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Letter 5059F

Darwin, C. R. to Henslow, George

[before 19 Apr 1866]

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In the Broom, if the flowers be protected from insects, the parts (stamen and pistil) do not spring out, and scarcely any pods are produced. In a flower lately expanded, when a bee alights on the keel, the shorter stamens alone are ejected, and they dust the abdomen of the insect. When the flower is a day or two older, if a bee alights on the keel, the pistil and longer stamens spring violently out, and the hairs on the pistil deposit plenty of pollen on the bee's back, against which the stigma is rubbed. When the bee flies away, the pistil curls still more, and the stigmatic surface becomes up-turned, and stands close to the protruded anthers of the shorter stamens. We have seen that the bee gets dusted in its abdomen from the shorter stamens of the younger flowers; and this pollen will be left on the up-turned stigma of the curled pistil of the older flowers. Thus both the upper and lower surface of the bee gets dusted with pollen, which will be transferred to the stigma at two different periods.

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    f1 5059f.f1
    The date is established by the relationship between this memorandum and the date, 19 April 1866, on which it was read to the Linnean Society as part of Henslow 1866a (see n. 2, below).
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    f2 5059f.f2
    Henslow included this note, `kindly communicated … by Mr. Darwin', in his paper on pollination in Indigofera (Henslow 1866a; see also letter to George Henslow, 16 April [1866] and n. 2). CD was interested in dichogamy in Cytisus scoparius, the common broom, as well as in its mechanism for insect pollination. His notes date from May 1857, and include measurements of stamens of different lengths, and observations of the curling of the pistil, and of bee visits (DAR 76). CD's son, William Erasmus Darwin, also made extensive observations on broom (see letter from W. E. Darwin, 8 May [1866]).
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    f3 5059f.f3
    The original letter has not been found.
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