1868.] HOOKER — ARCTIC FLORA. 329 



closely allied but more or less distinct varieties or even species, 

 whose geographical limits overlap, and whose members very 

 probably occasionally breed together. 



Nor is the application of this hypothesis limited to this inquiry ; 

 for it offers a possible explanation of a general conclusion at which 

 I had previously arrived * and shall have again to discuss here — 

 viz. : that the Scandinavian flora is present in every latitude of the 

 globe, and is the only one that is so; and it also helps to explain 

 another class of most interesting and anomalous facts in arctic 

 distribution, at which I have now arrived from an examination o^ 

 the vegetation of the several polar districts, and especially that 

 of Greenland. 



A glance at a circumpolar chart will show 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 sj)ecies, 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 south- 

 wards, it is evident that the Greenland individuals, from being 

 confined to a peninsula, would be exposed to very different con- 

 ditions to those of the great continents. 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 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 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 



* Introductory Essay to the ' Flora of Tasmania,' p. ciii. 



