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, January 1st, 1857, "Life and Letters," II., page 89).) you, as you say it does,--that on page 73 of my second 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 geographical range in this country of the species common to Europe and those strictly representative or strictly congeneric with European species.