DISTRIBUTION OF ARCTIC PLANTS. 125 



Arctic-European species, which are all likewise American 

 plants, but are remarkable for their absence from Greenland, 

 would indicate no small difficulty in the westward migration, 

 and render it most probable that the diffusion of species from 

 the Old World to the New was eastward through Asia, for 

 the arctic no less than (as has elsewhere been shown) for the 

 temperate plants. AY as it that Greenland and the adjacent 

 part of the American continent remained glacial longer than 

 the rest of the zone ? And if our northern regions were thus 

 colonized by an ancient Scandinavian flora, this seems to 

 have been in return for a still earlier donation of American 

 plants to Europe, to which a very few existing but numerous 

 fossil remains bear testimony. Speculative inquiries of this 

 sort are enticing, and the time is approaching in which they 

 may be fruitful. 



Indeed, the characteristic features and the immediate in- 

 terest and importance of the present memoir, as of others 

 of the same general scope and interest, are found in this : 

 1. That the actual geographical distribution of species is 

 something to be accounted for ; 2. That our existing species, 

 or their originals, are far more ancient than was formerly 

 thought, mainly if not wholly antedating the glacial period ; 

 and, 3- That they have therefore been subject to grave climatic 

 vicissitudes and changes. There may be many naturalists 

 who still hesitate to accept these propositions, as there are 

 one or two who deny them ; but these or similar conclusions 

 have evidently been reached by those botanists, paleontolo- 

 gists, and geologists in general who have most turned their 

 thoughts to such inquiries, and who march foremost in the 

 advancing movement of these sciences. In this position, the 

 author of the present memoir, — prepossessed with Darwin's 

 theory of the diversification of species through natural selec- 

 tion, — having occasion to revise systematically the materials 

 of the arctic flora, is naturally led to compare the new theory 

 with the facts of the case in this regard ; to see how far the 

 vicissitudes to which it is all but demonstrated that the plants 

 of the northern hemisphere have long been subjected, and 

 the modifications and extinctions which he thinks must have 



