To Daniel Oliver   21 [September 1860]1

Down Bromley Kent

21st

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

1
Dated by the reference to the Darwins’ leaving for the seaside (see n. 6, below).
4
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.
5
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.’
6
CD went to Eastbourne on 22 September 1860 (‘Journal’; Appendix II).
7
Oliver wrote on the letter in pencil: ‘Some bits of clear gum picked’.
8
The postscript is on a separate slip of paper. The contents indicate that it belongs with this letter.

Manuscript Alterations and Comments

1.2 (& …wine)] interl
1.3 case of the] interl
1.4 weaker & weaker] above del ‘less & less’; ‘&’ not del in error
1.4 Sulphate] after del ‘With’
1.5 none or] interl
4.2 of white sugar] interl
4.2 Nor … starch.—-] added
5.1 I have … was produced. 5.2] added

Please cite as “DCP-LETT-2923,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-2923