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Darwin Correspondence Project

To Roland Trimen   27 August [1863]1

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

Aug 27th

My dear Sir

I am very much obliged for your very pleasant letter.2 You have hit upon the right case in Oxalis, & seeds will really be a treasure to me.3 I have posted a paper for you on the dimorphism of Linum which if you will read, you will see why I am anxious for Oxalis4   I have a more curious case unpublished;5 but the whole class of facts strike me as very surprising. You may rely on my statements for they have been verifyed. Linum perenne agrees with your Oxalis.6 I am also very glad indeed to hear about the Peaches,7—the more so as it is an exotic in S. Africa.— I am going in a weeks time to Malvern for a month to try & get a little strength, & when there I will probably draw up a notice for Gardeners’ Chronicle on your peach case.—8

I daily expect proofs of your paper on Disa;9 a rough woodcut is made.— 10 You must not waste time in sending me many specimens of Orchids in spirits, for I declare I do not know whether I shall ever have time to work up mass of new matter already collected on Orchids. It is capital sport to observe & a horrid bore to publish.—

It pleases me to read your admiration on my beloved orchids—11 I quite agree they are intellectual beings! By the bye, I believe I have blundered on Cypripedium:12 Asa Gray suggested that small insects enter by the toe & crawl out by the lateral windows.—13 I put in a small bee & it did so & came out with its back smeared with pollen; I caught him & put him in again, & again he crawled out by the window: I cut open the flower & found the stigma smeared with pollen!—

Read Bates Travels14   they will,, I am sure, interest you.— With respect to Physianthus, I do not know whether fact is known; but I think it would be well worth investigating.15 It is certain that the Asclepiadæ require insect aid for fertilisation. The pollen-masses are wonderfully like those of Orchids. You ought to read R. Browns admirable paper on Asclepias in Transact. Linnean Soc. about 15 or 20 years ago.16 In the Apocyneæ, (which are allied to the Asclepiadæ) there is a genus, which catches Diptera by the hundred; I have a plant but cannot make it flourish, as I have always wished to investigate the case.17 It is said that the Diptera are caught by the wedge-shaped spaces between filaments of anthers. But I suspect that plant somehow profits or requires visits of insects. You ought to try whether Physianthus will seed if insects are excluded by a net.— I have seen Hymenoptera from N. America with numbers of pollen-masses of some Asclepias sticking to their tarsi; & the pollen-masses are thus dragged over the stigmas.— R. Brown’s paper has beautiful illustrations.—

This is a disjointed, dull letter, but I have been working all day with very little strength.—

With every good wish & sincere thanks | Pray believe me | My dear Sir | Yours sincerely | Ch. Darwin


The year is confirmed by the relationship between this letter and the letter from Roland Trimen, 16, 17, and 19 July 1863.
See letter from Roland Trimen, 16, 17, and 19 July 1863; Trimen had said that he would collect seeds of dimorphic species of Oxalis for CD. CD had been investigating dimorphism in species of Oxalis since 1861 (see Correspondence vols. 9 and 10).
‘Two forms in species of Linum; for CD’s presentation list for this paper, see Correspondence vol.11, Appendix IV.
CD refers to the existence of trimorphic flowers in species of Lythrum (see letter to J. D. Hooker, 3 August [1863] and n. 6). See also letter to Alphonse de Candolle, 4 August [1863], and letter to Asa Gray, 4 August [1863]. CD described his experiments on Lythrum in ‘Three forms of Lythrum salicaria, which was read before the Linnean Society on 16 June 1864 and published in Journal of the Proceedings of the Linnean Society (Botany) in December 1864 (General index to the Journal of the Linnean Society).
Trimen had sent CD sketches of the pistils of the two flower forms and the flowers of what he took to be Oxalis cernua (a synonym of O. pes-caprae, African wood-sorrel) with his letter to CD of 16, 17, and 19 July 1863. CD had discussed Linum perenne in ‘Two forms in species of Linum, pp. 75–81 (Collected papers 2: 98–103).
Trimen had written that moths often injured peaches in South Africa by penetrating the skins with their probosces; this was consistent with CD’s hypothesis that moth pollinators penetrated the inner walls of the spurs of certain species of orchids (see letter from Roland Trimen, 16, 17, and 19 July 1863 and n. 13, and Orchids, pp. 48–53). See also n. 8, below.
CD wrote a draft letter detailing Trimen’s observations, but the letter was not published (see following letter). CD cited Trimen’s observations in ‘Fertilization of orchids’, p. 143 (Collected papers 2: 140), and Orchids 2d ed., p. 40.
Trimen 1863, p. 145, carried a woodcut comprising four diagrams illustrating the structure of Disa grandiflora. The woodcut was made from Trimen’s sketches (see letter from Roland Trimen, 16 March 1863 and nn. 20 and 21, and letter to Roland Trimen, 23 May [1863]). These watercolour sketches are reproduced facing p. 246.
In his letter of 16, 17, and 19 July 1863, Trimen remarked that he had verified CD’s explanation of pollination in this orchid genus. CD described pollination in Cypripedium in Orchids, pp. 270–6, where he hypothesised that the pollinating insect would insert its proboscis at the base of the labellum directly over an anther.
See Correspondence vol. 10, letter to Asa Gray, 10–20 June [1862] and n. 16. Asa Gray’s observations on pollination mechanisms in Cypripedium were published in A. Gray 1862b. See also this volume, letter to Asa Gray, 20 April [1863] and n. 24, and letter from Asa Gray, 26 May 1863 and nn. 17, 18, and 20. CD modified his account of pollination in this genus in ‘Fertilization of orchids’, pp. 155–6 (Collected papers 2: 152–3), and Orchids 2d ed., pp. 229–31.
See letter from Roland Trimen, 16, 17, and 19 July 1863 and n. 21; Trimen had reported that the milkweed Physianthus albens, a member of the Asclepiadaceae, trapped insects that landed on its flowers.
The references are to Robert Brown and to Robert Brown 1833b.
The reference is to Apocynum androsaemifolium, which CD’s father, Robert Waring Darwin, had grown. See Correspondence vol. 8, letters to Daniel Oliver, 16 November [1860] and [21 November 1860], and letter from Daniel Oliver, 23 November 1860. CD did not discuss this species in Insectivorous plants.


Bates, Henry Walter. 1863. The naturalist on the River Amazons. A record of adventures, habits of animals, sketches of Brazilian and Indian life, and aspects of nature under the equator, during eleven years of travel. 2 vols. London: John Murray.

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.]

General index to the Journal of the Linnean Society: General index to the first twenty volumes of the Journal (Botany), and the botanical portion of the Proceedings, November 1838 to June 1886, of the Linnean Society. London: Linnean Society of London. 1888.

Insectivorous plants. By Charles Darwin. London: John Murray. 1875.

Orchids 2d ed.: The various contrivances by which orchids are fertilised by insects. By Charles Darwin. 2d edition, revised. London: John Murray. 1877.

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.

‘Three forms of Lythrum salicaria’: On the sexual relations of the three forms of Lythrum salicaria. By Charles Darwin. [Read 16 June 1864.] Journal of the Linnean Society (Botany) 8 (1865): 169–96. [Collected papers 2: 106–31.]

Trimen, Roland. 1863. On the fertilization of Disa grandiflora, Linn.... drawn up from notes and drawings sent to C. Darwin, Esq., FLS, &c. [Read 4 June 1863.] Journal of the Proceedings of the Linnean Society (Botany) 7 (1864): 144–7.

‘Two forms in species of Linum’: On the existence of two forms, and on their reciprocal sexual relation, in several species of the genus Linum. By Charles Darwin. [Read 5 February 1863.] Journal of the Proceedings of the Linnean Society (Botany) 7 (1864): 69–83. [Collected papers 2: 93–105.]


Discusses methods of pollination in orchids.

Thinks RT should investigate Physianthus to see if it requires insect aid for fertilisation as the Asclepiadaceae do.

Letter details

Letter no.
Charles Robert Darwin
Roland Trimen
Sent from
Source of text
Royal Entomological Society (Trimen papers, box 21: 57)
Physical description
ALS 7pp

Please cite as

Darwin Correspondence Project, “Letter no. 4279,” accessed on 23 February 2024,

Also published in The Correspondence of Charles Darwin, vol. 11