# 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 $\frac{1}{10}$ 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

## Footnotes

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)).

## Summary

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.
DCP-LETT-9532
From
Charles Robert Darwin
To
Joseph Dalton Hooker
Sent from
Down
Source of text
DAR 95: 324–5
Physical description
4pp

## Please cite as

Darwin Correspondence Project, “Letter no. 9532,” accessed on 24 May 2019, http://www.darwinproject.ac.uk/DCP-LETT-9532

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

letter