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Letter 4929F

Darwin, C. R. to Henslow, George

[2–5 Nov 1865]

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    Reports the results of an experiment to compare the weight of seeds produced in plants of [Medicago sativa] by self-pollination and by insect pollination.


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[Note on Medicago lupulina, communicated by Mr. Darwin:—]

``I covered a number of plants with a net (which I know does not injure their seeding), and left others close by uncovered, and these were visited incessantly by bees. I could not compare their relative fertility with accuracy, on account of the easy shedding of the seed; but I gathered 150 not quite ripe pods of both; those from under the net weighed 77 grains, and those visited by the bees weighed 101 grains. No doubt the difference in the weight of the seed would have been considerably greater, as the pod is formed independently of the number of seeds.''

    Footnotes Add

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    f1 4929f.f1
    The date range is established by the relationship between this letter and the letters from George Henslow, 1 November 1865 and 6 November 1865.
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    f2 4929f.f2
    CD reported these observations of Medicago lupulina in response to a request from Henslow, who had noted an `irritability in the stamens' of M. sativa that seemed to facilitate cross-pollination by insects (see letter from George Henslow, 1 November 1865 and nn. 5--9, and G. Henslow 1865). CD's observations were also published in Cross and self fertilisation, p. 368. CD's notes on M. lupulina, dated 1859, are in DAR 157a: 45.
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    f3 4929f.f3
    CD's original letter to Henslow has not been found; it evidently contained recommendations of several published works, and possibly information on other Leguminosae (see letter from George Henslow, 6 November 1865 and nn. 3 and 6). Observations made by `Mr. Darwin and others in Trifolium, Lupinus, Phaseolus, &c.', are cited in G. Henslow 1865, p. 329. CD's notes on cross-pollination by insects in Trifolium, Phaseolus, and other leguminous plants, made between 1857 and 1859, are in DAR 157a: 33--8 and 45--8.
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