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 of grain of N. of Ammonia occasionally suffices with young & very sensitive leaf—, so that scrupulous care is requisite.—8
Lists of nitrogenous organic fluids that produce contraction in Drosera, and details of how to reproduce results.