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. TO PROF. MELDOLA _Frith Hill, Godalming. April 8, 1885._ My dear Meldola,--Your letter in _Nature_ last week "riz my dander," as the Yankees say, and, for once in a way, we find ourselves deadly enemies prepared for mortal combat, armed with steel (pens) and prepared to shed any amount of our own--ink. Consequently I rushed into the fray with a letter to _Nature_ intended to show that you are as wrong (as wicked) as are the Russians in Afghanistan. Having, however, the most perfect confidence that the battle will soon be over,... --Yours very faithfully, ALFRED R. WALLACE. * * * * * The following letter refers to the theory of physiological selection which had recently been propounded by Romanes, and which Prof. Meldola had criticised in _Nature_, xxxix. 384. TO PROF. MELDOLA _Frith Hill, Godalming. August 28, 1886._