Lists of nitrogenous organic fluids that produce contraction in Drosera, and details of how to reproduce results.
Down Bromley Kent
My dear Sir
I am infinitely obliged for your note. The first thought which occurred to me was endosmose (& I tried olive oil & wine).— 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.—
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? 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, 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.
The inflection of disc of leaf itself, when it occurs is the best of all evidence.—
I fully believe, I have now ascertained that
- f1 2923.f1Dated by the reference to the Darwins' leaving for the seaside (see n. 6, below).
- f2 2923.f2Letter from Daniel Oliver, 19 September 1860.
- f3 2923.f3See letter from Daniel Oliver, 19 September 1860 and n. 3.
- f4 2923.f4CD'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.
- f5 2923.f5When 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.'
- f6 2923.f6CD went to Eastbourne on 22 September 1860 (`Journal'; Appendix II).
- f7 2923.f7Oliver wrote on the letter in pencil: `Some bits of clear gum picked'.
- f8 2923.f8The postscript is on a separate slip of paper. The contents indicate that it belongs with this letter.