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Darwin Correspondence Project

To J. D. Hooker   16 July 1874

Down, | Beckenham, Kent.

July 16 1874

My dear Hooker

Surely the acacia must be the veritable “Bull’s-horns” described by Belt, with the curious little tips which secrete nectar & nourish the protecting ants.1 If you have the plant alive some of you botanists ought to examine the development structure & secretion of the little tips. By the way Fritz Müller tells me (to whom I sent Belt’s book) that he is certain that some Cecropias cannot possibly there exist without the protection of ants.2

I am rather glad you have not been able to send Utricularia, for the common species has driven Frank & me almost mad.3 The structure is most complex. The bladders catch a multitude of Entomostraca4 & larvæ of insects. The mechanism for capture is excellent. But there is much that we cannot understand. From what I have seen today I strongly suspect that it is necrophogous i.e. that it cannot digest but absorbs decaying animal matter.

Foster is certainly in error about the aggregation of the protoplasm: every insect which Drosera catches causes aggregation, & the aggregated matter afterwards redissolves.5 Acids which are poisonous do not cause true aggregation. If I remember right citric acid is innocuous.

Many thanks, I am much better but I had a bad attack on Monday—6

Yours affectly | Ch. Darwin


See letter from J. D. Hooker, 15 July 1874 and n. 2. Hooker had sent CD an Acacia specimen. The reference is to Thomas Belt.
See letter from Fritz Müller, 20 April [1874] and n. 6. Cecropia (the embauba or trumpet tree) is a genus native to the American tropics. Belt’s book was The naturalist in Nicaragua (Belt 1874).
See letter from J. D. Hooker, 15 July 1874 and n. 1. CD and Francis Darwin had recently begun to study Utricularia (bladderwort); the common species is U. vulgaris.
Entomostraca was formerly the name used to refer to all crustaceans other than Malacostraca (Leftwich 1973).
Michael Foster had suggested that the coagulation of protoplasm in Nepenthes could be indicative of disease rather than digestion (see letter from J. D. Hooker, 15 July 1874). CD discussed aggregation in the protoplasm of the glands of Drosera (sundew) in Insectivorous plants, pp. 38–65.
According to Emma Darwin’s diary (DAR 242), CD had a bad attack of diarrhoea and sickness on Monday 13 July 1874.


The Acacia must be Belt’s "Bulls’ horns".

The complexity of Utricularia has driven Frank and CD almost mad. Suspects it is necrophagous, i.e., it cannot digest, but absorbs decaying animal matter.

Foster is certainly in error. Every insect that Drosera catches causes aggregation.

Letter details

Letter no.
Charles Robert Darwin
Joseph Dalton Hooker
Sent from
Source of text
DAR 95: 326–7
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9550,” accessed on 20 June 2019,

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