To Hermann Müller¹ 16 August [1867]²

Down, Bromley, Kent

Aug: 16.

Dear Sir

Ich bin Ihnen für Ihren höchst interessanten Brief sehr verbunden, aber es macht mir Sorge, dass Sie sich so viele Arbeit gemacht haben, mich zu verpflichten. … Sie theilen offenbar Ihres Bruders wundervolle Beobachtungsgabe, sowie seine Fertigkeit, sich englisch auszudrücken und seine Geschicklichkeit im Zeichnen. Ich hoffe, dass Sie Ihre excellente Beschreibung veröffentlichen werden.³ 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.⁴ By an odd chance I put an Andrena into the labellum, and saw what you describe as naturally taking place.⁵ Ich kann nicht umhin, ein wenig an der Vergiftung der Bienen zu zweifeln, da es die Ueberführung des Pollens von Pflanze zu Pflanze durchkreuzen würde Bienen sterben, wenn sie stark angestrengt werden, bald an Erschöpfung. Der grosse Robert Brown behauptet indessin, dass der Nektar der Asclepias Bienen vergifte, und das unterstützt Ihre Ansicht.⁶ Sie erwähnen nicht der wohlangepassten Einwärtskrümmung des Randes der Lippenöffnung, welche die Insekten verhindert, herauszukriechen.⁷

Ihre Beobachtungen an Epipactis erscheinen mir noch werthvoller. E. viridiflora scheint in demselben Falle wie Cephalanthera zu sein, aber man kann von dem Vorhandensein des Nektars daselbst schliessen, dass Insekten gelegentlich Pollen von Pflanze zu Pflanze führen. Könnten Sie nicht mit Anwendung des Pollens einer verschiedenen Pflanze und andererseits ihres eigenen experimentiren, und den Inhalt der Kapseln vergleichen? 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.⁸ Neottia nidus avis is often self-fertilized.⁹ Epipactis latifolia I find is always fertilized by wasps (vespa)¹⁰ — — — —

Yours very faithfully | Charles Darwin

Footnotes

The English parts of this letter, from a copy made for Francis Darwin, were previously published in Correspondence vol. 15; the German translation of some missing parts were later transcribed from Krause 1884. For a translation of the German of the printed source, see Appendix I.

The year is established by the reference, in the letter to Fritz Müller, 15 August [1867] (Correspondence vol. 15), 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).

Müller’s letter has not been found (see n. 1, above). Müller published his observations, with two plates illustrating the reproductive morphology of the orchids mentioned, in ‘Beobachtungen an westfälischen Orchideen’ (Observations on Westphalian orchids; H. Müller 1868).

In 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 [1862] and n. 16). Gray later published his observations in the American Journal of Science and Arts (A. Gray 1862).

In 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 [1863]). In the published version of his observations on Westphalian orchids, Müller described the fertilisation of Cypripedium calceolus (lady’s slipper), 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).

In H. Müller 1868, pp. 4–5, Müller described his observations and initial conclusion that the odour of the lady’s slipper orchid had killed the honey-bee. He added CD’s observation about the design of the rim of the labellum and concluded that the death of the honey-bees was due to the fact that they could not exit in the same manner as the smaller Adrena bees, through the narrow posterior openings, and simply died of exhaustion. Brown had written a paper, ‘On the organs and mode of fecundation in Orchideæ and Asclepiadeæ’ (Brown 1831), but he did not mention his observation on the nectar of Asclepias (milkweed).

In his published paper, Müller described the inward curvature of the rim of the labellum (see H. Müller 1868, p. 2).

Müller’s observations on Epipactis viridiflora (a synonym of E. purpurata, violet helleborine) were published in 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).

In Orchids 2d ed., p. 290, CD included Neottia nidus-avis (bird’s-nest orchid) among those species capable of self-fertilisation, but more often fertilised by insects.

Vespa is a genus in the family Vespidae (hornets, paper wasps, potter wasps, yellowjackets). In Orchids 2d ed., pp. 101–2, CD noted that wasps were the only insects he had seen visiting Epipactis latifolia (a synonym of E. helleborine, broad-leaved helleborine). Müller cited CD’s letter informing him of this fact in his paper on Westphalian orchids (H. Müller 1868, p. 12).

Bibliography

Brown, Robert. 1831b. On the organs and mode of fecundation in Orchideæ and Asclepiadeæ. [Read 1 and 15 November 1831.] Transactions of the Linnean Society of London 16 (1833): 685–745.

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

Gray, Asa. 1862a. [Review of Orchids.] American Journal of Science and Arts 2d ser. 34: 138–44, 420–9.

Krause, Ernst. 1884. Hermann Müller von Lippstadt: ein Gedenkblatt. Lippstadt: P. Rempel’s Buchhandlung (E. Hegener).

Möller, Alfred, ed. 1915–21. Fritz Müller. Werke, Briefe und Leben. 3 vols in 5. Jena: Gustav Fischer.

Müller, Hermann. 1868. Beobachtungen an westfälischen Orchideen. Verhandlungen des naturhistorischen Vereines der preussischen Rheinlande und Westphalens (Botanik) 25: 1–62.

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.

Translation

To Hermann Müller¹ 16 August [1867]²

Down, Bromley, Kent

Aug: 16.

Dear Sir

I am very grateful to you for your most interesting letter, but I worry that you have given yourself so much work in order to oblige me. … You obviously share your brother’s wonderful powers of observation, as well as his proficiency in expressing himself in English and his skill in drawing. I hope that you will publish your excellent description.³ 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.⁴ By an odd chance I put an Andrena into the labellum, and saw what you describe as naturally taking place.⁵ I cannot help but doubt a little the poisoning of bees, since bees would die from crossing from flower to flower to transfer pollen, if they were overtaxed to the point of exhaustion. The great Robert Brown maintains, however, that the nectar of Asclepias poisons bees, and this supports your view.⁶ You do not mention the well adapted inward curvature of the edge of the opening into the labellum, which prevents insects from entering.⁷

Your observations on Epipactis seem to me even more valuable. E. viridiflora seems to be a similar case to Cephalanthera, but it is apparent from the presence of nectar there, that insects occasionally carry pollen from plant to plant. Could you not try an experiment with the application of pollen of a different plant and of its own, and compare the contents of the capsules? I do not doubt that this species is generally self-fertilised; and I am aware that I erred in supposing that this happened to so few species.⁸ Neottia nidus avis is often self-fertilised.⁹ Epipactis latifolia I find is always fertilised by wasps (vespa)¹⁰ — — — —

Yours very faithfully | Charles Darwin

Footnotes

The English parts of this letter, from a copy made for Francis Darwin, were previously published in Correspondence vol. 15; the German translation of some missing parts were later transcribed from Krause 1884. For a transcription of the German of the printed source, see Transcript.