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Darwin Correspondence Project

From Jeffries Wyman   22 September 1865

Cambridge [Massachusetts]

Sept 22 1865

My Dear Sir

Through the kindness of Dr Gray I have had an opportunity of reading your admirable paper on twining plants, which is so full of admirable observations on vegetable motions.1 These are all of great interest on account of their physiological import, & I have always believed that they were the result of contractility of cells, analogous to those of the lowest animals.2 Not however because this contractility has been actually demonstrated, but because it is the most reasonable to suppose that it exists. The movements of stems, but especially of petioles or tendrils, on the application of an irritation, are so analogous to those of some of the lower animals, that if one were not prepossessed with the idea that the motions of plants & animals could not be alike, we should at once admit their likeness. However I do not propose to discuss the question, but only to mention an experiment which gives a mechanical explanation of the double spiral of tendrils after the free end has become attached. The experiment shows, that if the cells on one side of a tendril were to shorten, & this in a straight line, the tendril (its ends being fixed to moveable supports) would at once assume the form of a double spiral.3

Take a piece of elastic cord (a) 3 inches long & a piece of twine (b) of the same size, 4 or 5 inches long, & tie their two ends together—

[DIAG HERE]

Stretch the elastic cord until the two are of the same length & secure them in this condition by fastening the ends, taking care that the two are exactly parallel & in contact. Wind both with fine thread, closely. In this way we have a compound cord contractile (through the elasticity of the india rubber) on one side & passive on the other. Hold the ends of this cord between the fingers, stretch it to its full length, & then allow the two ends to approach each other slowly. The cord at once begins to assume the form of a double spiral exactly reproducing the form of the tendril.

I do not find that the mathematicians can give an analysis of this motion, at any rate did not when asked what it ought to be a priori, & have not after they have seen it. Of course they will make it out, but the problem is not an easy one. I hope you will excuse me for troubling you with this, for although the experiment illustrates the spirals of the tendril & shows how they might be made it does not prove how the actually are made.

With great respect | Sincerely yours | J Wyman

Charles Darwin Esq

Footnotes

CD had sent a copy of ‘Climbing plants’ to Asa Gray, who evidently lent it to Wyman (see letter to Asa Gray, 19 April [1865]).
For Wyman’s views on contractility in plant cells, see Wyman 1854.
CD had attempted to explain the bi-directionality of the spirals of caught tendrils in ‘Climbing plants’, pp. 95–8. Gray suggested that CD might have explained the phenomenon simply as a mechanical necessity (see letter from Asa Gray, 24 July 1865 and n. 6); however, CD maintained that his explanation was necessary because the phenomenon was not easy to understand (see letter to Asa Gray 15 August [1865] and n. 4). CD did not alter this section in the second edition of Climbing plants (see pp. 163–9).

Bibliography

Climbing plants: On the movements and habits of climbing plants. By Charles Darwin. London: Longman, Green, Longman, Roberts & Green; Williams & Norgate. 1865.

‘Climbing plants’: On the movements and habits of climbing plants. By Charles Darwin. [Read 2 February 1865.] Journal of the Linnean Society (Botany) 9 (1867): 1–118.

Wyman, Jeffries. 1854. [Cause of contractility in some vegetable tissues.] [Read 8 November 1854.] Proceedings of the American Academy of Arts and Sciences 3 (1852–7): 167–8.

Summary

Discusses the climbing movements of plants and describes experiment to establish a mechanical explanation for double spiralling movements of tendrils.

Letter details

Letter no.
DCP-LETT-4897
From
Jeffries Wyman
To
Charles Robert Darwin
Sent from
Cambridge Mass.
Source of text
DAR 181: 190
Physical description
4pp

Please cite as

Darwin Correspondence Project, “Letter no. 4897,” accessed on 19 October 2019, https://www.darwinproject.ac.uk/letter/DCP-LETT-4897.xml

Also published in The Correspondence of Charles Darwin, vol. 13

letter