Page:Popular Science Monthly Volume 30.djvu/621

Rh Arctic Circle to a mere dwarf; and it is the dwarf form whose leaves occur among the glacial débris of the Norfolk clay-bed. Side by side with it we find the scanty remains of a stunted northern willow (Salix polaris), another of the numerous pygmy shapes which the polymorphous willow type knows so well how to take on under fitting circumstances. It is hard, indeed, to conceive how anybody could ever have watched the gradual stunting of the trees and shrubs, as we ascend a mountain, or approach the Arctic Circle, and yet believe in the separate and deliberate creation of dwarf forms for such great altitudes or high latitudes, like the Mount Washington willows or the polar birch. If we trace the gradual degeneracy of the temperate birchen type, represented by the beautiful American silver or paper birches, through your own shrubby Betula purinla of the Northern bogs, and your petty Betula glandulosa of the high mountains, to the insignificant Betula nana of the arctic regions and of glacial times, it is impossible not to recognize in the entire series one long degradation of a primitive form. Similarly in the willows: every intermediate step may easily be identified, from the large and handsome weeping-willows, through shrubby forms like Salix Lapponum, Salix refens, and Salix myrsinites, till we reach at last the final term in the tiny Salix herbacea of the White Mountains. All are species degraded from a tall and vigorous ancestral tree by the harsh conditions which prevailed at the coming in of the Glacial Epoch.

The shrubs, of course, have fared no better than the forest-trees; but, like the forest-trees themselves, and the lowly herbs, they have learned to accommodate themselves to the situation. Thus the bramble kind, after growing down from the high blackberry and the black raspberry to the level of the trailing dewberry (Rubus Canadensis) and the dwarf raspberry (Rubus trifloms), reaches at last an almost herbaceous type in our British Rubus saxatilis, and finally ends in a mere herb, no bigger than a strawberry-vine, in the true cloudberry of the arctic regions and the New Hampshire hills. So, too, the cornels, starting with your glorious flowering dogwood (Cornus florida), which alone is worth a visit across the Atlantic to see, ends at last in the pretty little bunchberry (C.canadensis) that carpets the woodlands of the high North. And so, once more, the heath family, starting from the noble rhododendron and mountain laurels that glorify and brighten your American hills, tails off at last into the low, spreading, and tufted bog-bilberry, confined entirely to Alpine tops on both sides of the water, and to the mountain bearberry, whose low mats cover the interstices of the rocks among the White Mountains and the higher Maine hills. Everywhere the habit of all these sub-Arctic and glacial plants is just the same, whether their ancestors started in life as trees, or shrubs, or bushes, or herbs; the Alpine azalea is as low and as tufted as the crowberry that mimics it; the Labrador tea is as tiny and as inconspicuous as the Greenland sandwort. On all of them