the islands in the
North Atlantic, for example.

(b) The temporary occupation of mountain stations by migrating plants
(which I think I have shown to be probable) renders _time_ a much more
important element in increasing the number and variety of the plants so
dispersed than in the case of islands, where the flora soon acquires a
fixed and endemic character, and where the number of species is
necessarily limited.

No doubt, direct evidence of seeds being carried great distances through
the air is wanted, but, I am afraid, can hardly be obtained. Yet I feel
the greatest confidence that they _are_ so carried. Take for instance
the two peculiar orchids of the Azores (Habinaria species): what other
mode of transit is conceivable? The whole subject is one of great
difficulty, but I hope my chapter may call attention to a hitherto
neglected factor in the distribution of plants.

Your references to the Mauritius literature are very interesting, and
will be useful to me; and again thanking you for your valuable remarks,
believe me yours very faithfully,

ALFRED R. WALLACE.

* * * * *

_Pen-y-bryn, St. Peter's Road, Croydon. November 21, 1880._

My dear Darwin,--Many thanks for your new book containing your wonderful
series of experiments and observations on the movements of plants. I
have read the introduction and conclusion, which shows me the importance
of the research as indicating the common basis of the infinitely varied
habits and mode of growth of plants. The whole subject becomes thus much
simplified, though the nature of the basic vitality which leads to such
wonderful results remains as mysterious as ever.--Yours very faithfully,

ALFRED R. WALLACE.

* * * * *

_Pen-y-bryn, St. Peter's Road, Croydon. January 1, 1881._

My dear Darwin,--I have been intending to write to you for some weeks to
call your attention to what seems to me a striking confirmation (or at
all events a support) of my views of the land migration of plants from
mountain to mountain. In _Nature_ of Dec. 9th, p. 126, Mr. Baker, of
Kew, describes a number of the alpine plants of Madagascar as being
_identical species_ with some found on the mountains of Abyssinia, the
Cameroons, and other African mountains. Now, if there is one thing more
clear than another it is that Madagascar has been separated from Africa
since the Miocene (probably the early Miocene) epoch. These plants m