My dear M^r. Bentham

I have been extremely much pleased by your letter, and I take it as a very great compliment that you should have written to me at such length. I have been much interested by many of your details, though I regret greatly that I did not know your facts about the varieties of the ass, kidney-bean & artichoke before I published. Many thanks also for your references, but it is a great drawback to me that I have not strength to read nearly as much as I should wish.¹

I am glad to hear what you say about wheat, though I did not know that you believed it to be a descendant of Ægilops.²

I am not at all surprised that you cannot digest Pangenesis; it is enough to give any one an indigestion; but to my mind the idea has been an immense relief, as I could not endure to keep so many large classes of facts all floating loose in my mind without some thread of connection to tie them together in a tangible method.³

With respect to the men who have recently written on the crossing of Plants, I can at present remember only Hildebrand   Fritz Müller   Delpino & G. Henslow; but I think there are others.⁴ I feel sure that Hildebrand’s is a very good observer, for I have read all his papers & during the last 20 years I have made unpublished observations on many of the plants which he describes. Most of the criticisms which I sometimes meet with in French works against the frequency of crossing I am certain are the result of mere ignorance.⁵ I have never hitherto found the rule to fail that when an author describes the structure of a flower as a specially adapted for self-fertilization, it is really adapted for crossing. The Fumariaceæ offer a good instance of this, & Treviranus threw this order at my teeth, but in Corydalis Hildebrand shows how utterly false the idea of self fertilisation is.⁶ This author’s paper on Salvia is really worth reading & I have observed some species & know that he is accurate.⁷ Judging from a long review in the Bot. Zeitung & from what I know of some of the plants I believe Delpino’s article especially on the Apocyneæ is excellent: but I cannot read Italian.⁸

Perhaps you would like just to glance at such pamphlets as I can lay my hand on, & therefore I will send them as if you do not care to see them, you can return them at once; & this will cause you less trouble than writing to say you do not care to see them.

With respect to the Primulas the one point about which I feel positive is that the Bardfield & common oxslips are fundamentally distinct plants, & that the common oxslip is a sterile hybrid.⁹ I have never heard of the common oxslip being found in great abundance anywhere; & some amount of difference in number might depend on so small a circumstance as the presence of some moth which habitually sucked the primrose & cowslip.

To return to the subject of crossing; I am experimenting on a very large scale on the difference in power of growth between plants raised from self fertilised & crossed seeds; and it is no exaggeration to say that the difference in growth & vigour is sometimes truly wonderful.¹⁰ Lyell, Huxley & Hooker¹¹ have seen some of my plants & been astonished; & I should much like to show them to you. I always supposed until lately that no evil effects w^d be visible until after several generations of self fertilisation; but now I see that one generation sometimes suffices; & the existence of dimorphic plants & all the wonderful contrivances of orchids are quite intelligible to me.

With cordial thanks for your letter which has pleased me greatly | Your’s very sincerely | Charles Darwin

P.S. I heard some time ago from D^r. Hildebrand that he had succeeded in making a graft-hybrid, & I inserted this in the Reprint of my last book.— He will publish an account in Bot. Zeitung.¹² Tubers produced from buds of one kind inserted into a distinct kind, were hybridised or intermediate in characters. This seems to me a most important fact for any theory of generation, & supports Pangenesis.¹³ I am a firm believer & worshipper of my God Pan, & am convinced that all hereticks some day will be converted; but you hereticks are at present terribly numerous.—