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Letter 5050

Darwin, C. R. to Müller, J. F. T.

[9 and] 15 Apr [1866]

    Summary Add

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    Structure of Scaevola and its fertilisation with insect aid.

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    Fertilisation of Aristolochia.

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    FM's paper on climbing plants [see 5146].

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    Is preparing new edition of Origin.

Transcription

Down. | Bromley. | Kent. S.E.

April 15th.

My dear Sir,

I am very much obliged by your letter of February the 13th abounding with so many highly interesting facts. Your account of the Rubiaceous plant is one of the most extraordinary that I have ever read, and I am glad you are going to publish it. I have long wished some one to observe the fertilization of Scævola, and you must permit me to tell you what I have observed: First for the allied genus of Leschenaultia: utterly disbelieving that it fertilizes itself, I introduced a camel-hair brush into the flower in the same way as a bee would enter, and I found that the flowers were thus fertilized, which never otherwise happens; I then searched for the stigma, and found it outside the indusium with the pollen tubes penetrating it: and I convinced Dr Hooker that botanists were quite wrong in supposing that the stigma lay inside the indusium. In Scævola microcarpa the structure is very different, for the immature stigma lies at the base within the indusium; and as the stigma grows it pushes the pollen out of the indusium and it then clings to the hairs which fringe the lips of the indusium; and when an insect enters the flower, the pollen (as I have seen) is swept from these long hairs onto the insect's back. The stigma continues to grow, but is not apparently ready for impregnation until it is developed into two long protruding horns, at which period all the pollen has been pushed out of the indusium. But my observations are here at fault, for I did not observe the penetration of the pollen tubes. the case is almost paralell with that of lobelia. Now I hope you will get two plants of Scævola, and protect one from insects, leaving the other uncovered, and observe the result both in the number of capsules produced, and in the average number of seed in each. It would be well to fertilize half a dozen flowers under the net, to prove that the cover is not injurious to fertility.

With respect to your case of Aristolochia, I think further observation would convince you that it is not fertilized only by larvæ, for in a nearly parallel case of an Arum and an Aristolochia, I found that insects flew from flower to flower. I would suggest to you to observe any cases of flowers which catch insects by their probosces, as occurs with some of the Apocyneæ, I have never been able to conceive for what purpose (if any) this is effected; at the same time, if I tempt you to neglect your Zoological work for these miscellaneous observations I shall be guilty of a great crime

To return for a moment to the indusium; how curious it is that the pollen should be thus collected in a special receptacle, afterwards to be swept out by insects' agency!

I am surprised at what you tell me about the fewness of the flowers of your native Orchids which produce seed-capsules. What a contrast with our temperate European species with the exception of some sp. of Ophrys!— I now know of 3 or 4 cases of self-fertilising orchids; but all these are provided with means for an occasional cross.— I am sorry to say Dr. Crüger is dead from a fever.—

I received yesterday your paper in Bot. Zeitung on the wood of Climbing Plants: I have read as yet only your very interesting & curious remarks on the subject as bearing on the change of species; you have pleased me by the very high compliment which you pay to my paper.—

I have been at work since March 1st on a new English Edition of my Origin, of which when published I will send you a copy. I have much regretted the time it has cost me, as it has stopped my other work. On the other hand it will be useful for a new 3d German Edition which is now wanted. I have corrected it largely & added some discussions, but not nearly so much as I wished to do, for being able to work only two hours daily, I found I shd. never get it finished.— I have taken some facts & views from your work ``Fur Darwin''; but not one quarter of what I shd. have liked to have quoted.

With the more cordial respect & thanks, Believe me my dear Sir Yours most sincerely | Ch. Darwin

    Footnotes Add

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    f1 5050.f1
    The year is established by the reference to the letter from Fritz Müller, 13 February 1866. The original date of `9th' was crossed out and `15th.' written below.
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    f2 5050.f2
    See letter from Fritz Müller, 13 February 1866.
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    f3 5050.f3
    The discussion of the rubiaceous plant was evidently in a missing portion of Müller's letter of 13 February 1866. Müller described the plant in the 27 April 1866 issue of Botanische Zeitung (F. Müller 1866a). Uncertain whether the plant was a species of Posoqueria, Müller named it Martha (posoqueria?) fragrans. The species is now known as Posoqueria densiflora. In Forms of flowers, p. 131 n., and Cross and self fertilisation, pp. 5, 391, CD mentioned `Posoqueria fragrans', as described by Müller, among plants in which special movements of certain floral organs ensure cross-pollination.
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    f4 5050.f4
    In his letter of 5 November 1865 (Correspondence vol. 13), Müller had mentioned a Scaevola growing on the east coast of the island of Santa Catarina, Brazil. CD began experiments with another member of the Goodeniaceae, Leschenaultia, in April 1860 (see Correspondence vol. 8). His initial results were reported in the letter to the Journal of Horticulture, [17 May 1861] (Correspondence vol. 9). CD's notes on pollination in Leschenaultia are in in his Experimental notebook (DAR 157a), and DAR 265.
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    f5 5050.f5
    CD discussed Leschenaultia in 1860 with Joseph Dalton Hooker, who disagreed with CD's view that the stigma was outside the indusium (see Correspondence vol. 8, letter to J. D. Hooker, 18 April [1860], and letter from J. D. Hooker, [28 April 1860]). In 1862, CD made further observations that confirmed his view; these were corroborated by Hooker (see Correspondence vol. 10, letter from J. D. Hooker, [16 May 1862]). CD later published an account of his observations in a letter to the Gardeners' Chronicle, [before 9 September 1871] (Calendar no. 7926; Collected papers 2: 162--5).
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    f6 5050.f6
    CD described pollination in Scaevola microcarpa, noting its analogy with Lobelia, in a letter to J. D. Hooker, 7 June [1860] (Correspondence vol. 8). His notes on Scaevola are in his Experimental notebook (DAR 157a). CD discussed the cross-pollination mechanism of Lobelia in Origin, pp. 98--9, and Cross and self fertilisation, p. 176. See also Correspondence vol. 6, letter to Asa Gray, 5 September [1857]. CD's notes on Lobelia are in DAR 49: 85, 88, 88v. It appears in a list of plants, `apparently adapted to prevent self fertilization', in DAR 117: 71. For more on the pollination mechanisms of Scaevola, Leschenaultia, Lobelia, and related genera, see ML 2: 257--9.
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    f7 5050.f7
    Müller was unable to perform the experiments with Scaevola because all his specimens died (Correspondence vol. 15, letter from Fritz Müller, 4 March 1867).
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    f8 5050.f8
    The information on Aristolochia is probably in a missing portion of Müller's letter of 13 February 1866. CD compared Arum maculatum, the filaments of which are constructed so as to trap insects, with Aristolochia in Cross and self fertilisation, pp. 417--18; he reported experiments made in 1842 that indicated that insects were able to escape from Arum maculatum and carry pollen to another plant.
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    f9 5050.f9
    The sub-family Apocyneae (family Apocynaceae) includes the American fly-trap (Apocynum androsaemifolium); it is cross-pollinated by insects, which can become caught by their probosces or legs. CD was familiar with this species (see Correspondence vol. 8, letter to Daniel Oliver, [21 November 1860] and n. 5, and letter from Daniel Oliver, 23 November 1860). The original text has been corrected in CD's hand from `Asclepiadae' to `Apocyneae'; on contemporary disagreements about the inclusion of particular species within these families, see Lindley 1853, p. 625.
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    f10 5050.f10
    The information on orchids was probably in a missing portion of Müller's letter of 13 February 1866.
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    f11 5050.f11
    In Orchids, pp. 358--9, CD had remarked on the rarity of self-pollination among orchids, and stated that only the bee ophrys (Ophrys apifera) had `special and perfectly efficient contrivances' for self-pollination. CD later described a number of other species in which self-pollination regularly occurred, noting that in each case structures were present that enabled the plants to be cross-pollinated by insects (see `Fertilization of orchids', p. 158 (Collected papers 2: 155), and Orchids 2d ed., pp. 291--2).
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    f12 5050.f12
    Hermann Crüger had died in February 1864 (R. Desmond 1994).
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    f13 5050.f13
    CD refers to F. Müller 1866b and to the journal Botanische Zeitung. Müller had enclosed his manuscript of the article in his letter of 10 October 1865 (Correspondence vol. 13), requesting that CD forward it to Max Johann Sigismund Schultze for publication. CD's annotated copy, with a separate sheet of notes in his own hand, is in the Darwin Pamphlet Collection--CUL.
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    f14 5050.f14
    Müller stated that all the woody climbing plants he observed had clefts or fissures in their trunks; he described a Bignonia that had such clefts only in the portion of the plant that climbed, and remarked that such a feature could not have arisen through special creation, but was best explained by CD's theory (F. Müller 1866b, p. 68). In his notes on Müller's paper, CD wrote, `he shows that great majority of Climbers have cleft wood—& that this might easily, being useful (how?) have been acquired through natural selection— On other hand certain great peculiarities do not appear in different Fam, as might have been expected if structure of each had been due to independent creation' (square brackets in original).
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    f15 5050.f15
    In F. Müller 1866b, p. 68, Müller thanked CD for sending him a copy of `Climbing plants', noting that the work had inspired him to make further observations.
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    f16 5050.f16
    Müller's name appears on CD's presentation list for the fourth edition of Origin (see Correspondence vol. 14, Appendix IV).
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    f17 5050.f17
    See letter from E. Schweizerbart'sche Verlagsbuchhandlung, 23 March 1866.
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    f18 5050.f18
    CD refers to F. Müller 1864c. CD had added references to F. Müller 1864c to the fourth edition of Origin. No new references to Müller 1864c were added to the third German edition (Bronn and Carus trans. 1867).
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