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Darwin Correspondence Project

To Fritz Müller   [late December 1866 and] 1 January 18671

Down. | Bromley. | Kent. S.E.

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 shd regretrvations & to see the dried flowers; nevertheless I shd 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 wd 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 yr 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 shd 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 Dr 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 yr 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.


The date is established by the postscript.
Müller sent a list of dimorphic plants he had recently found (see letter from Fritz Müller, [2 November 1866]).
CD was working on the final chapter of Variation (see CD’s ‘Journal’ (Correspondence vol. 14, Appendix II)). CD wrote a further paper (‘Illegitimate offspring of dimorphic and trimorphic plants’) and eventually a book on this subject (Forms of flowers). (Müller sent CD dried flowers of some of the plants he referred to in his letter (see letter from Fritz Müller, [2 November 1866] and n. 1). A species of Plumbago was one of those identified by Müller as dimorphic.
Müller had written in an earlier letter about a species of Oxalis that he thought was dimorphic (see letter from Fritz Müller, 1 and 3 October 1866 and nn. 2 and 6).
In his German translation of Müller’s letter, Alfred Möller refers to the plant as Ipomoea (see letter from Fritz Müller, [2 November 1866] and n. 11).
Müller’s remarks on Gesneria were contained in a now missing part of his letter of [2 November 1866]. He later sent CD seeds of Gesneria pendulina; CD reported the results of his experiments with this species in Cross and self fertilisation, pp. 92, 322.
Müller had described his observations on Eschscholzia californica, noting its infertility with pollen of the same individual plant (see letters from Fritz Müller, 2 August 1866 and [2 November 1866]).
Müller’s remarks on Oncidium were contained in a now missing part of his letter of [2 November 1866]. For his additional remarks on this orchid genus, see the letter from Fritz Müller, 1 December 1866.
Müller had speculated that in many orchids the ovules were in a rudimentary state when the flower first opened and only developed weeks later to a stage where they were ready for fertilisation (see letter from Fritz Müller, 2 August 1866).
CD had received bulbils of Oxalis sent by Müller in October 1866 (see letter to Fritz Müller, [before 10 December 1866] and n. 2).
CD had offered to send the first two parts of Genera plantarum by George Bentham and Joseph Dalton Hooker (Bentham and Hooker 1862–83; see letter to Fritz Müller, 23 August [1866]).
Müller had sent the seeds with his letter of 1 and 3 October 1866 (see letter to Fritz Müller, [before 10 December 1866], and letter to J. D. Hooker, 10 December [1866] and n. 3).
The reference is to Müller’s paper on climbing plants, which had been sent to the Linnean Society by CD (F. Müller 1865b; see also Correspondence vol. 13, letter from Fritz Müller, [12 and 31 August, and 10 October 1865]). CD planned to send copies of the paper to the Botanische Zeitung, the American Journal of Science and Arts, and the Bulletin de la Société Botanique de France (see letter to Fritz Müller, 23 August [1866] and n. 8).


Thanks for observations on dimorphic plants. Dimorphism prevalent in certain groups throughout the world.

Retarded fertilisation in certain orchids.

Letter details

Letter no.
Charles Robert Darwin
Johann Friedrich Theodor (Fritz) Müller
Sent from
Source of text
British Library (Loan 10: 11)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 5331,” accessed on 17 December 2017,

Also published in The Correspondence of Charles Darwin, vol. 14