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Darwin Correspondence Project

To Edward Frankland   14 May [1874]1

Down, | Beckenham, Kent.

May 14th

My dear Prof. Frankland

I find that I have leaves enough to try Sewage water.2 Will you therefore be so kind as to send me some: of such strength as you wd. feel some surprise at being detected by any one except by a chemist. Perhaps the best plan would be to send only 1 or 2 ounces, & this cd be sent in bottle in little box by post, which wd. save much delay & putrification, as Railway to here is slow.— You could say whether I ought to add twice or thrice as much water to what you send, so as to get the proper dilution.

If what you consider to be weak should act, I could then still further dilute it. I shd use only 1 dr or 12 dr. to each leaf. so very little is wanted. If the fluid contains Phosphate of Ammonia it will certainly act, & almost certainly if it contains the Nitrate of ammonia.—3

In next Nature you will see that I have used your information, & quoted your excellent illustration.4

Yours very sincerely | Ch. Darwin

P.S. If by any chance you have any Oleic Acid in your Laboratory, will you send 3 or 4 gr. if solid or a few drops if liquid. But not worth preparing on purpose   I now suspect that this is cause of Olive oil acting on Drosera; many acids, even such as Benzoic acid, are astonishingly powerful poisons on Drosera & cause inflection; some few acids have no such effect. Acetic acid is powerful.—5


The year is established by the reference to the use of Frankland’s information in Nature (see n. 4, below).
See letter to Edward Frankland, 12 April 1874, and letter from Edward Frankland, 15 April 1874. CD was attempting to determine the sensitivity of the leaves of Drosera.
CD’s experiments with phosphate of ammonia (ammonium phosphate) and nitrate of ammonia (ammonium nitrate) are recorded in Insectivorous plants, pp. 148–66.
Frankland had observed bullfinches removing the nectaries of cowslips (see letters from Edward Frankland, 26 April 1874 and 30 April 1874); CD included these observations in his letter to Nature, 7 and 11 May [1874] (published on 14 May 1874).
The results of CD’s experiments with oleic, benzoic, and acetic acid are reported in Insectivorous plants, pp. 192–3, 194–5, and 191–2, respectively.


Insectivorous plants. By Charles Darwin. London: John Murray. 1875.


Requests sewage water (and oleic acid) for experiments to determine sensitivity of leaves [of Drosera].

Letter details

Letter no.
Charles Robert Darwin
Edward Frankland
Sent from
Source of text
The John Rylands Library, The University of Manchester
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9460A,” accessed on 27 October 2021,

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