My dear Sir

Your letter of Nov 2. contains an extraordinary amount of interesting matter.² What a number of dimorphic plants S. Brazil produces; you observed in one day as many or more dimorphic genera than all the botanists in Europe have ever observed.³ When my present book is finished I shall write a final paper upon these plants, so that I am extremely glad to hear of your observations & to see the dried flowers; nevertheless I sh^d regret much if I prevented you from publishing on the subject. Plumbago is quite new to me, though I had suspected it.⁴

It is curious how dimorphism prevails by groups throughout the world, shewing as I suppose that it is an ancient character: thus Hedyotis is dimorphic in India: the two other genera in the same sub-family with Villarsia are dimorphic in Europe & Ceylon: a sub-genus of Erythroxylum is dimorphic in Ceylon ?& Oxalis with you & at the C. of Good Hope⁵  If you can find a dimorphic Oxalis it will be a new point, for all known species are trimorphic or monomorphic.⁶ The case of Convolvulus will be new if proved.⁷ I am doubtful about Gesneria & have been often myself deceived by varying length of pistil.⁸ A difference in the size of the pollen-grains w^d be conclusive evidence; but in some cases experiments by fertilization can alone decide the point. As yet I know of no case of dimorphism in flowers which are very irregular; such flowers being apparently always sufficiently visited & crossed by insects. Your case of the Eschholtzia is extremely curious.⁹ With Orchids I know of many facts like that which you give about Oncidium.¹⁰

Will you be so kind as to remember to tell me, when you next write, whether the Oncidium is an endemic species.

I do not know what to think about y^r curious speculation on the retarded fertilization of certain Orchids: I believe the pollen-tubes do not reach the ovule in some coniferous trees until many months have elapsed.¹¹ The little bulbs of the semi-sterile Oxalis have begun to grow & I hope will flower;¹² I sh^d suspect that their sterility was nearly of the same nature with that of many cultivated plants.

I have sent off Bentham’s & Hooker’s Genera by post to you.¹³ With respect to the scarlet seeds sent in a former letter I gave 2 to a fowl but they were ground up by its gizzard & disappeared. The remainder I sent to D^r Hooker; he knows the seeds well, & says they belong to an Indian plant the Adenanthera pavonina.¹⁴ Is it a garden-plant with you? The dissemination of its seeds is a puzzling problem.

With cordial thanks for all y^r great kindness believe me yours very sincerely | Charles Darwin

P.S. Jan 1 1867

By some unaccountable delay I have only this moment received copies of your paper. I will send off 3 copies as before stated;¹⁵ I transmit to you by this post 11 copies; I retain 10 copies any or all of which I will send as you may direct.