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The Chairman (Professor Weiss) then read a letter from Dr. Alfred Russel Wallace, F.R.S., to Mr. Clement Reid, in which the following passages occur: 'I have read your paper on British plants and the Glacial Period with great interest, mainly because you support my views of the great powers of distribution of plants over the ocean, not only for a few tens of miles, but for many hundreds and even, in rare cases, thousands. I really wish you would look up and read again my discussion of the Flora of the Azores, in my "Island Life." In this case there is absolutely no doubt that the whole of its plants have been gradually introduced during the latter half of the Tertiary Period over a width of ocean of about a thousand miles by such causes as you mention, while the absence of all those genera whose seed could not have passed by those means, completes the proof. . . . But while, therefore, I quite agree with your argument as to the fact of the very large number of our species which have been so derived since the Glacial Period, I cannot accept your view that the whole has been so introduced, for several reasons. It is certain that temperature is only one of many, very many, factors that determine the distribution of species; and it is also certain that at the

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southern limit of the ice-sheet the winter temperature may have been quite mild enough to support a large number of our species. In a large part of the South of England I see no reason why hundreds of species may not have lived since the pliocene, the covering of snow during the winter being a compensation for the lower temperature of the air for a portion of the time. . .'