To Daniel Oliver   27 [September 1860]¹

My dear Sir

Your note of 25^th about the gum has been a great relief to me; for I took a panic, as I know I am very apt to blunder & run away with things. After writing to you I looked through my notes, & found I had been rather more careful, than I thought for I had tried 27 leaves with non-nitrogenised substances, not counting saline solutions & simple water. The more I reflect on the experiments which I have tried the less I think I am mistaken. Thus I fully expected that 1 gr of gelatine to oz. of distilled water, would have affected the leaves, but it produced no effect, whereas a little stronger solution produced a marked effect, & whereas 1 gr to 1 oz of several salts with nitrogen produced strong effect.—   Thick syrup on 5 growing leaves produced no effect, whereas a leaf gathered & put into the same solution suffered in extraordinary degree from exosmose & the the hairs & disc of leaf collapsed; so that the vital power seems to resist exosmose in the living plant. I think I have made out the simple mechanism of movement.—   But why I trouble you with all these details I know not.—

I will give you no more trouble, except that I earnestly hope you will try again the old gum; & if it acts, endeavour to find out certainly its composition. Thank you for the pretty leaf of the Australian Drosera; & for paper with gum; but I have a horrid cold & must stop to another day to try it: a large drop or $\frac{1}{2}$ spoon-full dried & then put on heated knife is proper way to try.—

M. Trecul (I am so much obliged to you for telling me of that paper)² disbelieves in any movement & accounts for flies being caught by their crawling under the gumy incurved hairs! But he kept the plants in a green-house or hot-house. Could this have paralysed them? I suppose not: anyhow hot-sunshine seems to make them act better. I imagine he looked out for sudden movement. Vapour of Chloroform for 30 seconds paralyses them completely.—

Thank you much for details of the unnamed Australian species. I will with permission quote your observations.³ Neither D. spathulata or the other species or D. longifolia seem to move quicker than D. rotundifolia.—

I am very glad to hear that you intend to attack spiny plants. Your note shows that it is a complex problem.—⁴

With many thanks. My dear Sir | Yours sincerely | C. Darwin

I have just received a cargo by Post of living plants of Drosera from Down & I will try more gum & starch myself.—⁵

In the unnamed Australian Drosera the incurvation of the leaf itself was terminal I suppose by your sketch. In D. rotundifolia, sometimes the incurvation is terminal; sometimes lateral; & sometimes termino-lateral, so as to be quite variable: as far as I saw in D. longifolia it was always terminal