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Letter 2116

Darwin, C. R. to Hooker, J. D.

1 July [1857]

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    Summary Add

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    George Henslow's curtness to JDH: "an attack of religion".

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    Embryonic leaves. Adaptive functions and taxonomic significance of cotyledons.

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    Asa Gray. Separation of sexes in U. S. trees.


Down Bromley Kent

July 1st

My dear Hooker

I write to say how truly I think you the best of men for proposing to pay us a visit this summer, I shall most truly & heartily enjoy it. In a few weeks time we shall know our plans better, as Etty & our Boys holidays make everything doubtful I am alone at present Emma visiting some relations with a tail of six children! I am very sorry to hear about G. Henslow: an attack of religion is a most serious thing: the whole affair must be a great disappointment to you.—

Thanks for your interesting note about embryonic leaves: after I had sent it, I began to think about cotyledons, & marvelled that I could not remember having ever read any discussion on their resemblances & dissimilarities in allied plants. How curious that the subject shd never have been taken up! I do not even know whether functions of the cotyledons are same as leaves, or whether they serve, also, as receptacle of nutriment: I have noticed in my weed-garden that their destruction seems always to kill the plant.— I was speculating in my ignorance that the form of cotyledon was probably related to the shape of seed & its embryo & radicle; & if this were so, as seeds are adapted to various contingencies, we might expect the cotyledons to differ; but probably this is not the case, as it wd have occurred to you. I am not learned enough in animal embryology to compare cotyledons with amnios &c &c.—

If cotyledons have a relation to the external conditions of existence distinct or partially different from what the leaves of the mature plant have to the conditions, I think the differences of the cotyledons in the same Family, would be explicable in the same way as in some Diptera & some Neuroptera, there is a wonderful amount of difference in the larvæ:— no doubt these larvæ have much in common, & so I presume the cotyledons have much in common.

I have had another letter from Asa Gray: most kindly he has worked out trees of U. States & finds out of 132, 95 have sexes more or less separate (= .72); so that the Rule seems here to hold good whether or no my explanation is correct.

Farewell | My dear Hooker | Ever yours | C. Darwin

    Footnotes Add

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    f1 2116.f1
    The year is established by the subjects discussed and by CD's reference to Emma Darwin and the children being away from Down (see n. 2, below).
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    f2 2116.f2
    Emma and the children were visiting Francis (Frank) Wedgwood and his family in Barlaston, Staffordshire. They later travelled to Shrewsbury, the children returning to Down on 4 July 1857 and Emma on 6 July (Emma Darwin's diary).
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    f3 2116.f3
    The missing portion of the letter from J. D. Hooker, [27] June 1857 may have discussed this point.
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    f4 2116.f4
    See letter from Asa Gray, 1 June 1857.
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