From W. T. Thiselton-Dyer   5 June 1874

10 Gloucester Road | Kew

June 5. 1874

Dear Mr Darwin

Let me thank you very much indeed for your most interesting letter.1 I venture to make one suggestion in respect to the Pinguicula which I fancy at the same time can hardly have escaped you

The seeds of the species of Brassica are very rich in Nitrogen. A familiar illustration of this is the fact that Rape cake (Brassica campestris)2 which is the residue after the expression of the oil is employed as a food for cattle and when damaged is even used as a nitrogenous manure. I find on referring to Knop’s tables that Rape seed contains (air dried) nearly 20 per cent of albuminoids3

Believe me | Yours very truly | W. T. Thiselton-Dyer

2
Brassica campestris (rape) is a synonym of Brassica rapa. Although CD had started experiments using cabbage seeds (Brassica oleracea) on 3 June 1874 (DAR 59.1: 39), and had reported that to Thiselton-Dyer (letter to W. T. Thiselton-Dyer, 4 June 1874), there is no record that he used rapeseed in his experiments with Pinguicula (butterwort).
3
According to Wilhelm Knop’s handbook of agricultural chemistry, rapeseed contained 19.4 per cent ‘Eiweisskörper’ (albuminoids) (Knop 1868, 1: 719; see also 1: 695).

Please cite as “DCP-LETT-9484,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-9484