# To W. T. Thiselton-Dyer   9 June 1874

Down, | Beckenham, Kent.

June 9 1874

My dear Professor Dyer

I was much obliged for your last note.1 I knew that cabbage seeds contained nitrogen, but was not at all aware how much. I have now made out that the action of seeds on Pinguicola, partly depends on their contents, & partly on their coats being more or less permeable to the secretions. The point which now interests me greatly is that seeds excite Pinguicola far more than Drosera; tho’ the latter, by the movement of the tentacles, pours I suppose 20 times more secretion on the seed, & can digest much more animal matter. Hence I suspect that Ping. digests seeds which may be blown on the leaves; improbable as this is.2 And now I am going to ask you several questions of unreasonable length, but not I hope very troublesome.

(1) Do the leaves of all the sp. of Ping. secrete? And are the leaves of all upturned on their edges? This upturning prevents the secretion running off the leaf.

(2) Can you or Hooker give me the address of one or two obliging botanist living near Ping. to whom I cd write, using your name, & ask him to observe the plant, especially about seeds. I have thought of one or two friends, but want several observers.3

(3) Could you send me a very few heath seeds, allied to our British species, to try on Ping?4 Also, any smallish seed destitute of albumen.

(4) Have you any Ping. except P. vulgaris at Kew? & if so, it wd be an immense aid to me if you wd place on a leaf well bedewed with the secretion, a little bit of clean stone, a small crushed fly, & a cabbage seed (enclosed) soaked for $\frac{1}{2}$ an hr in water. And then after 24 hrs, observe the effect of all 3 on the secretion   It would be best to try 2 leaves each with the 3 objects.5

(5) Will you tell me the generic name of the enclosed weed Luzula or Carex(?) grown in a shady wood, as I have used the half-ripe seeds on Ping.6

Pray forgive me for being so troublesome. | yours very sincerely | Ch. Darwin

P.S. I have read that Utricularea catches many insects;7 I suppose you have not plants at Kew, one of which you cd give or lend me.

I see it is allied to Pinguicola.—8

It is a dreadful evil to be so ignorant of botany as I am.

## Footnotes

Letter from W. T. Thiselton-Dyer, 5 June 1874.
For CD’s conclusions, see Insectivorous plants, pp. 385–90. See also letter to W. T. Thiselton-Dyer, 4 June 1874 and n. 4. Pinguicula is butterwort; Drosera is sundew.
CD refers to Joseph Dalton Hooker. Thiselton-Dyer suggested that CD approach John Ralfs (see letter from W. T. Thiselton-Dyer, 25 June 1874; see also letters from John Ralfs, 8 July 1874 and 9 July 1874). Thiselton-Dyer also suggested David Moore (see letter to W. T. Thiselton-Dyer, 28 [June 1874]); in his letter to Moore of 28 June 1874, CD requested help only with Utricularia (bladderwort), but Moore clearly knew of CD’s experiments with Pinguicula (letter from David Moore, 9 July 1874). Others who made observations on CD’s behalf included William Cecil Marshall, Theodosia Louise Marshall, CD’s niece Lucy Caroline Harrison, his son Francis, and Francis’s fiancée Amy Ruck (see letter from T. L. Marshall, 16 July [1874], letter from Francis and Amy Darwin, 8 August [1874], letter from L. C. Harrison, [22 August 1874], and letter from W. C. Marshall, 5 September [1874]). See also letter to ?, 8 June 1874, and letter to W. D. Fox, 18 June 1874.
Among the seeds CD used in experiments on Pinguicula were those of Erica tetralix, the cross-leaved heath (Insectivorous plants, pp. 386–7).
CD concluded, based on similar experiments, that inorganic matter placed on the leaves of carnivorous plants excited far less movement and secretion than organic matter (Insectivorous plants, pp. 22–3, 294–5).
CD’s interest in Utricularia was inspired by a paper on the species by Robert Holland (Holland 1868; see Insectivorous plants, p. 395).
Pinguicula and Utricularia were both in the order Lentibularineae (J. D. Hooker 1870, pp. 296–7), now the family Lentibulariaceae.

## Summary

Did not know cabbage contained so much nitrogen.

Pinguicula more excited by seeds than Drosera. Asks for information about Pinguicula.

## Letter details

Letter no.
DCP-LETT-9486
From
Charles Robert Darwin
To
William Turner Thiselton-Dyer
Sent from
Down
Source of text
Royal Botanic Gardens, Kew (Thiselton-Dyer, W. T., Letters from Charles Darwin 1873–81: 10)
Physical description
4pp