrucæ_, or warts, easily discernible by the naked eye. I have found in southern Norway, where the two reputed species grow together, intermediate forms which are no doubt natural hybrids.
The two species are usually quite different in habit, the common birch (_B. pubescens_) never carrying the long pendulous branchlets which distinguish the silver birch (_B. verrucosa_). Moreover, the common birch does not usually attain the stature of the other, although Mr. Elwes mentions having measured one at Malborough 90 feet high, with a girth of 8 feet. This is the species which grows naturally over the greater part of Scotland, especially in the west and north. The distinctive downiness of the young twigs may have had its origin in the humid atmosphere and abundant rainfall of the regions where it most abounds. Geographically it enjoys a very wide range, extending farther north than any other tree--as far as latitude 71° near the North Cape--and reappearing in Iceland and southern Greenland, far within the limit of floating ice. Eastward it extends as far as Kamschatka, but it does not reach southward beyond the Alps, not being found in the Pyrenees or the Apennines, whereas the silver birch reaches down to Sicily.
Coming to the north-east of Scotland, to Strathspey, Deeside, and part of the basin of the Moray Firth, one finds a change in the aspect of the birch forest; for here, although the common birch still prevails on the wetter parts, the silver birch is dominant on the drained land and hill sides. It is there that the lady of the woods displays her true grace and it is hard to say whether she is more lovely in summer, when she waves her long green tresses in the breeze, or in winter, when the slanting sunbeams glint on the snowy stem, and the drooping branchlets appear like fine tracery against the sky. This is the true weeping birch so highly prized by landscape gardeners, and this is the species that should always be chosen for planting, provided the land is well drained, for it cannot stand damp feet with the same impunity as its cousin. The general rule is not difficult to remember that, whereas the common or downy birch will grow on almost any soil that is not actual swamp, the silver or weeping birch is very impatient of stagnant moisture.