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# To J. D. Hooker   [before 15 July 1874]1

Hooker

Try Fibrin, (as standard test)

— Cartilage (for effect)

— fibro-cartilage, as will not fully digest, but rendered hyaline by Drosera—

Insect in secretion & water for some time

Pour out of virgin pitcher some secretion in watch glass and with it digest a $\frac{1}{20}$th of inch cube of albumen.— If not, then try the same with some secretion from a pitcher which is in the act of Digestion.— Seems to me very important, whether the ferment is secreted only from a stimulus— I understand secretion of virgin pitcher is acid.— We could try Citric acid with pepsin, if we knew proportion of citric acid in the secretion—2

Will you put 6 cabbage-seeds and 3 Peas in secretion & in water for 4 days, & then lay on damp sand under cover in your room & see if they equally germinate. If the Nepenthes seeds do germinate—see whether edge of cotyledons &c are browned & injured.

Please send in tin box with damp moss a piece of the Tropical aerial Epiphytic Utricularia, to look at the bladders3

## Footnotes

The date is established by the relationship between this letter and the letter from J. D. Hooker, 15 July 1874.
CD’s recommendations were for Hooker’s experimental work on the tropical pitcher-plant, Nepenthes (see letter from J. D. Hooker, 1 July 1874 and n. 3). CD wanted to determine whether the fluid in a pitcher of Nepenthes had digestive power if poured out of the pitcher. In Insectivorous plants, p. 97, he noted that Hooker’s experiments showed that the fluid, although acid, had no such power.
This sentence was previously published as the postscript to the letter to J. D. Hooker, 6 November 1873 (Correspondence vol. 21). At the time, this letter and the letter to Hooker of 6 November 1873 were only known from copies, and the copyist had evidently attached this sentence to the wrong letter. The original letters have now been found at Kew. CD had mentioned that he wanted to examine epiphytic species of Utricularia (bladderwort; letter to W. T. Thiselton-Dyer, 28 [June 1874]). All epiphytic species of Utricularia are from tropical America.

## Summary

Suggests experiments to try [with Nepenthes]. Asks JDH to test whether cabbage seeds and peas exposed to the ferment germinate.

## Letter details

Letter no.
DCP-LETT-9523
From
Charles Robert Darwin
To
Joseph Dalton Hooker
Sent from
unstated
Source of text
Royal Botanic Gardens, Kew (JDH/3/6 Insectivorous plants 1873–8: 38–9)
Physical description
3pp

## Please cite as

Darwin Correspondence Project, “Letter no. 9523,” accessed on 21 April 2018, http://www.darwinproject.ac.uk/DCP-LETT-9523

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

letter