To Mary Treat 1 January 1873
Down, | Beckenham, Kent.
Jan 1. 73
I am very much obliged for your kind letter;1 & should esteem it a great favour if during warm weather next summer you will observe two points for me in Drosera Filiformis.2 Namely to place some flies within quarter of an inch of the apex of the leaf & observe whether it bends at all after an interval of a day or two. Secondly to rub with a clean needle a few of the glands with some little force, and to touch each gland half a dozen times; & then observe whether in the course of an hour or two the hairs or filaments bearing these glands become incurved. I am glad to hear that D. filiformis catches only small insects, as I suspected this. I have observed with care several other species of Drosera.3 Does the Dionæa4 grow in your neighbourhood? If so I much wish to learn what sort of insects it commonly catches, more especially whether large or small kinds. I have sometimes suspected that its structure & movements favour the escape of small insects.
Dr. Gray has given a rather free translation of what I said to him about nerves; and this related only to Drosera.5 I have found that by pricking a particular point in the leaf I can paralyse half of it; but I must make many more trials next summer before coming to any final conclusion.
With my best thanks | I remain Dear Madam | Yours very faithfully | Charles Darwin
P.S. I subscribe to the American Naturalist, so I am glad to say that I shall see your article—6
Asks for certain observations to be made on Drosera and Dionaea.
Please cite as
Darwin Correspondence Project, “Letter no. 8719,” accessed on 21 October 2016, http://www.darwinproject.ac.uk/DCP-LETT-8719