From Friedrich Hildebrand   11 May 1866

Bonn

May 11th 1866

Most honoured Sir

I must thank you for your very kind letter in which you approved my lastly published papers;1 I expect the copies of a little treatise on the Trimorphismus of Oxalis, to send you one of them: a great many of the former species were only founded on the different length of the styles and therefore must be united.2 It is a pity that the Oxalis are not much to be found in the gardens, I could not get of any more than one form (fresh specimens) and have only experimentized with the long-styled form of Oxalis rosea.3

I am sorry that I cannot follow the invitation to your botanical congress, from the Program I see that you will be there as Vice President4— perhaps you will have an opportunity to read the adjoining notices of the fertilisation of Corydalis cava, I hope the results of my experiments will be of some interest for you and some other botanist.—5 I am very glad to see by your letter, written with your own hand that you are quite recovered now, with my best wishes for your further health

I remain | dear Sir | yours | F Hildebrand

1
Hildebrand 1866a and 1866b. See letter to Friedrich Hildebrand, 20 April [1866].
2
Hildebrand refers to Hildebrand 1866c. CD’s heavily annotated copy is in the Darwin Pamphlet Collection–CUL. Hildebrand criticised existing classifications of Oxalis in which style length had been used as a species characteristic, and species descriptions had been based on only a few specimens (ibid., p. 353). See letter to Friedrich Hildebrand, 16 May [1866] and n. 10.
3
Although Hildebrand only experimented with the long-styled form, he stated that had he been able to cross other forms, it was ‘highly probable’ that the results would have been analogous to those that CD had obtained with Lythrum salicaria (Hildebrand 1866c, p. 373; see also ‘Three forms of Lythrum salicaria’). CD summarised Hildebrand’s experiments with O. rosea in Forms of flowers, pp. 178–9, noting, ‘The same rule holds good with Oxalis as with Lythrum salicaria; namely, that in any two unions, the greater the inequality in length between the pistils and stamens … the less fertile is the union.’
4
CD had been asked to join the committee of the International Horticultural Exhibition and Botanical Congress, held in London from 22 to 31 May 1866 (see letter from M. T. Masters, March 1866). CD did not attend the meeting; however, he is listed as a vice-president in the International Horticultural Exhibition 1866, p. 16.
5
Hildebrand’s paper ‘On the necessity for insect agency in the fertilisation of Corydalis cava’ was published in the International Horticultural Exhibition 1866, pp. 157–8 (Hildebrand 1866d). A copy of the paper is in the Darwin Pamphlet Collection–CUL. An expanded version of the paper was also published in German (Hildebrand 1866–7b); a copy is in the Darwin Pamphlet Collection–CUL. A brief notice of the paper appeared in the 2 June 1866 issue of Gardeners’ Chronicle, p. 516; CD underlined the passage in which Hildebrand reported that perfect fertilisation was only ensured by crossing flowers on different plants. CD’s annotated copies of the Gardeners’ Chronicle are in the Cory Library, Cambridge Botanic Garden.

Please cite as “DCP-LETT-5087,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-5087