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Darwin Correspondence Project

To J. D. Hooker   15 [October 1861]

Down Bromley Kent

15th

My dear Hooker

If your Acropera case shd. really turn out as you suspect, it would be very curious & would greatly interest me,—especially, as I chanced in another case to speculate on the possibility of such action. Unless wind by agitating slightly the flower would effect this, I shd. not believe in it. Wind is, necessary to self fertilisation of Bee Ophrys.—1 I hope you will look to this. Try, if by any chance by pricking inside of Labellum, whether it be irritable.— How I shd. like to see one of the Bulbophyllum or other orchids with irritable Labellum!

I shall be particularly glad to see Acropera, as you kindly propose to send it. From analogy with Epipactis palustris, I shd. suspect its use was to direct insects in & out of flower in a different direction.—2

I have seen Odontoglossum & Miltonia: & as you say they have nothing remarkable; except indeed that in Miltonia the caudicle has not usual movements of depression. By the way the mechanism of this movement is rather curious & all lies in the bit of exterior membrane of rostellum, which is removed with gland. It is rather odd that I have not found one accurate or intelligible description of the so-called gland in Ophreæ, & still less in the Vandeæ

Catasetum is too long a story, & would weary you, though it is a pleasure to me to write. You may rely that the ejection of pollinia is special contrivance; & the plant would never set a seed without it; for an insect could never remove pollinia without this action.3 Mr Smith is very partially right about the kind of Elasticity.4 The irritation which excites the rupture of rostellum (this rupturing is common to many Orchids) is transmitted along the curled horns, or as I think I shall call them the antennæ. The pollinia are ejected with sticky gland foremost & will surely stick on the head of insect, when it touches tips of the antennæ, which stand over, what seems to be the nectar-receptacle.—

Ever yours | C. Darwin

[HAND] You must let me send Parslow for a Mormodes when open.— I am very curious to see it5

P.S. I have again changed my mind & shd. be much obliged for 2 or 3 very young buds of any of the Vandeæ   Oncidium wd be best: for I want to see whether the attachment of caudicle is effected in them as in Spiranthes: if you can send me buds, please do not send them for a week, when I shall have finished with Mr Sowerby & drawings.—6

Could you lend me Reichenbach;7 I shd be very glad to see it; if so please send it by enclosed address.—

You speak of pollen-masses of Acropera not sticking to stigma; this is often or generally the case if you pull straight out of stigma; but if you pull at right angles, as an insect could do in flying away, the elastic part of caudicle is stretched & drawn over the edge of stigmatic cavity, & (though so wonderfully strong in some cases) ruptures.

Most cordial thanks for all your kindness & writing so long a letter. I am glad to hear of your Arctic paper.8

Your affect | C. D.

Footnotes

Hooker had apparently examined the parts of an Acropera flower at Kew and noted the unusual structure of the labellum (see letter to J. D. Hooker, 18 October [1861]). CD discussed Acropera in Orchids, stating: ‘this genus for a long time remained the opprobrium of my work. All the parts seemed determinately contrived that the plant should never be fertilised.’ (Orchids, p. 203).
CD refers to the labellum of Acropera (see letter to J. D. Hooker, 18 October [1861]). In Orchids, he called this part ‘an extraordinary organ, baffling description’ and stated that the two upper petals served as ‘lateral guides leading into the hood-like upper sepal’ (Orchids, pp. 204–5).
CD devoted an entire chapter in Orchids to a description of the mechanism by which the pollinia were ejected in Catasetum, which he called ‘the most remarkable of all Orchids’ (Orchids, pp. 211–48).
John Smith was foreman and curator at the Royal Botanic Gardens, Kew (Allan 1967).
These two sentences are written along the left margin of the page. Joseph Parslow was the butler at Down House.
George Brettingham Sowerby Jr was preparing the illustrations for Orchids (see letter to W. E. Darwin, 12 October [1861]).
Hooker 1861.

Bibliography

Allan, Mea. 1967. The Hookers of Kew, 1785–1911. London: Michael Joseph.

Orchids: On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing. By Charles Darwin. London: John Murray. 1862.

Reichenbach, Heinrich Gustav. 1852. De pollinis orchidearum genesi ac structura et de orchideis in artem ac systema redigendis. Leipzig: F. Hofmeister.

Summary

Orchid anatomy. Wind as agent of self-fertilisation in orchids.

Letter details

Letter no.
DCP-LETT-3286
From
Charles Robert Darwin
To
Joseph Dalton Hooker
Sent from
Down
Source of text
DAR 115: 119
Physical description
6pp

Please cite as

Darwin Correspondence Project, “Letter no. 3286,” accessed on 6 April 2020, https://www.darwinproject.ac.uk/letter/DCP-LETT-3286.xml

Also published in The Correspondence of Charles Darwin, vol. 9

letter