To J. S. Burdon Sanderson   15 August 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 sh^d think that it w^d be extremely interesting to ascertain whether there is any electrical change in the leaves of Drosera when they are excited; but I sh^d think Dionæa w^d 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 w^d 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, w^d be the best to operate on. If on further reflection you are willing to investigate this point, I w^d gladly send you by a servant plants in good condition, for I suppose you w^d require to have the plants at the Institute & not at Down—⁵

If you obtained any result, it seems to me that it w^d 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 w^d 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