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Darwin Correspondence Project

To J. D. Hooker   6 September [1860]1

Down Bromley Kent

Sept 6th

My dear Hooker

I was surprised & pleased to get your last note; for I did not at all expect another.—2 We were amused at your original views on insanity.—   My Father thought something the same; at least he thought almost everyone was insane on some point. Thank you much for thinking about Asses & Mules: the forked stripe on shoulder is a very curious point (& I have seen traces of it) for the meaning of the fork is plain when the legs are transversely barred, but is an absurdity (except on doctrine of inheritance) with an animal with unstriped legs.—3 If you go up lofty mountains compare general state of vigour of the first individuals of any species of plant, which you meet, with the last, with respect to struggle for life, as alluded to in Origin—;4 also the degree of abruptness of limitation of the species.—

The rest of this letter I write to amuse myself & not for your sake, as I have a weakness, that I can never enjoy my work, till I have told you.— You are my public.—   But before I begin, I must say how entirely agree about the detestable article in Athenæum about Tyndall—sneering at his veracity—& very disagreeable about Huxley.—5 I look at the Editor as a spiteful old woman, who has taken, what my Brother calls her D.B. degree (ie damned bitch)—6

With respect to Drosera, there is no doubt that the plant is acute enough & knows what is good. It releases from its gripe an inorganic body far sooner than an organic body. But fluids show the difference better than the act of mere releasing. I have tried only the following 14 fluids, made as nearly as possible the same thin consistency, & in most case each fluid on several leaves. Water, syrup of sugar, starch, gum, olive-oil—sherry wine, carbonate of soda; these contain no nitrogen & never cause any inflection of the leaves or hairs. On other hand, milk cold infusion of raw meat, urine, raw white of egg, thin gelatine, thin mucus from lungs, & saliva all cause most powerful contraction & all contain nitrogen.—   Saliva contains less than one percent of animal matter. But here comes the really curious case, a solution in proportion of 1 grain of Carbonate of Ammonia to 1 oz of water (ie 1 to 480 parts by weight) & of this solution 12 minim being taken, positively & certainly produces great effect. Hence 1960 of one grain of C. of Ammonia causes contraction. This evening I rerepeated experiment on 5 leaves (on some of which I had put drop of distilled water in morning with no effect) & all are now contracted. Is this not curious? Nor am I got to minimum strength of solution yet.—7

I daresay you had no time to read my note of action of rostellum in Malaxis & Epipactis.8 I have now examined Spiranthes autumnalis (for God’s sake if you find any odd genus of Orchis if you can, put it in weak spirits with buds & old flowers for me, for I am fairly mad on subject) & in Spiranthes we have new & curious modification, which I must publish to you my public.9 Within the rostellum, there is formed a hard canoe-shaped object; placed vertically, ie parallel to axis of flower; diagram the anthers shrivel & leave pollinia lying at back of rostellum (as in Listera) in bud, & the rostellum splits behind, & the pollinia become permanently attached to the now naked bottom of “canoe”. Now the flower opens. If you then touch most delicately the rostellum in front (ie on side over the stigmatic surface,) the external membrane by a vital action instantly splits longitudinally down its whole length, & exposes the open part of canoe, which canoe is filled with extremely viscid matter; & this viscid matter sets instantly hard (as in Listera), so that the touching object—(a bristle or probosis of insect) is glued firmly to the “canoe” & this being already glued to the pollinia, all are withdrawn together. The rostellum then presents a split appearance. The membranous edges of the now split rostellum form the two foliaceous projections to the rostellum described by some authors!10 If you can understand this, you will think it is cerious modification of the Listera type of structure.

Farewell my dear Hooker. Do take care of yourself.—   I am very glad your family approve of your Expedition.11 It is wonderfully spirited.

Farewell    may you prosper | Yours affectionately | C. Darwin

I have written all this for my enjoyment & not a bit for yours.—


Dated by the reference to Hooker’s forthcoming expedition to Syria (see n. 11, below).
Neither of the letters Hooker wrote to CD before his departure for Syria has been found. See also letter to J. D. Hooker, 2 September [1860].
CD asked Hooker to look out for asses with shoulder- or leg-stripes during his trip to Syria (letter to J. D. Hooker, 2 September [1860]). Hooker observed five asses in Syria in which the shoulder-stripe was ‘plainly forked over the fore leg.’ ( Variation 1: 63).
Origin, p. 69.
The Athenæum, 1 September 1860, pp. 280–2, carried an anonymous review of John Tyndall’s Glaciers of the Alps (Tyndall 1860). The book described some of Tyndall’s alpine climbs, on one of which he was accompanied by Thomas Henry Huxley. The reviewer wrote in such a way as to make the climbers‘ attempts seem foolish.
The editor of the Athenæum was William Hepworth Dixon. See also letter to Asa Gray, 22 July [1860]. CD refers to Erasmus Alvey Darwin.
CD performed a series of experiments on Drosera after returning to Down from Hartfield on 2 August and before leaving for Eastbourne on 22 September. His notes are in DAR 60.1.
CD probably refers to the ‘abstract’ mentioned in the letter to J. D. Hooker, 7 August [1860].
The Spiranthes autumnalis had been supplied by Alexander Goodman More (see letter to A. G. More, 5 September [1860]).
CD refers to Hooker’s paper on the structure of Listera ovata (Hooker 1854b). The similarities between the fertilisation of this species and of S. autumnalis are discussed in Orchids, p. 151.
Hooker left England for Smyrna (Izmir), Turkey, on 15 September 1860. He returned in mid-November (L. Huxley ed. 1918, 1: 528).


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.

Origin: On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life. By Charles Darwin. London: John Murray. 1859.

Tyndall, John. 1860. The glaciers of the Alps. Being a narrative of excursions and ascents, an account of the origin and phenomena of glaciers, and an exposition of the physical principles to which they are related. London: J. Murray.

Variation: The variation of animals and plants under domestication. By Charles Darwin. 2 vols. London: John Murray. 1868.


Thanks JDH for agreeing to observe coats of asses and mules in Middle East.

Asks for observations on vigour of plants as JDH ascends mountains.

Ad hominem article in Athenæum [review of John Tyndall, Glaciers of the Alps, 1 Sept 1860, pp. 280–2].

Reports extensive experiments on Drosera.

Observations on orchid anatomy.

Letter details

Letter no.
Charles Robert Darwin
Joseph Dalton Hooker
Sent from
Source of text
DAR 115: 74
Physical description
ALS 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 2908,” accessed on 30 November 2023,

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