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Darwin Correspondence Project

To W. T. Thiselton-Dyer   1 July 1874

Down, | Beckenham, Kent.

July 1 1874

My dear Mr Dyer

Very many thanks for your interesting letter.

You have not the least cause to apologize, for I enjoyed sending you my notes.1 I think I have solved both the puzzles with which I before concluded.

A solution of C. of ammonia & an infusion of raw meat, both cause inflection: I failed before because I tried a sol. of 2. gr to 1 oz, & just as with Drosera, a strong sol. paralyses the plant (tho’ causing aggregation) so it does with Pinguicola.2 If a sol. of meat be dropped along the midrib, the 2 sides approach each other; but if the drop spreads a little on one side, it sends a motor influence to the extreme margin of that side, which becomes involuted. In all cases the bending inwards ceases after 24 hrs & the edges of the leaf bend back again, & I was wrong in supposing that the object was to pour secretion over the fly, tho’ a very little is thus poured. The real object seems to be to push the fly or bit of meat further on the leaf, by which means it is brought into contact with many glands.3 I have ascertained this by experiment. In this case the object food is moved, whereas with Drosera, the glands move to the object. I ought before to have stated that the footstalks of the glands have not the least power of inflection—

yours very sincerely | Ch. Darwin


See letter from W. T. Thiselton-Dyer, 26 June 1874; the letter is incomplete and the section where Thiselton-Dyer apologised is missing. CD had sent Thiselton-Dyer his notes on Pinguicula (butterwort), and Thiselton-Dyer communicated a summary of these to the Royal Horticultural Society; see letter to W. T. Thiselton-Dyer, 28 [June 1874] and n. 4.
CD recorded experiments with different strengths of solution of carbonate of ammonia on 22 June 1874 (DAR 59.1: 54). CD noted the paralysing effect of a strong solution on Pinguicula in Insectivorous plants, p. 376.
The published summary of CD’s communication to the Royal Horticultural Society had concluded with an expression of CD’s uncertainty about the meaning of the inflection of the margin of a leaf of Pinguicula


Describes leaf movements of Pinguicula and Drosera in capturing prey. Notes effects of ammonium carbonate on leaves.

Letter details

Letter no.
Charles Robert Darwin
William Turner Thiselton-Dyer
Sent from
Source of text
Royal Botanic Gardens, Kew (Thiselton-Dyer, W. T., Carnivorous Plants)
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9527,” accessed on 21 May 2019,

Also published in The Correspondence of Charles Darwin, vol. 22