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Darwin Correspondence Project

To J. S. Burdon Sanderson   15 August 1873

Bassett Southampton

Aug 15. 1873

My dear Dr Sanderson

I am much obliged for your letter which has been forwarded to me here—but I return home next Thursday—1 I assure you I felt quite guilty when I read in the Times your grand address on Physiology, at the thought that I had troubled you, at such a time, with my queries.2

I quite understand what you say about heat rigor.3

I shd think that it wd be extremely interesting to ascertain whether there is any electrical change in the leaves of Drosera when they are excited; but I shd think Dionæa wd be much better for the purpose. As far as I can imperfectly make out the lower surface of the leaf in Dionæa, & of the tentacles (i.e prolongations of the leaf) of Drosera is always in a state of tension, but is over mastered by the contraction of the upper surface alone—4

Therefore I imagine that the upper & lower surface wd exhibit an electrical change (if such there be) during the act of inflection   Now Dionæa, from the large size of the leaf & from the suddenness & greatness of the movement, wd be the best to operate on. If on further reflection you are willing to investigate this point, I wd gladly send you by a servant plants in good condition, for I suppose you wd require to have the plants at the Institute & not at Down—5

If you obtained any result, it seems to me that it wd be a remarkable discovery & well worth your publishing.—6

I had thought that it might be worth while to test Dionæa during inflection by the thermo-electric pile. A common thermometer gave no indication of any rise of temperature, so that it seems very doubtful whether the experiment wd be worth trying.7 If you find you have time & inclination to examine Dionæa or Drosera under the foregoing point of view, please to let me hear—

With many thanks yours very sincerely— | Charles Darwin


See letter from J. S. Burdon Sanderson, 13 August [1873]. CD stayed in Bassett, Southampton, from 9 to 21 August 1873 (see ‘Journal’ (Appendix II)).
Burdon Sanderson’s address on physiology, delivered to the Congress of the British Medical Association on 8 August 1873, was reported in detail in The Times, 9 August 1873, p. 10.
Drosera is the genus of sundews; Dionaea is a monospecific genus whose only species is Dionaea muscipula, the Venus fly trap. For Burdon Sanderson’s experiments on Dionaea, see the letter from J. S. Burdon Sanderson, 13 August [1873] and n. 7.
Burdon Sanderson was appointed the first superintendent of the Brown Animal Sanatory Institution in 1872 (G. Wilson 1979, p. 172).
Burdon Sanderson did not experiment with a thermopile (a device that converts thermal energy into electrical), but used a galvanometer (a device for detecting and measuring electric current) to record the nerve-like response of a leaf of Dionaea when stimulated with an induction coil (see Burdon Sanderson 1874, p. 128).


Thinks it would be worth while testing for electrical changes in the leaves of insectivorous plants.

Please cite as

Darwin Correspondence Project, “Letter no. 9013,” accessed on 15 December 2017,

Also published in The Correspondence of Charles Darwin, vol. 21