To George Henslow   16 April [1866]1

Down Bromley Kent

April 16

My dear Mr. Henslow

I received yesterday the Botanische Zeitung Nor 10 for March 9 1866 with paper by Dr. Hildebrand of Bonn, who describes carefully what you showed me in Indigofera!2 & it seems that the irritability had been described by De Candolle & Treviranus,—who, however, mistook the proportion—3 Hildebrand also describes analogous movement in Medicago & to certain extent in Cytisus.—4

I am sorry for this. Dr H. also sends me long paper with good engravings on Salvia5—but not yet read— All these are in German— In Haste

Yours very sincerely | Ch. Darwin

1
The year is established by the reference to the receipt of Botanische Zeitung for 9 March 1866.
2
Friedrich Hildebrand’s paper described mechanisms for insect pollination in Indigofera, Medicago, and other genera (Hildebrand 1866a). A lightly annotated copy is in the Darwin Pamphlet Collection–CUL. Henslow was preparing a paper in which he argued that the flowers of Indigofera were adapted to assist the pollination of one flower by another (Henslow 1866a). The published paper contained a discussion of Hildebrand 1866a, and a brief note by CD on similar mechanisms in Cytisus scoparius. Henslow commented that, although Hildebrand had described the same structure as ‘adapted for fertilization by insects’, he did not infer that it was ‘especially purposed for the intercrossing of distinct flowers’ (Henslow 1866a, p. 356). Henslow discussed Indigofera with CD during his visit to Down from 2 to 3 or 4 April 1866 (letter to Friedrich Hildebrand, 20 April [1866] and n. 3).
3
Hildebrand noted that Augustin Pyramus de Candolle and Ludolph Christian Treviranus had previously described the mechanism by which the stigma and stamens were released from the keel of the flowers of Indigofera, but had not noted that the mechanism permitted cross-pollination by insects (Hildebrand 1866a, pp. 74–5). Henslow also criticised Candolle and Treviranus in Henslow 1866a, pp. 356–7. CD may refer to the proportion of flowers pollinated without insect aid to those pollinated by insects.
4
See Hildebrand 1866a, pp. 74–5. Henslow had written a paper on pollination mechanisms in Medicago sativa (Henslow 1865). See Correspondence vol. 13, letters from George Henslow, 1 November 1865 and 6 November 1865.
5
The reference is to Hildebrand 1866b. CD’s heavily annotated copy is in the Darwin Pamphlet Collection–CUL. Henslow had described the movement of the anthers and stigma that facilitated insect pollination in Salvia in his letter to CD of 1 November 1865 (Correspondence vol. 13). On CD’s interest in Salvia, see ibid., letter from George Henslow, 6 November 1865, n. 3.

Please cite as “DCP-LETT-5058,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5058