To J. D. Hooker   4 July 1874

My dear Hooker

I do not know that I have any suggestion beyond that in my last note; but it w^d be very interesting to prove that some plants feed on decayed animal matter, whilst others, like Drosera &c, can digest fresh animal matter.¹ If I was working on Nepenthes, I sh^d first try, by suspending cubes of albumen & meat, (of about $\frac{1}{10}$ inch) in the fluid (some being allowed to touch the bottom) & if, after 48 hours, the angles were not rounded, I sh^d try for the products of animal decomposition. To do this I w^d empty the fluid out of the pitchers & fill one with a sol. of citrate of ammonia & another with nitrate of amm. of the strength of 1 grain to 2 or 3 oz of water. I sh^d select these salts because I think citric acid is in the fluid (& this may be its use;) & the nitrate is the ultimate product of decomposition. I sh^d then look, after 24 hours, for aggregation of the protoplasm in the glands; as I know that these salts thus act.

The phosphate of ammonia w^d also be good for trial. If these salts cause aggregation, I w^d certainly get a chemist to test the fluid with old rotten insects for salts of ammonia.

Your fact about the nectar on the lid is very interesting:² I w^d suggest, from what I have actually seen with other plants, to place a plant of nepenthes, the lid of which had no nectar on it, in bright sunshine for an hour or two, (if the plant w^d stand so much exposure) & see if nectar is not at once secreted. I hope that the lid of Nepenthes is brightly coloured, as with Saracenia, so as to attract insects by sight.

I am very glad you have written about Utricularia, for this mg a second source has failed me.³

I long to see you here again—⁴ | yours affectionately | Ch. Darwin