HOOKER ON ARCTIC PLANTS. 201 



tribution, at which I have now arrived from an examination of 

 the several polar districts, and especially of that of Greenland. 



A glance at the appended chart [not reproduced here] shows 

 how this theory bears upon the Greenland flora, explaining the 

 identity of its existing vegetation with that of Lapland, and ac- 

 counting 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 vegetation southwards, it is evident that the Green- 

 land individuals, from being confined to a peninsula, would be 

 exposed to very diifercnt conditions to those of the great conti- 

 nents. 



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 peninsula ; and not being there 

 brought into competition with other types, there could be no 

 struggle for life amongst their progeny, and, consequently, no 

 selection of better adapted varieties. On the return of heat these 

 survivors would simply travel northwards, unaccompanied by the 

 plants of any other conntry. 



In Arctic 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 sub-species, 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 competi- 

 tion 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 

 Arctic 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-Moun- 

 tain species would accompany them to the Arctic Zone, while 

 many Arctic species would ascend those mountains, accompanying 

 the Alpine species in their re-ascent. 



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 

 Avhich 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 Moun- 

 tains, Potentilla tridentata 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 Avarmth, were ex- 

 terminated on the plains of the American continent, but found 

 a refuge on its mountains, where they now exist. 



It appears, thei-efore, to be no slight confirmation of the 



