My dear Sir,

I have been much interested by your letter,¹ & thank you for sending it; for as I am working together with my son Francis² on the movements of plants, we like to learn as much as we can about them, tho’ I do not intend to write anything about the mechanism of the movements.

I imagine from your remarks that when an Oscillatoria bends from side to side, you suppose that the movement depends on the opposite walls alternately becoming more extensile, together with the interior of the cells being in a state of turgescence.³ Do you feel sure that the cell walls have not a power of contraction; for I could not avoid suspecting that they had this power, whilst observing the movements of Drosera and Dionæa.⁴ But the subject is a most difficult one and I heartily wish you success in your observations.

My dear Sir | Yours sincerely | Charles Darwin

P.S. | I enclose a few seeds of Lychnis Githago. It is the hypocotyledenous stem not the root which I observed contracting.⁵