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Letter 4003

Darwin, C. R. to Scott, John

20 [Feb 1863]

    Summary Add

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    Thanks JS for the very large Acropera capsule. CD has perhaps made a blunder about the sex of Acropera.

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    JS was right that successive homomorphic generations of Primula breed true.

Transcription

Down Bromley Kent

20th

Dear Sir

What a magnificent capsule & good Heavens what a number of seed! I never before opened pod of larger orchids. It did not signify a few seed being lost, as it would be hopeless to estimate number in comparison with other species.— If you sow any, had you not better sow a good many? so I enclose small packet.—

I have looked at seeds: I never saw in British orchid nearly so many empty testæ; but this goes for nothing as unnatural conditions wd. account for it. I suspect, however from variable size & transparency that a good many of the seeds when dry (& I have put capsule on my chimney piece) will shrivel up. So I will wait for a month or two till I get capsule of some large Vandeæ for comparison.—

It is more likely that I have made some dreadful blunder about Acropera than that it shd be male not yet a perfect male. May there be some sexual relation between A. Loddigesii & luteola; they seem very close? I shd. very much like to examine capsule of unimpregnated flower of A. Loddigesii.— I have got both species from Kew; but whether we shall have skill to flower them I know not— One conjecture that that it is imperfect male, I still shd. incline to think it would produce by seed both sexes.— But you are right about Primula (& a very acute thought it was) the long-styled P. Sinensis homorphically fertilised with own-form pollen, has produced during two successive homomorphic generations only long styled plants.— The short-styled the same ie produced short-styled for 2 generations with exception of a single plant.—

I cannot say about cowslip yet.—

I shd. like to hear your case of the Primula: is it certainly propagated by seed?

My dear Sir | Yours very faithfully | C. Darwin

    Footnotes Add

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    f1 4003.f1
    The date is established by the relationship between this letter and the letters from John Scott, 18 February [1863] and 3 March 1863.
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    f2 4003.f2
    Scott sent CD a seed capsule of the orchid Acropera loddigesii with his letter of 18 February [1863]. Scott had succeeded, where CD had failed, in effecting pollination in this genus (see Correspondence vol. 10, letter from John Scott, 11 November 1862, and this volume, letter to John Scott, 16 February [1863], n. 3).
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    f3 4003.f3
    In his letter of 18 February [1863], Scott explained that the seed-capsule of Acropera loddigesii (see n. 2, above), had matured earlier than he expected and burst open, and that he had lost a number of seeds in the process.
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    f4 4003.f4
    As Scott was packing the seed-capsule of the premature Acropera specimen (see nn. 2 and 3, above), `30 or so' of the seeds spilled into his hand; Scott planned to sow the seeds to see if he could raise the plants (see letter from John Scott, 18 February [1863]).
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    f5 4003.f5
    CD had been promised capsules of several Vanda species on his visit to the Royal Botanic Gardens, Kew, on 11 February 1863 (see letter to John Scott, 16 February [1863] and n. 14).
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    f6 4003.f6
    CD had repeatedly failed in his attempts to effect pollination in two species of Acropera, namely, A. loddigesii and A. luteola. From this fact, and from dissections of A. loddigesii and A. luteola, CD concluded that although no instance of the separation of the two sexes was known in orchids, these supposed species might actually be the male form of a dioecious species, of which the female form had not yet been identified (Orchids, pp. 206--9). After Scott had sent capsules of A. loddigesii containing viable seed, obtained by fertilising some flowers with pollen from the same plant, CD concluded that his former opinion was wrong, and that Acropera was a hermaphrodite (see letter from John Scott, 18 February [1863] and nn. 4 and 5, and `Fertilization of orchids').
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    f7 4003.f7
    In his letter of 18 February [1862], Scott posed the question: `If Acropera be the male incipient form, and not yet perfectly sterile, will it when self-impregnated produce both forms?' Reasoning from the example of the transmission of forms in homomorphically fertilised primroses (see n. 8, below), Scott was inclined to believe that the self-pollinated Acropera would not produce both sexes from seed.
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    f8 4003.f8
    Scott had observed that a self-pollinated variety of primrose in the Royal Botanic Garden, Edinburgh, produced only the long-styled form (see letter from John Scott, 18 February [1863]). Scott was aware that CD had made homomorphic crosses with generations of Primula sinensis (see Correspondence vol. 10, letter to John Scott, 3 December [1862] and n. 6). CD's observations on the transmission of the long-styled form in P. sinensis, based on trials conducted in 1862, were published in `Illegitimate offspring of dimorphic and trimorphic plants', pp. 410--11: I raised during February 1862, from some long-styled plants illegitimately fertilized by pollen from the same form, twenty-seven seedlings. These were all long-styled. They proved fully fertile or even fertile in excess&lldots; From the foregoing twenty-seven plants, fertilized by their own-form pollen, I raised twenty-five seedling grandchildren; and these were all long-styled; so that from the two illegitimate generations fifty-two plants were raised, and all without exception proved long-styled.
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    f9 4003.f9
    CD's experimental crosses with the short-styled Primula sinensis are detailed in `Illegitimate offspring of dimorphic and trimorphic plants', pp. 412--13. See also the experimental notes in DAR 108: 18, 27--8, 34--5.
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    f10 4003.f10
    CD had begun making homomorphic crosses with cowslips (Primula veris) in the spring of 1862 (see Correspondence vol. 10). CD's notes on these experiments are preserved in DAR 157a: 77 and DAR 108: 70. From his experiments CD concluded that `the short-styled form of the cowslip, when self-fertilized, does not transmit the same form nearly so truly as does that of P. sinensis'. The long-styled form, when self-fertilised, was transmitted in 148 of the 152 plants raised, consisting of four generations (`Illegitimate offspring of dimorphic and trimorphic plants', p. 423). See also the letter to John Scott, 24 March [1863].
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    f11 4003.f11
    See letters from John Scott, 18 February [1863] and 3 March 1863.
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