To J. D. Hooker   25 [June 1863]

Down Bromley Kent.

25th

My dear Hooker

I have been observing, pretty carefully, a little fact which has surprised me; & I want to know from you & Oliver1 whether it seems new or odd to you; so just tell me whenever you write: it is very trifling fact so do not think of answering on purpose   I have got a plant of Echinocystis lobata to observe the irritability of tendrils described by Asa Gray, & which, of course, is plain enough.2 Having the plant in my study I have been surprised to find that the uppermost part of each branch, (ie the stem between the two uppermost leaves, excluding the growing tip) is constantly and slowly twisting round, making a circle in from 112 to 2 hours: it will sometimes go round 2 or 3 times, & then at same rate untwists & twists in opposite direction. It generally rests half an hour before it retrogrades. The stem does not become permanently twisted. The stem beneath the twisting portion does not move in the least, though not tied. The movement goes on all day & all early night— It has no relation to light for the plant stands in my window & twists from the light just as quickly as towards it.—3

This may be common phenomenon for what I know; but it confounded me quite when I began to observe the irritability of the tendrils.— I do not say it is final cause, but the result is pretty for the plant every 112 or 2 hours sweeps a circle, (according to length of bending shoot & length of tendril) of from 1 foot to 20 inches in diameter, & immediately that the tendril touches any object its sensitiveness causes it immediately to seize it. A clever gardener, my neighbour,4 who saw the plant on my table last night, said “I believe, Sir, the tendrils can see, for wherever I put the plant, it finds out any stick near enough”. I believe the above is the explanation, viz that it sweeps slowly round & round. The tendrils, have some sense, for they do not grasp each other when young.—

Yours affect | C. Darwin

Endorsement: ‘June/63’

2
CD refers to A. Gray 1858b, in which Asa Gray sought to corroborate from his own observations Hugo von Mohl’s suggestion, first made in Mohl 1827, that the coiling of tendrils resulted from their being sensitive to touch. CD’s annotated copy of the volume of the Proceedings of the American Academy of Arts and Sciences in which this paper appeared is in the Darwin Library–CUL. CD reread the article at the end of 1862, with the intention of trying ‘a few experiments’ on the subject, and Gray sent him seeds of Echinocystis lobata for this purpose (see Correspondence vol. 10, letter to Asa Gray, 6 November [1862], and letter from Asa Gray, 24 November 1862). CD’s notes on his experiments with this species, dated 16 June – 29 July 1863, are in DAR 157.2: 29–51.
3
In his Autobiography, p. 129, CD recalled that it was Gray’s paper that led him to take up the subject of climbing plants more generally, and stated: He sent me seeds, and on raising some plants I was so much fascinated and perplexed by the revolving movements of the tendrils and stems, which movements are really very simple, though appearing at first very complex, that I procured various other kinds of Climbing Plants, and studied the whole subject. CD carried out numerous experiments on this subject in 1863 and 1864, and his paper entitled ‘On the movements and habits of climbing plants’ was read before the Linnean Society on 2 February 1865; his observations on Echinocystis lobata are given in ‘Climbing plants’, pp. 74–7. See also the observational and experimental notes in DAR 157.1 and 157.2.
4
The reference is probably to John Horwood, gardener to CD’s neighbour, George Henry Turnbull. Horwood had assisted CD with his botanical experiments over several years (see Correspondence vols. 9 and 10), and, earlier in 1863, had supervised the construction of CD’s hothouse (see letter to G. H. Turnbull, [16? February 1863], and Appendix VI).

Manuscript Alterations and Comments

1.3 it is … purpose 1.4] interl
1.7 stem] above del ‘upper space’
1.8 and] above del ‘the stem’
1.10 It generally … retrogrades.] interl
1.11 does] ‘do’ over ‘is’
2.5 the] over ‘it’
2.5 tendril] interl
2.8 it] above del ‘they’
2.8 finds] altered from ‘find’

Please cite as “DCP-LETT-4221,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-4221