254 DR. HOOKER ON THE DISTRIBUTION OF ARCTIC PLANTS. 



A glance at the appended chart shows how this theory bears upon the Greenland flora, 

 explaining the identity of its existing vegetation with that of Lapland, and accounting 

 for its paucity of species, for the rarity of American species, of peculiar species, and of 

 marked varieties of European species. If it be granted that the polar area was once 

 occupied by the Scandinavian flora, and that the cold of the glacial epoch did drive this 

 veo-etation southwards, it is evident that the Greenland individuals, from being confined 

 to a peninsula, would be exposed to very diiferent conditions to those of the great con- 

 tinents. In Greenland many species would, as it were, be driven into the sea, that is, 

 exterminated ; and the survivors would be confined to the southern portion of the penin- 

 sula, and not being there brought into competition with other types, there could be no 

 struo-o-le for life amongst their progeny, and consequently no selection of better-adapted 

 varieties. On the return of heat, these survivors would simply travel northwards, unac- 

 companied by the plants of any other country. 



In Ai'ctic America and Asia, on the other hand, where there was a free southern extension 

 and dilatation of land for the same Scandinavian plants to occupy, these would multiply 

 enormously in individuals, branching off into varieties and subspecies, and occupy a 

 larger area the further south they were driven ; and none need be altogether lost in the 

 southern migration over plains, though many would in the struggle that ensued when 

 they reached the mountains of those continents and were brought into competition with 

 the alpine plants, which the same cold had caused to descend to the plains. Hence, on 

 the return of warmth, many more Scandinavian species would return to Arctic America 

 and Asia than survived in Greenland ; some would be changed in form, because only the 

 favoured varieties could have survived the struggle ; some of the Alpine Siberian and 

 Rocky Mountain species would accompany them to the arctic zone ; while many arctic 

 species would ascend those mountains, accompanying the alpine species in their reascent. 

 Again, as the same species may have been destroyed in most longitudes, or at most 

 elevations, but not at all, we should expect to find some of those Arctic Scandinavian plants 

 of Greenland which have not returned to Arctic America still lurking in remote alpine 

 corners of that great continent ; and we may account for Draba aurea being confined to 

 Greenland and the Rocky Mountains, Fotentilla trldentata to Greenland and Labrador, 

 and Arenaria Grcenlandica to Greenland and the White Mountains of New Hampshire, 

 by supposing that these were originally Scandinavian plants, which on the return of 

 warmth were exterminated on the plains of the American continent, but found a refuge 

 on its mountains, where they now exist. 



It appears, therefore, to be no slight confirmation of the general truth of Mr. 

 Darwin's hypothesis, that, besides harmonizing with the distribution of arctic plants 

 within and beyond the polar zone, it can also be made, without straining, to account for 

 that distribution and for many anomalies of the Greenland flora, viz., 1, its identity with 

 the Lapponian ; 2, its paucity of species ; 3, the fewness of temperate plants in temperate 

 Greenland, and the still fewer plants that area adds to the entire flora of Greenland ; 4, 

 the rarity of both Asiatic and American species or types in Greenland ; and 5, the pre- 

 sence of a few of the rarest Greenland and Scandinavian species in enormously remote 

 alpine localities of West America and the United States. 



