He and L. C. Treviranus have repeated many of CD's orchid observations with the same results. Sends his paper ["Fruchtbildung der Orchideen", Bot. Ztg. 21 (1863): 329–33, 337–45].
induced by your work on the fertilisation of Orchids I have made some interesting observations, not so much respecting the fertilisation by insects as the effects of the pollen applied to the stigma. Therefore I venture to send you an extract of a little treatise that is going to be printed in <the> Botanische Zeitung, and I shoul<d be> very much obliged to you if <you> would read it in one of <your> botanical societies, or g<et it> printed anywhere.—
This last summer Professor Treviranus and myself have made observations on almost all the Orchids of our flora and can verify almost all you have said about them. We observed also the selffertilisation of Ophrys apifera, I suppose Professor Treviranus will tell you more about it, as he would not believe at first in this selffertilisation.
I am very much inclined to believe with you that there are certain Orchids as Acropera and Catasetum with their sexes separated, but after having read my observations you will agree with me that the absence or the incomplete state of the ovules <can>not be called a proof for the <ma>le sex of the plant. I am sure <you> will find the ovules very <incomp>letely developped in almost <any tropi>cal Orchid you will look at.
Your very interesting experiments on Linum perenne I have made with the same result. I had a plant of the short-styled form in my room, a part of the flowers were fertilised with each other, another part each flower with itself, and of both kinds of fertilisation I got no capsule; a third part of flowers on the same plant I fertilised with pollen of the long styled form and got a good capsule of almost every flower.— With my experiments on Primula I have not come to an end as yet.
I hope you will excuse my letter the more as I remember the kind answer I got on my former letter to you about the German translation of your Fertilisation of Orchids, and remain dear Sir | yours | respectfully | F Hildebrand
- f1 4242.f1Orchids.
- f2 4242.f2The enclosure has not been found. The German version of Hildebrand's paper was published in the Botanische Zeitung on 30 October and 6 November 1863 (Hildebrand 1863a). In it Hildebrand discussed his observations of two independent effects of pollen in orchids, namely, the enlargement of the ovary and the fertilisation of the ovules. CD sought Daniel Oliver's advice about the suitability of the English abstract of Hildebrand's paper for the Linnean Society or the Natural History Review (see letter to Daniel Oliver, 18 July , and letter from Daniel Oliver, 20 July 1863). It was ultimately published, through CD's intervention, in the September number of the Annals and Magazine of Natural History (Hildebrand 1863b; see letter to Friedrich Hildebrand, 28 July ).
- f3 4242.f3On Ludolph Christian Treviranus's reaction to Orchids, see also the letter from L. C. Treviranus, 12 February 1863, Treviranus 1863a, and Junker 1989, pp. 143--4.
- f4 4242.f4CD described the bee ophrys (Ophrys apifera) in Orchids, pp. 63--72, stating that he found the plant `perplexing in an unparalleled degree', since the flowers appeared to have `elaborate contrivances for directly opposed objects', namely for both cross- and self-pollination. See also letter to P. H. Gosse, 2 June  and n. 12. No letter from Treviranus on O. apifera has been found, but he questioned CD's findings in Treviranus 1863a, pp. 11--12, and later confirmed them in Treviranus 1863c. There are annotated copies of these papers in the Darwin Pamphlet Collection--CUL, and a manuscript translation of the latter in DAR 70.38. CD cited Treviranus's confirmation of his results in `Fertilization of orchids', p. 145 (Collected papers 2: 142).
- f5 4242.f5In Orchids, CD identified four species of orchids that were dioecious, the male plants being known by the specific names Acropera luteola, Catasetum saccatum, C. callosum, and C. tridentatum (Orchids, pp. 203--48). One of CD's reasons for believing these plants to be male was that the ovules were in an atrophied condition (see Orchids, pp. 207--8 and 238). In his paper, Hildebrand observed that the ovules of recently expanded orchid flowers exhibited very varying degrees of development (Hildebrand 1863b, p. 171). John Scott had already convinced CD that A. luteola was hermaphrodite (see letter to P. H. Gosse, 2 June ). In `Fertilization of orchids', p. 153 (Collected papers 2: 150), CD accounted for his error in terms of his ignorance of the `remarkable fact', established by Hildebrand, that `in many orchids the ovules are not developed until several weeks or even months after the pollen-tubes have penetrated the stigma'.
- f6 4242.f6In his paper, Hildebrand observed that in some tropical orchids he had examined, he found no ovules in the ovary of the expanded flower, but nevertheless saw `the enlargement of the ovarium after having applied the pollen to the stigma' (Hildebrand 1863b, p. 169).
- f7 4242.f7`Two forms in species of Linum'.
- f8 4242.f8Hildebrand published his observations on dimorphism in Linum perenne and Primula sinensis in January 1864 (Hildebrand 1864), offering them as a confirmation of CD's views. CD had written on P. sinensis in his paper `Dimorphic condition in Primula'.
- f9 4242.f9CD's letter to Hildebrand has not been found. Not realising that Heinrich Georg Bronn had already concluded his German translation of Orchids (Bronn trans. 1862) before his death on 5 July 1862, Hildebrand had offered to complete it (see Correspondence vol. 10, letter from Friedrich Hildebrand, 14 July 1862).