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