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Darwin Correspondence Project

To J. D. Hooker   1 May [1862]1

Down.

May 1.

My dear Hooker,

If you can screw out time, do look at stigma of blue Leschenaultia biloba; I have just examined large bud with indusium not yet closed, & it seems to me certain that there is no stigma within.2 The case would be very important for me, & I do not like to trust solely to myself. I have been impregnating flowers, but it is rather difficult. Singular case of highly peculiar structure, now remodified into the functional condition of a Campanula.—3

Ever yours | C. Darwin

How odd it is that pollen shd be enclosed within the indusium & then have to be removed out of it & put on the stigma by insects.

Footnotes

The year is provided by the relationship to the letter from J. D. Hooker, [5 May 1862].
CD began to experiment with Leschenaultia in April 1860 in regard to his work on pollination (see Correspondence vol. 8, letter to J. D. Hooker, 12 March [1860] and n. 1). L. formosa seemed to have an effective mechanism for preventing cross-fertilisation, the pollen being ‘shed in the early bud’ and ‘there shut up round the stigma within a cup or indusium’ (see Correspondence vol. 9, letter to Journal of Horticulture, [17 May 1861]). CD initially suspected that the two viscid surfaces on the outside of the indusium might in fact be stigmatic surfaces, thus requiring insect agency to effect pollination (Correspondence vol. 8, letter to J. D. Hooker, 26 April [1860]), but Hooker had convinced him that the stigma was inside the indusium (Correspondence vol. 8, letter from J. D. Hooker, [28 April 1860]). However, CD carried out further investigations that encouraged him to maintain that pollination involved removal of the pollen from the indusium by insects, thus allowing cross-pollination (see Correspondence vol. 8, and Correspondence vol. 9, letter to Journal of Horticulture, [17 May 1861]). In CD’s Experiment book (DAR 157a), there is a diagram of the indusium in a flower of the blue L. biloba var. splendens, dated 18 April 1862, showing the stigma located externally. CD recorded the observations given here in a note dated 1 May 1862 (DAR 265). CD also attempted to effect pollination in several flowers, but did not succeed until later in the year (see the letter to J. D. Hooker, 11 June [1862], and the notes dated 2 June and 29 October 1862 in DAR 265)). CD subsequently published an account of his observations on L. formosa and L. biloba, made during 1860 and 1862, in a letter to the Gardeners’ Chronicle and Agricultural Gazette, 9 September 1871 (Collected papers 2: 162–5).
In species of Campanula the pollen is shed at an early stage in the maturation of the flower, adhering to collecting hairs that surround the pistil beneath the stigma. As a result the flowers cannot be pollinated without mechanical aid, as CD believed to be the case in Leschenaultia. See Cross and self fertilisation, p. 174.

Summary

Asks JDH to look at stigma of Leschenaultia biloba; it seems certain there is no stigma within the bud. Case would be important.

Singular case of peculiar structure now remodified into the functional condition of a Campanula.

Letter details

Letter no.
DCP-LETT-3529
From
Charles Robert Darwin
To
Joseph Dalton Hooker
Sent from
Down
Source of text
DAR 115: 153
Physical description
2pp

Please cite as

Darwin Correspondence Project, “Letter no. 3529,” accessed on 20 April 2019, http://www.darwinproject.ac.uk/DCP-LETT-3529

Also published in The Correspondence of Charles Darwin, vol. 10

letter