Explains dichogamy in Aristolochia. C. K. Sprengel was wrong.
Dear and honoured Sir
I received your kind letter this morning, but I am very sorry that I cannot satisfy your wishes about the seeds of Oxalis rosea, I spent all of them this spring to see what forms I might get from the seeds produced by the three different manners of fertilisation—all of them were long-styled like the mother-plants. I have not made any other experiments about this matter and I am really sorry that I cannot send you the wanted seeds.— Perhaps it will interest you that I have experimentized last summer, besides other plants, with the flowers of Aristolochia Clematitis. Sprengel has made a mistake when thinking that each flower of this species is fertilised by insects agency with its own pollen. My observation have shown to me quite the contrary, for we have here a very interesting and curious case of ``weiblich-männlich Dichogamia. When the flower openes only the stigma is ripe, the anthers are not opened as yet and besides secured by the form of the kettle from the insect's touch. Some time after this first state of the flower the stigmatic surface besides withering is turned upwards and rolled up in a way that it cannot be touched any more, now the anthers open and can be touched by the insect because the under part of the kettle has become larger and is moved away from them. Now the hairs in the corollas mouth wither and the little flies get out, covered with pollen, to bring it now to the open stigma of a younger flower; the fertilisation with the flowers own pollen is quite impossible.
This case of dichogamie is quite different from the others known as yet, because the insect must wait in the flower the stigma of which it has fertilised, till the anthers of this same flower are opened— I hope that I shall be able to publish some thing about this matter, where the figures will make clearer this curious construction—but I fear it shall last again some time before I can sent you something about it; you have seen how long the publication of my paper on Oxalis has been delayed, that was written on the end of the last year.
I was very glad to see by the letter written with your own hand that you are recovered now, sending you my best wishes for your further health
I remain | dear Sir | yours | truly | F Hildebrand
- f1 5254.f1CD's letter requesting seeds of Oxalis rosea has not been found, but in an earlier letter he had asked for details of Hildebrand's recent paper on Oxalis (Hildebrand 1866c; see letter to Friedrich Hildebrand, 22 July ). Hildebrand had already informed CD that he had only been able to experiment with a single form of O. rosea (see letter from Friedrich Hildebrand, 11 May 1866 and n. 3). He later sent CD a copy of the paper, which included information on pollination experiments with the long-styled form of O. rosea, including the amounts of seed produced by artificially self-pollinating and cross-pollinating flowers with pollen from `upper and lower anthers'; that is, longer and shorter stamens (Hildebrand 1866c, pp. 371--4; see letter from Friedrich Hildebrand, 24 July 1866).
- f2 5254.f2Hildebrand had given CD a brief description of his observations on Aristolochia clematitis in his letter of 24 July 1866.
- f3 5254.f3Hildebrand refers to Sprengel 1793, pp. 418--29. CD first recorded reading Sprengel 1793 in 1841 (see Correspondence vol. 4, Appendix IV). His annotations on Christian Konrad Sprengel's comments on Aristolochia clematitis indicate that he was sceptical about several points in the account. For example, he questioned whether flies were really imprisoned in the flower and queried, `Why do so few flowers, then, produce seed which he has insisted on as explained?' (annotations to Sprengel 1793, pp. 423, 425; CD's copy is in the Darwin Library--CUL; for all CD's annotations on A. clematitis in Sprengel 1793, see Marginalia 1: 777, 784--5). See also letter from Friedrich Hildebrand, 24 July 1866.
- f4 5254.f4The literal translation is `female--male dichogamy'. Sprengel had used this expression to refer to the development of the pistil before the stamens (see Sprengel 1793, p. 19). Hildebrand later coined the word `protogyny'; see Hildebrand 1867, pp. 16--17 n. 3.
- f5 5254.f5Hildebrand reported his observations of dichogamy in Aristolochia clematitis in Hildebrand 1866--7a. CD's annotated copy of the article is in the Darwin Pamphlet Collection--CUL. CD referred to Hildebrand's demonstration of the cross-pollination of Aristolochia in Cross and self fertilisation, p. 417, but he did not cite the article. See also letter to Fritz Müller, [9 and] 15 April 1866 and n. 8.
- f6 5254.f6Hildebrand had explained the delay in publication of Hildebrand 1866c in his letter of 24 July 1866.
- f7 5254.f7CD's letter has not been found, but his earlier letter to Hildebrand of 22 July  was written by an amanuensis.