a chapter to the New Zealand flora in order to see how far the geological and physical relations between New Zealand and Australia would throw light on its origin, I went for my facts to the works of Sir Joseph Hooker and Mr. Bentham, and also to your article in the “Encyclopaedia Britannica,” and worked out my conclusions solely from these, and from the few facts referring to the migration of plants which I had collected.  Had I referred again to your lecture I should certainly have quoted the cases you give (in a note, p. 431) of plants extending along the Andes from California to Peru and Chile, and vice versa.  Whatever identity there is in our views was therefore arrived at independently, and it was an oversight on my part not referring to your views, partly due to your not having made them a more prominent feature of your very interesting and instructive lecture.  Working as I do at home, I am obliged to get my facts from the few books I can get together; and I only attempted to deal with these great botanical questions because the facts seemed sufficiently broad and definite not to be much affected by errors of detail or recent additions to our knowledge, and because the view which I took of the past changes in Australia and New Zealand seemed calculated to throw so much light upon them.  Without such splendid summaries of the relations of the Southern floras as are given in Sir J. Hooker’s Introductions, I should not have touched the subject at all; and I venture to hope that you or some of your colleagues will give us other such summaries, brought down to the present date, of other important floras—­as, for example, those of South Africa and South Temperate America.

Many thanks for additional peculiar British plants.  When I hear what Mr. Mitten has to say about the mosses, etc., I should like to send a corrected list to Nature, which I shall ask you to be so good as to give a final look over.—­Believe me yours very faithfully,

ALFRED R. WALLACE.

P.S.—­Mr. Darwin strongly objects to my view of the migration of plants along mountain-ranges, rather than along lowlands during cold periods.  This latter view seems to me as difficult and inadequate as mine does to him.—­A.R.W.

* * * * *

Wallace was in frequent correspondence with Professor Raphael Meldola, the eminent chemist, a friend both of Darwin and of Wallace, a student of Evolution, and a stout defender of Darwinism.  I received from him much help and advice in connection with this work, and had he lived until its completion—­he died, suddenly, in 1914—­my indebtedness to him would have been even greater.

The following letter to Meldola refers to a suggestion that the white colour of the undersides of animals might have been developed by selection through the physical advantage gained from the protection of the vital parts by a lighter colour and therefore by a surface of less radiative activity.  The idea was that there would be less loss of animal heat through such a white coating.  We were at that time unaware of Thayer’s demonstration of the value of such colouring for the purposes of concealment among environment.  Wallace accepted Thayer’s view at once when it was subsequently put forward; as do most naturalists at the present time.