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Darwin Correspondence Project

To J. D. Hooker   4 July 1874

Down, | Beckenham, Kent.

July 4 1874

My dear Hooker

I do not know that I have any suggestion beyond that in my last note; but it wd 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 shd first try, by suspending cubes of albumen & meat, (of about 110 inch) in the fluid (some being allowed to touch the bottom) & if, after 48 hours, the angles were not rounded, I shd try for the products of animal decomposition. To do this I wd 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 shd 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 shd 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 wd also be good for trial. If these salts cause aggregation, I wd 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 wd 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 wd 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


See letter to J. D. Hooker, 2 July 1874. Hooker had asked for hints for observation on Nepenthes (the tropical pitcher-plant) in his letter of 3 July 1874. Drosera is the genus of sundews.
In his letter of 3 July 1874, Hooker mentioned he had observed a sugary secretion produced by a gland on the undersurface of the lid of the pitcher in Nepenthes.
See letter from J. D. Hooker, 1 July 1874. CD had asked several correspondents for specimens of Utricularia (bladderwort; see letter to W. T. Thiselton-Dyer, 26 June 1874). He probably refers to William Darwin Fox (see letter to John Ralfs, 8 July 1874 and n. 2). Mg: morning.
Hooker visited CD on 11 July 1874 (Emma Darwin’s diary (DAR 242)).


It would be interesting to prove that some plants feed on decayed animal matter whilst others like Drosera can digest fresh animal matter. Suggests the method for observing this.

Letter details

Letter no.
Charles Robert Darwin
Joseph Dalton Hooker
Sent from
Source of text
DAR 95: 324–5
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9532,” accessed on 5 August 2020,

Also published in The Correspondence of Charles Darwin, vol. 22