am not at
all afraid of having to alter my views in many points of detail. I was
so overwhelmed with zoological details that I never went through the
Geological Society's _Journal_ as I ought to have done, and as I mean to
do before writing more on the subject.

With best wishes, believe me yours very faithfully,

ALFRED R. WALLACE.

* * * * *

_Rose Hill, Dorking. December 13, 1876._

My dear Darwin,--Many thanks for your new book on "Crossing Plants,"
which I have read with much interest. I hardly expected, however, that
there would have been so many doubtful and exceptional cases. I fancy
that the results would have come out better had you always taken
weights instead of heights; and that would have obviated the objection
that will, I daresay, be made, that _height_ proves nothing, because a
tall plant may be weaker, less bulky and less vigorous than a shorter
one. Of course no one who knows you or who takes a _general_ view of
your results will say this, but I daresay it will be said. I am afraid
this book will not do much or anything to get rid of the one great
objection, that the physiological characteristic of species, the
infertility of hybrids, has not yet been produced. Have you ever tried
experiments with plants (if any can be found) which for several
centuries have been grown under very different conditions, as for
instance potatoes on the high Andes and in Ireland? If any approach to
sterility occurred in mongrels between these it would be a grand step.
The most curious point you have brought out seems to me the slight
superiority of self-fertilisation over fertilisation with another flower
of the same plant, and the most important result, that difference of
constitution is the essence of the benefit of cross-fertilisation. All
you now want is to find the neutral point where the benefit is at its
maximum, any greater difference being prejudicial.

Hoping you may yet demonstrate this, believe me yours very faithfully,

ALFRED R. WALLACE.

* * * * *

_Rose Hill, Dorking. January 17, 1877._

My dear Darwin,--Many thanks for your valuable new edition of the
"Orchids," which I see contains a great deal of new matter of the
greatest interest. I am amazed at your continuous work, but I suppose,
after all these years of it, it is impossible for you to remain idle. I,
on the contrary, am very idle, and feel inclined to do nothing but
stroll