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Letter 5216

Darwin, C. R. to Müller, J. F. T.

25 Sept [1866]

    Summary Add

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    Fertilisation in orchids: Friedrich Hildebrand's paper.

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    Self-sterility.

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    Climbing plants.

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    Agassiz's attempts to eliminate all Darwinian views.

Transcription

Down Bromley Kent

Sep & 25th

My dear Sir

I have just recd your letter of Aug. 2nd & am as usual astonished at the number of interesting points which you observe. It is quite curious how by coincidence you have been observing the same subjects that have lately interested me.

Your case of the Notylia is quite new to me; but it seems analogous with that of Acropera, about the sexes of which I blundered greatly in my book. I have got an Acropera now in flower & have no doubt that some insect with a tuft of hairs on its tail removes by the tuft the pollinia, & inserts the little viscid cap & the long pedicel into the narrow stigmatic cavity, & leaves it there with the pollen-masses in close contact with, but not inserted into, the stigmatic cavity. I find I can thus fertilize the flowers; & so I can with Stanhopea, & I suspect that this is the case with your Notylia. But I have lately had an orchid in flower, viz. Acineta, which I could not any how fertilize. Dr Hildebrand lately wrote a paper shewing that with some orchids the ovules are not mature & are not fertilized until months after the pollen-tubes have penetrated the column; & you have independently observed the same fact, which I never suspected in the case of Acropera. The column of such orchids must act almost like the Spermatheca of insects. Your Orchis with 2 leaf-like stigmas is new to me; but I feel guilty at your wasting your valuable time in making such beautiful drawings for my amusement.

Your observations on those plants being sterile which grow separately or flower earlier than others are very interesting to me. They wd be worth experimenting on with other individuals: I shall give in my next book several cases of individual plants being sterile with their own pollen. I have actually got on my list Escholtzia for fertilizing with its own pollen, though I did not suspect it wd prove sterile, & I will try next summer. My object is to compare the rate of growth of plants raised from seed fertilized by pollen from the same flower & by pollen from a distinct plant & I think from what I have seen I shall arrive at interesting results. Dr Hildebrand has lately described a curious case of Corydalis cava, which is quite sterile with its own pollen, but fertile with pollen of any other individual plant of the species. What I meant in my paper on Linum about plants being dimorphic in function alone was that they shd be divided into two equal bodies functionally but not structurally different. I have been much interested by what you say on seeds which adhere to the valves being rendered conspicuous: you will see in the new Edit. of the origin why I have alluded to the beauty & bright colours of fruit; after writing this, it troubled me that I remembered to have seen brilliantly coloured seed, & your view occurred to me. There is a species of Peony in which the inside of the pod is crimson & the seeds dark purple. I had asked a friend to send me some of these seeds, to see if they were covered with any thing which cd prove attractive to birds. I recd some seeds the day after receiving your letter; & I must own that the fleshy covering is so thin that I can hardly believe it wd lead birds to devour them; & so it was in an analogous case with Passiflora gracilis. How is this in the cases mentioned by you? The whole case seems to me rather a striking one.

I wish I had heard of Mikania being a leaf-climber before your paper was printed; for we thus get a good gradation from M. scandens to Mutisia with its little modified leaf-like tendrils. I am glad to hear that you can confirm (but render still more wonderful) Haeckel's most interesting case of Liriope: Huxley told me that he thought that the case wd somehow be explained away.

As for Agassiz & his glaciers in the valley of the Amazons, it seems to me sheer madness, as it does likewise to Lyell; the evidence being wholly insufficient. Prof. Asa Gray tells me that A. started with the determination to prove that the whole world had been covered with ice in order to annihilate all Darwinian views.

I hope I have not troubled you with this long letter & believe me yours very sincerely

Charles Darwin

    Footnotes Add

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    f1 5216.f1
    The year is established by the relationship between this letter and the letter from Fritz Müller, 2 August 1866.
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    f2 5216.f2
    In his letter of 2 August 1866, Müller had discussed dimorphism in Brazilian species of Oxalis, self-sterility in various plants, and brightly coloured seeds.
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    f3 5216.f3
    In Orchids, pp. 203--10, CD described Acropera (now placed in synonymy with Gongora) as dioecious, concluding that the specimens he examined were male; however, in 1862 John Scott succeeded in pollinating flowers with pollen from the same plant. CD himself eventually pollinated Acropera (see Correspondence vol. 11, letter to John Scott, 7 November [1863] and n. 6, and the experimental note in DAR 70: 114). In August 1866, CD began experimenting with Acropera once more, and had recently been successful in pollinating a specimen (see letter to J. D. Hooker, 30 August [1866] and n. 11). Müller had reported that he initially supposed that a specimen of Notylia was male because he could not get pollinia to adhere to the stigma and the ovules seemed rudimentary, but that he later found seed capsules (see letter from Fritz Müller, 2 August 1866).
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    f4 5216.f4
    Müller later confirmed CD's description in experiments with Cirrhaea, a genus related to Acropera. He described the process by which the pollinium was gradually sucked into the stylar canal after one end was inserted into the narrow entrance of the stigmatic chamber (F. Müller 1868b, pp. 630--1). CD referred to Müller's description in `Fertilization of orchids', p. 153 (Collected papers 2: 150), and in Orchids 2d ed., p. 206. CD's annotated copy of F. Müller 1868b is in the Darwin Pamphlet Collection--CUL. For CD's finding on Stanhopea, see his notes, dated 11 to 20 August 1866, in DAR 70: 122--8, and Orchids 2d ed., p. 171; see also Correspondence vol. 12.
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    f5 5216.f5
    In a note written on 3 July 1866 (DAR 70: 117), CD described his inability to pollinate Acineta, another orchid genus related to Acropera, noting that the stigmatic opening was so small that pollen could hardly enter and would not stick. He concluded that he could not conceive how the flower was fertilised. In `Fertilization of orchids', p. 153, CD mentioned Acineta as one of the genera of orchids with a narrow entrance to the stigmatic chamber for which the means of pollination was not yet known, but added that insect agency of some kind was certain. For more on the pollination mechanisms of Acineta and the other orchid genera discussed in nn. 3 and 4, above, see Dressler 1981, pp. 102--3, 258--9.
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    f6 5216.f6
    Friedrich Hildebrand reported his results from pollinating and cross-pollinating several species of orchids in Hildebrand 1863 and 1865c. CD's annotated copies of both papers are in the Darwin Pamphlet Collection--CUL. Hildebrand concluded that pollen caused the ovary to swell and the ovule to develop, after which fertilisation could occur (Hildebrand 1865c, p. 249). CD cited Hildebrand's articles in `Fertilization of orchids', p. 153, and in Orchids 2d ed., p. 172. After observing specimens of Notylia as well as other orchids, Müller had suggested that the ovules of some orchids, especially among the tribe Epidendreae, did not develop until the flower had been opened for some time (see letter from Fritz Müller, 2 August 1866).
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    f7 5216.f7
    See letter from Fritz Müller, 2 August 1866 and n. 8.
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    f8 5216.f8
    The list of plants to which CD refers has not been found. Müller had observed some plants, including Eschscholtzia californica, all of which appeared to be sterile with their own pollen but fertile with pollen from another individual plant of the species (see letter from Fritz Müller, 2 August 1866). CD discussed self-sterility in Variation 2: 131--40, including many of Müller's findings.
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    f9 5216.f9
    See letter to Asa Gray, 10 September [1866] and n. 13.
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    f10 5216.f10
    Hildebrand had sent CD a copy of his paper on Corydalis cava (Hildebrand 1866d; see letter from Friedrich Hildebrand, 11 May 1866 and n. 5).
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    f11 5216.f11
    CD made the comment on functional dimorphism in `Two forms in species of Linum', p. 82 (Collected papers 2: 104). See also letter from Fritz Müller, 2 August 1866.
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    f12 5216.f12
    In Origin 4th ed., p. 240, CD argued that the beauty or bright coloration of fruit served `merely as a guide' to attract birds or mammals so that their seed might be disseminated. See letter to C. W. Nägeli, 12 June [1866] and n. 4. For more on CD's views on beauty see also the letter to James Shaw, 11 February [1866].
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    f13 5216.f13
    CD probably refers to his niece Lucy Caroline Wedgwood (see letter to L. C. Wedgwood, [before 25 September 1866] and n. 3).
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    f14 5216.f14
    Müller had discussed the brightly coloured seeds of various plants in his letter of 2 August 1866.
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    f15 5216.f15
    CD refers to F. Müller 1865b, which appeared in the 29 November 1866 issue of the Journal of the Linnean Society (Botany) (see letter from Frederick Currey, 5 July 1866 and n. 1). In Climbing plants 2d ed., pp. 116--17, CD added the information from Müller that a Brazilian species of Mikania was a leaf-climber; he noted the gradation in Climbing plants 2d ed., pp. 195--6.
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    f16 5216.f16
    Müller's remarks on Liriope were in a now missing section of his letter of 2 August 1866; however, in a letter to Ernst Haeckel of 3 June 1866 (Möller ed. 1915--21, 2: 84--6), Müller informed Haeckel that he had recently confirmed Haeckel's findings concerning reproduction in certain Hydromedusae species (Haeckel 1865d; see Correspondence vol. 13, letter to Ernst Haeckel, 6 December [1865] and n. 9). Haeckel claimed to have discovered a new form of alternation of generations, having observed the apparent budding of individuals of Cunina rhododactyla (now Pegantha rubiginosa) from a parent Geryonia hastata (now G. proboscidalis). Müller reported that he observed a parent of Liriope catharinensis (now with L. tetraphylla), a species closely related to G. hastata, with buds of C. köllikeri (now C. octonaria). Müller further observed that all the offspring were males of C. köllikeri and speculated whether, as in the case of some dimorphic plants, males of one form fertilised females of the other (see Möller ed. 1915--21, 2: 85). It is now generally accepted that larvae of C. octonaria develop parasitically in the stomach pouches of other medusae such as Liriope (see Kramp 1961, p. 282). Thomas Henry Huxley had worked on the anatomy and classification of the Medusae (see, for example, T. H. Huxley 1849).
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    f17 5216.f17
    Müller's comments about Louis Agassiz's theory that the Amazon valley had been covered by a glacier were in a now missing section of his letter of 2 August 1866; CD refers to his own recent correspondence with Charles Lyell discussing Agassiz's claims (see letter to Charles Lyell, 8[--9] September [1866] and n. 6).
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    f18 5216.f18
    See letter from Asa Gray, 27 August 1866; see also Lurie 1960, p. 345.
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