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Darwin Correspondence Project

To Asa Gray   1 July [1862]1

Down Bromley Kent

July 1st.

My dear Gray

I have been baddish for 2 or 3 weeks, but am better tonight2 & mean to amuse myself (& have no other object) by scribbling a few lines on orchids. Since writing last, I have received your notes on Platanthera Hookeri & on diversity of forms of Cypripedium. On the latter you ought, if you can spare time, to write a paper.3 Platanthera Hookeri is really beautiful & quite a new case. It is almost laughable the viscid discs getting so far apart that the front of the flower has to be divided into two bridal chambers! I have added a note to the German Edition about this & a few words on Cypripedium on your authority.4 On getting your letter I wrote to Trübner to send the 12 dozen copies:5 I wish you would let me pay for them; but you are so punctilious that you would fling without permission first granted the money across the Atlantic in the same shameful manner in which you did the £8.—6

My son George, who is an entomologist, has been watching orchids with enthusiasm & indomitable patience.7 He has made out clearly that it is a Fly, (Empis) which fertilises O. maculata, & probably other Diptera fertilise the closely allied species; it was pretty to see the pollinia affixed to their spherical eyes, & after the act of depression parallel to & rather above the probosces.8 But the most remarkable case is that of Herminium monorchis; he has brought me 24 specimens of very minute Hymenoptera with pollinia attached to all, & always to the same exact spot—viz to the exterior base of femur of front legs. Nothing has given me such an idea of close adaptation of form of whole flower: the labellum hangs obliquely downwards & the minute insects enter between its Edge & the huge viscid disc on one side; & in retreating they hit their prominent femora against the under side of the disc. So closely fitted is the flower to the insect, that my son saw several times insects after entering in a wrong position come out, change their position & reenter.9 So much for orchids: I am fairly astonished at the success of my book (not that I know whether it sells) with Botanists: Berkeley has reviewed it in London R. rather egregiously, & Hooker writes strongly.10 So that now I can dismiss the subject & stick to other work.

Lately I have done very little, except some crossing of plants. I have made a great series of crosses on the peloric flowers of Pelargonium: but I doubt whether I shall get such good results, as I at first hoped with respect to sterility of hybrids.11 By the way Naudin writes that he is going to publish on this subject this autumn: his papers give me the idea that he does not know what has been done in Germany.—12 Rhexia glandulosa, I does require insect agency to set seed; but I see as yet no probability of dimorphism.13 You mentioned some genus (name forgotten without searching your letters) in which you found two forms like Primula, & a third form with both pistil & stamen short.14 Can you tell me whether all flowers on the specimen were thus characterised? I much want to know because Lythrum is trimorphic.—15

Yours ever most sincerely | C. Darwin


The year is established by the reference to the publication of the German translation of Orchids (see n. 4, below).
CD had been suffering from eczema (see letters to J. D. Hooker, 23 June [1862] and 30 [June 1862]).
The notes referred to have not been found; they may have been included with the letter from Asa Gray, [late June 1862]. Gray included information on Platanthera Hookeri in his review of Orchids (A. Gray 1862a, p. 143) and published observations on various species of Cypripedium in a follow-up article (A. Gray 1862b, pp. 427–8). See also letter to Asa Gray, 10–20 June [1862] and n. 16.
CD had sent Heinrich Georg Bronn, the German translator of Orchids, a list of corrections and additions to be included in the German edition (Bronn trans. 1862; see the second enclosure to the letter to H. G. Bronn, 30 June [1862]).
Gray had asked CD to arrange for six copies of Orchids to be sent to him by the publisher and bookseller, Nicholas Trübner, who frequently acted as Gray’s London agent (see letter to Nicholas Trübner, 23 June [1862]). Gray’s letter requesting the copies has not been found.
Gray had returned a payment resulting from the sale of his pamphlet on Origin (A. Gray 1861), the publication costs of which he and CD had shared (see letter from Asa Gray, 31 March [1862], and letter to Asa Gray, 21 April [1862]).
George Howard Darwin, then 16 years old, was on holiday from Clapham Grammar School. CD’s notes, dated 20–7 June 1862, recording George’s observations of the insects visiting several orchid species, are in DAR 70: 13–14, 30, 32–6 (see also nn. 8 and 9, below).
CD’s note recording George’s observations on flies visiting O. maculata, dated 20 June 1862, is in DAR 70: 13–14. CD reported these findings in the German edition of Orchids (Bronn trans. 1862, p. 22 n.; see the second enclosure to the letter to H. G. Bronn, 30 June [1862]). He later published them in ‘Fertilization of orchids’, p. 142 (Collected papers 2: 139–40).
The records kept by CD of George’s observations on insects visiting H. monorchis, dated 22–7 June 1862, are in DAR 70: 32–6 (see also letter from Frederick Smith, 28 June 1862); these observations were incorporated in the German edition of Orchids (Bronn trans. 1862, pp. 47–8 n.), and were later described in ‘Fertilization of orchids’, pp. 145–6 (Collected papers 2: 142–3). CD’s notes on his own observations of the species, dated 2 July 1862, are in DAR 70: 37.
See letter from J. D. Hooker, 28 June 1862. CD refers to Miles Joseph Berkeley’s review of Orchids, which appeared in the London Review and Weekly Journal of Politics, Arts and Science 4 (1862): 553–4.
CD had begun a series of crossing experiments with the normally sterile central peloric flowers of different varieties of pelargonium on 11 May 1862 (see the experimental notes in DAR 51 (ser. 2): 4–9, 12–13; see also letter to Daniel Oliver, 8 June [1862]); in 1861 he had attempted to encourage readers of the Gardeners’ Chronicle to carry out such experiments (see Correspondence vol. 9, letter to Journal of Horticulture, [before 18 June 1861]). The results of CD’s experiments are given in Variation 2: 167, as part of a discussion on the relationship between abnormal plant structure and the incidence of sterility. For CD’s interest in the causes of sterility, see Correspondence vol. 10, Appendix VI.
See letter from C. V. Naudin, 26 June 1862 and n. 4. CD probably refers to the experiments of the German hybridisers Karl Friedrich von Gärtner and Joseph Gottlieb Kölreuter.
Suspecting that plants of the melastomaceous genus Rhexia might exhibit a novel form of dimorphism, CD asked Gray to make observations for him; Gray promised to do so in the summer (see letters to Asa Gray, 16 February [1862] and 15 March [1862], and letter from Asa Gray, 6 March [1862]). Later, CD asked Gray if he would cover his plant under a net ‘& see if it seeded as well as uncovered plants’ (letter to Asa Gray, 21 April [1862]). However, having obtained a specimen of R. glandulosa (a synonym of Monochaetum floribundum), CD began a series of crossing experiments on 1 June 1862 (see the experimental notes, dated 1 June – 2 July 1862, in DAR 205.8: 14–15, and letter to Asa Gray, 10–20 June [1862]).
CD had discovered that Lythrum salicaria and L. thymifolia were trimorphic in December 1861, on reading Lecoq 1854–8 (see Correspondence vol. 9, letter to J. D. Hooker, 18 [December 1861]), and had obtained specimens for experiment from the Royal Botanic Gardens, Kew (see letter to J. D. Hooker, 22 [March 1862]). He had previously informed Gray of the case in his letter of 22 January [1862].


Collected papers: The collected papers of Charles Darwin. Edited by Paul H. Barrett. 2 vols. Chicago and London: University of Chicago Press. 1977.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

‘Fertilization of orchids’: Notes on the fertilization of orchids. By Charles Darwin. Annals and Magazine of Natural History 4th ser. 4 (1869): 141–59. [Collected papers 2: 138–56.]

Lecoq, Henri. 1854–8. Études sur la géographie botanique de l’Europe et en particulier sur la végétation du plateau central de la France. 9 vols. Paris: J. B. Baillière.

Orchids: On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing. By Charles Darwin. London: John Murray. 1862.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.


Thanks for notes on Cypripedium and Platanthera hookeri, which is really beautiful and quite a new case.

His son, George, has been observing the insect fertilisation of orchids.

CD has been crossing peloric flowers of Pelargonium, but doubts he will get good results with respect to sterility of hybrids.

Rhexia glandulosa does not appear to be dimorphic. Lythrum is trimorphic.

Letter details

Letter no.
Charles Robert Darwin
Asa Gray
Sent from
Source of text
Gray Herbarium of Harvard University (69)
Physical description
ALS 6pp

Please cite as

Darwin Correspondence Project, “Letter no. 3634,” accessed on 23 July 2024,

Also published in The Correspondence of Charles Darwin, vol. 10