25 A 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 
vegetation southwards, it is evident that the Greenland individuals, from being confined 
to a peninsula, would be exposed to very different 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 
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, unac- 
companied by the plants of any other country. 
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 subspecies, and occupy a 
larger area the farther 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 
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 iov Draba aurea being confined to 
Greenland and the Rocky Mountains, JPotentilla 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 
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. 
Danyin'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 
alpme localities of West America and the United States 
