18431882] GLACIAL PERIOD 443 



" rile " l you, as you say it does, that on p. 73 of my second Letter 338 

 article : for if it troubles you it is not likely to be sound. Of 

 course I had no idea of laying any great stress upon the fact 

 (at first view so unexpected to me) that one-third of our 

 alpine species common to Europe do not reach the Arctic 

 circle ; but the remark which I put down was an off-hand 

 inference from what you geologists seem to have settled viz., 

 that the northern regions must have been a deal cooler than 

 they are now the northern limit of vegetation therefore 

 much lower than now about the epoch when it would seem 

 probable that the existing species of our plants were created. 

 At any rate, during the Glacial period there could have been 

 no phaenogamous plants on our continent anywhere near the 

 polar regions ; and it seems a good rule to look in the first 

 place for the cause or reason of what now is, in that which 

 immediately preceded. I don't see that Greenland could 

 help us much, but if there was any interchange of species 

 between N. America and N. Europe in those times, was not 

 the communication more likely to be in lower latitudes than 

 over the pole ? 



If, however, you say as you may have very good reasons 

 for saying that the existing species got their present diffusion 

 before the Glacial epoch, I should have no answer. I suppose 

 you must needs assume very great antiquity for species of 

 plants in order to account for their present dispersion, so long 

 as we cling as one cannot but do to the idea of the single 

 birthplace of species. 



I am curious to see whether, as you suggest, there would 

 be found a harmony or close similarity between the geogra- 

 phical range in this country of the species common to Europe 

 and those strictly representative or strictly congeneric with 

 European species. If I get a little time I will look up the 

 facts : though, as Dr. Hooker rightly tells me, I have no 

 business to be running after side game of any sort, while 

 there is so much I have to do much more than I shall ever 

 do probably to finish undertakings I have long ago begun. 



1 " One of your conclusions makes me groan, viz., that the line of 

 connection of the strictly alpine plants is through Greenland. I should 

 extremely like to see your reasons published in detail, for it ' riles ' me 

 (this is a proper expression, is it not?) dreadfully" (Darwin to Gray, 

 Jan. ist, 1857, Life and Letters, II. p. 89). 



