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Darwin Correspondence Project

To J. D. Hooker   7 June [1860]

Down Bromley Kent

June 7th

My dear Hooker

Best & most beloved of men, I supplicate & entreat you to observe one point for me. Remember that the Goodeniaceæ have weighed like an incubus for years on my soul.—1 It relates to Scævola microcarpa. I find that in bud the indusium collects all the pollen splendidly, but differently from Leschenaultia cannot be afterwards easily opened.2 Further I find that at early stage, when flower first opens a boat-shaped stigma lies at bottom of indusium; & further that this stigma after flower sometime expanded grows very rapidly, when plant is kept hot, & pushes out of indusium a mass of pollen & at same time two horns project at corners of the indusium; now the appearance of these horns makes me suppose that these are the stigmatic surfaces. Will you look to this? for if they be, you will see by relative position of parts, with indusium & stigmas bent at right angles to style, that an insect entering a flower could not fail to have whole back (at the period when as I have seen, a whole mass of pollen is pushed out) covered with pollen which would almost certainly get rubbed on the two horns.—

Indeed I doubt whether, without this aid whether pollen would get on to the horns.—   What interests me in this case is the analogy in result with Lobelia but by very different means. In Lobelia the stigma before it is mature pushes by its circular brush of hairs the pollen out of conjoined anthers; here the indusium collects pollen & then the growth of stigma pushes it out.— In course of about 112 hour, I found an indusium with hairs on outer edge perfectly clogged with pollen, & horns protruded, which before the 112 hour had not one grain of pollen outside the indusium. & no trace of protruding horns. So you will see how I wish to know whether the horns are the true stigmatic surfaces.—   I could try the case experimentally by putting pollen on the horns, but my greenhouse is so cold & my plant so small & in such little pot, that I suppose it would not seed.—

Forgive me.—   Your affect | C. Darwin

Etty is rather decidedly better today & we are all in jolly spirits.3

The little length of stigmatic horns at the moment when pollen is forced out of indusium, compared to what they ultimately attain, makes me fancy that they are not then mature or ready & if so, as in Lobelia, each flower must be fertilised by pollen from another & earlier flower. How curious that indusium shd. first so cleverly collect pollen & then afterwards push it out! Yet how closely analogous the Campanulas brushing pollen out of the anthers & retaining it on hairs till stigma is ready.— I am going to try whether Campanula sets seeds without insect-agency.—

Footnotes

The Goodeniaceae apparently contradicted CD’s belief that all organic beings must occasionally cross-fertilise. He had referred to the problem in his ‘big book’ on species (Natural selection, pp. 63–4), explaining how the pollen and stigma in Goodenia were completely enclosed by an indusium in the flower. He had subsequently studied the structure of the related genus Leschenaultia (see letters to J. D. Hooker, [26 February or 4 March 1860], 12 March [1860], and 7 May [1860]).
CD’s observations and experiments on Scaevola and Leschenaultia are recorded in his Experimental book (DAR 157a). The observations described in the letter are dated 1 June 1860 (Experimental book, p. 64).
Henrietta Emma Darwin had been ill since the end of April 1860.

Summary

Floral anatomy of Goodeniaceae: although flowers seem to fertilise themselves by pistil moving to anther, CD shows that insect agency is necessary. Wants JDH to check his interpretation of stigmatic surface.

Letter details

Letter no.
DCP-LETT-2823
From
Charles Robert Darwin
To
Joseph Dalton Hooker
Sent from
Down
Source of text
DAR 115: 61
Physical description
6pp

Please cite as

Darwin Correspondence Project, “Letter no. 2823,” accessed on 17 December 2017, http://www.darwinproject.ac.uk/DCP-LETT-2823

Also published in The Correspondence of Charles Darwin, vol. 8

letter