(B) All the same, however, we must remember that where high elaboration of mechanism is concerned, the question as to the causes of its development become of more importance than those of its origin; e.g. even if self-adaptation be conceived capable of making a first step towards producing the exquisite mechanism of a bivalve shell, by discriminate variation, how is it conceivable that it should go on through the odd millions of successive steps of improvement needed to produce the perfect mechanism in which the great wonder of adaptation really occurs?
I can conceive of no natural process to accomplish this development even in one such case of mechanism other than natural selection. Let alone the 'endless variety' of elaborate mechanism elsewhere.
(C) Of course, if you could prove that indiscriminate variations have not occurred in wild plants, but only under cultivation, you would destroy Darwinism—in toto. But is the proposition credible a priori; or sustainable a posteriori, &c.?
I suppose you have read Wallace on the subject as regards wild animals, and if you were to make similar measurements with regard to wild plants, you would obtain analogous results.
I remember as a boy having a game of who could find most specimens of fern-leaved clover in a given time, or even two leaves of clover which would be exactly alike in all respects. But I have already discussed the matter of definite and indefinite variability in 'Darwin and after Darwin.'
(D) I will let the question of Use-Inheritance in relation to seemingly Passive Organs, go by default against me, as it is rather a side issue and would need much writing to discuss. The same applies to your remarks on Teleology. As regards both points I agree with your observations.
(E) Touching varieties as found in different areas from parent types, I suppose you heard how carefully Nägeli has gone into the subject, with the result that after making allowances for defects of isolation, change of environment, &c., only about five per cent. of species of plants seem to have originated on distant areas, while Wallace has shown that some such proportion applies to animals.
(F) As regards plants having been brought under cultivation, and yielding variations that prove heredity, I knew there were innumerable cases where artificial selection had been brought into play. But of course they are all out of court until the question on which you are engaged has been decided in your favour, i.e. until you have succeeded in disproving natural selection as analogous or parallel to artificial. It was for this reason I mentioned the case of parsnips, where the hereditary variations seem to have taken place in the first generation after transplanting, and therefore without leaving time for selection of any kind to have come into play.
Hôtel Costebelle, Hyères: March 29.