same conditions, become so
like each other that the pollen of one has hardly any more effect on
the others than their own pollen? Or, on the contrary, were the plants
originally one--i.e., are they suckers from a single stock, which
have gained a slight degree of mutual fertility in the course of an
independent life? Or, lastly, is the result 'ein neckische Zufall,'"
(The above is a free translation of Muller's words.)) I am convinced
that if you can prove that a plant growing in a distant place under
different conditions is more effective in fertilisation than one
growing close by, you will make a great step in the essence of sexual
reproduction.

Prof. Asa Gray and Dr. Hooker have been staying here, and, oddly
enough, they knew nothing of your paper on Martha (678/3. F. Muller has
described ("Bot. Zeitung," 1866, page 129) the explosive mechanism by
which the pollen is distributed in Martha (Posoqueria) fragrans. He
also gives an account of the remarkable arrangement for ensuring
cross-fertilisation. See "Forms of Flowers," Edition II., page 131.),
though the former was aware of the curious movements of the stamens, but
so little understood the structure of the plant that he thought it was
probably a dimorphic species. Accordingly, I showed them your drawings
and gave them a little lecture, and they were perfectly charmed with
your account. Hildebrand (678/4. See Letter 206, Volume I.) has repeated
his experiments on potatoes, and so have I, but this summer with no
result.

LETTER 679. TO F. MULLER. Down, March 14th [1869].

I received some time ago a very interesting letter from you with many
facts about Oxalis, and about the non-seeding and spreading of one
species. I may mention that our common O. acetosella varies much
in length of pistils and stamens, so that I at first thought it was
certainly dimorphic, but proved it by experiment not to be so. Boiseria
(679/1. This perhaps refers to Boissiera (Ladizabala).) has after all
seeded well with me when crossed by opposite form, but very sparingly
when self-fertilised. Your case of Faramea astonishes me. (679/2. See
"Forms of Flowers," Edition II., page 129. Faramea is placed among the
dimorphic species.) Are you sure there is no mistake? The difference
in size of flower and wonderful difference in size and structure of
pollen-grains naturally make me rather sceptical. I never fail to admire
and to be surprised at the number of points to which you attend. I go