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Darwin Correspondence Project

To Daniel Oliver   21 [September 1860]1

Down Bromley Kent


My dear Sir

I am infinitely obliged for your note.2 The first thought which occurred to me was endosmose (& I tried olive oil & wine).—3 I have tried so many experiments that I cannot think I am in error. I rely much in the case of the saliva experiments on the diminishing effect of weaker & weaker doses. Sulphate & Muriate of Ammonia, Nitrate of Potash & N. of Lime produce none or hardly any effect. With respect to the Vegetable fluids I rely on nitrogenous fluid placed on the same leaves subsequently causing contraction, whereas the vegetable matters produced no effect.—4

Nothing ought to be placed under the leaf as a support, for I have ascertained (in our Drosera) that irritation on the smooth under side of leaf causes contraction.

So small a drop ought to be put on as not to entangle the marginal hairs, as the act of drying of a viscid fluid mechanically draws the hairs together.—

Are you sure that there is no glue with your gum?5 I tried pure white gum & it produced no action at all. Nor did syrup of white sugar or starch.— For Heaven sake try some pure gum.— You have given me a panic. I tried

milk on 9 leaves thin Gelatine on 4 White of egg on 6 Saliva on 8 Urine on 11 Mucus on 4 infusion of meat 1 — 43 leaves.— and all strongly contracted on different plants

I have not tried vegetable fluid so largely only 3 or 4 leaves for each; for absolutely no effect was produced.

Believe me that I am truly grateful for your cautions.—

In Haste | Yours very sincerely | C. Darwin

I start for sea-side tomorrow,6 but letters will be forwarded to me.

P.S | Does not the sourness of your gum prove that it has fermented? And does not fermentation imply that there has been some nitrogenised matter in it? I am nearly sure that yeast is nitrogenised. Most cryptogamic plants certainly contain nitrogen.— For Heaven sake dissolve fresh pure, white gum & try again.7

The inflection of disc of leaf itself, when it occurs is the best of all evidence.—

I fully believe, I have now ascertained that 12880 of grain of N. of Ammonia occasionally suffices with young & very sensitive leaf—, so that scrupulous care is requisite.—8


Dated by the reference to the Darwins’ leaving for the seaside (see n. 6, below).
CD’s notes on experiments to determine the effects of nitrogenous and non-nitrogenous fluids on the leaves of Drosera are in DAR 60.1. The experiments are described in Insectivorous plants, pp. 76–84.
When CD discussed this case in Insectivorous plants, pp. 77–8, he mentioned the problems of impurities in experimental samples of gum. He probably was referring to Oliver when he stated: ‘It is necessary to try pure gum arabic, for a friend tried a solution bought ready prepared, and this caused the tentacles to bend; but he afterwards ascertained that it contained much animal matter, probably glue.’
CD went to Eastbourne on 22 September 1860 (‘Journal’; Appendix II).
Oliver wrote on the letter in pencil: ‘Some bits of clear gum picked’.
The postscript is on a separate slip of paper. The contents indicate that it belongs with this letter.


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


Lists of nitrogenous organic fluids that produce contraction in Drosera, and details of how to reproduce results.

Letter details

Letter no.
Charles Robert Darwin
Daniel Oliver
Sent from
Source of text
DAR 261.10: 11 and part of 17 (EH 88205995, 88206001)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 2923,” accessed on 22 April 2021,

Also published in The Correspondence of Charles Darwin, vol. 8