Made aware by Asa Gray of error with respect to Cypripedium. Does not doubt it is self-fertilised.
Down, Bromley, Kent
— — — — I was made aware by Prof. Asa Gray (either in a paper in the Amer. Journal of Science or in a letter) of my error with respect to Cypripedium. By an odd chance I put an Andrena into the labellum, and saw what you describe as naturally taking place. — — — —
— — — I do not doubt that this species is generally self-fertilized; and I am aware that I erred in supposing that this happened to so few species. Neottia nidus avis is often self-fertilized. Epipactis latifolia I find is always fertilized by wasps. (vespa) — — — —
Yours very faithfully | Charles Darwin
- f1 5608.f1The year is established by the reference, in the letter to Fritz Müller, 15 August , to a letter from Hermann Müller containing observations on the fertilisation of orchids. Hermann began his work on orchids in the summer of 1867 (Möller ed. 1915--21, 2: 111).
- f2 5608.f2In Orchids, pp. 274--5, CD had speculated on the means by which flowers of Cypripedium might be pollinated, concluding that an insect would have to insert its proboscis through one of two small openings above the lateral anthers. Gray concluded, from observations of American species of Cypripedium, that an insect would enter a flower through the large opening on the dorsal surface of the flower, then crawl out through one of the small openings above the anthers (see Correspondence vol. 10, letter to Asa Gray, 10--20 June  and n. 16). Gray later published his observations in the American Journal of Science and Arts (A. Gray 1862).
- f3 5608.f3In Orchids 2d ed., pp. 230--1, CD described his experiment with a small bee of the genus Adrena and referred to the observations of Gray and Müller (see also Correspondence vol. 11, letter to Asa Gray, 20 April ). In the published version of his observations on Westphalian orchids, Müller described the pollination of Cypripedium calceolum, noting that the bee's path through the flower necessitated its touching the stigma before the anthers, thus ensuring cross-fertilisation (H. Müller 1868, pp. 1--3).
- f4 5608.f4The reference is probably to Müller's observations on Epipactis viridiflora (see H. Müller 1868, pp. 7--10, and Orchids 2d ed., pp. 102--3). Müller observed that the flower lacked a rostellum, which in most orchids separates the anther from the fertile stigma, and so was easily self-pollinated. In Orchids, p. 358, CD had concluded that self-fertilisation in orchids was a `rare event', but in the second edition he modified his view, acknowledging that some species were `regularly or often self-fertilised' (Orchids 2d ed., p. 290).
- f5 5608.f5In Orchids 2d ed., p. 290, CD included Neottia nidus-avis among those species capable of self-pollination, but more often pollinated by insects.
- f6 5608.f6In Orchids 2d ed., pp. 101--2, CD noted that wasps were the only insects he had seen visiting Epipactis latifolia. Müller cited CD's letter informing him of this fact in his paper on Westphalian orchids (H. Müller 1868, p. 12).