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Darwin Correspondence Project

From Horatio Piggot   13 September 1877

50 Norfolk Square | Brighton

13 Sept 77

Dear Sir

Allow me to make two or three suggestions that have occured to me in reading your very interesting work on Insectivorous plants at the Library here.

The first is that the experiments in feeding the Drosera with Fly food &c require something more to be done to make them satisfactory: If the plant appropriates or assimilates the fly, it ought to shew it by increase of growth or weight & for this purpose the weight of the plant & the food before & after experiment should be carefully ascertained, & where mineral food has been taken, the residue of the plant should disclose it.1 I do not see except at a footnote p 301 where Mr Knight says a plant &c was much more luxuriant” that any external appearance of the plant would indicate growth from the Fly food:2

I do not know of what compound a fly is composed   I think I have read somewhere that the larva of a fly is a bag of starch. I have often made inquiries among eminent practical Gardeners having the charge of these plants & I have never found one, who agrees with the opinion that the plants derives nourishment from the victim— Saprophytes feed on other plants that have chlorophyll in their leaves— Miseltoe however has Chlorophyll:3 The behaviour of the Droseræ &c is so interesting & their natural history so little really understood that if I might suggest I would erase from the next Edition the passage p. 357 (2nd thousand Copy) beginning “Of the 6 Genera, Drosera has been necessarily the most successful in life &c & a large part of its success may be attributed to its manner of catching Insects”4

It is better not said at present:

I should rather say that it grows in spots the last, from their poverty, that man cares to cultivate & therefore they have survived &c

Again the passage “As it cannot be doubted that this process would be of high service to plants growing on poor soils it would tend to be perfected through natural selection, therefore any ordinary plant having a viscid gland which occasionally caught insects might thus be converted under favorable circumstances into a species capable of true digestion  It ceases therefore to be a mystery how several genera of plants in no way closely related have independently acquired this same power”5

This passage might well find a place in Origin of Species, if you thought it worth while to preserve it but if I might say so, keep the Book on Insectivorous plants closely to its subject, the habits of the plants accurately observed will exhaust a lifetime without theorising.

At present the behaviour of the Droseræ is consistent with the ordinary pursuit of plants, obtaining their food externally from Carbon Dioxide in the air & while enjoying this occupation, keeping themselves, free from Insects by making Examples of such of them as intrude near the Laboratory:

Personally I should like it amazingly to find out that they can feed on Animal food:

The experiment with Carbonates was hardly the thing for vegetables as they never take their food in that form.6

The Secretion of a viscid fluid is as difficult to explain as that of a poison in serpent, & at present no theory of Natural Selection fits their case, & yet they may both be examples of (the residium) of a former state of things when it was necessary to arm plants & animals differently from more usual methods. A few plates & the Experiments thrown into Appendices would make it a very charming readable Book.

I hope you will not think me taking a liberty in writing so fully, I am a Darwinist in part only.

Believe me yr’s faithfully | Horatio Piggot


In Insectivorous plants, CD argued that species of Drosera (sundew) absorbed matter from trapped flies by dissolving them in an acid secretion analogous to the digestive fluids in an animal stomach. Initial experiments designed to prove that the plants derived nutritional benefit from the absorption were inconclusive as the plants died, but Francis Darwin had recently completed similar experiments successfully. He went on to publish the results in a paper on the nutrition of Drosera rotundifolia (F. Darwin 1878a), where he also cited a number of critics who had raised similar concerns to Piggot’s.
In Insectivorous plants, p. 301 n., quoting Kirby and Spence 1818, p. 295, CD recounted that Mr. Knight, a nurseryman in King’s Road, London, had found that a plant of Dionaea muscipula (Venus fly trap) on which he had laid small pieces of raw beef, grew more luxuriantly than others. The original account of Joseph Knight’s observations is in [Duppa] 1809, 1: 43–4.
In Insectivorous plants, p. 453, CD classified four ways in which higher plants obtained nutrition besides the ordinary means of roots, stems, and leaves. He referred to mistletoe (Viscum album) as an example of a class of parasite that fed off living plant hosts, the other classes being those such as Drosera that digested and absorbed animal matter, those like Utricularia (bladderwort) that absorbed decaying animal matter without digesting it, and those like Neottia (bird’s nest orchid) that fed on decaying vegetable matter. Neottia, having no chlorophyll of its own, is an example of a saprophyte; mistletoe, although usually parasitic, has chlorophyll and is capable of growing independently.
Piggot misquotes: the passage reads, ‘Of the six genera, Drosera has been incomparably the most successful in the battle for life; and a large part of its success may be attributed to its manner of catching insects’ (Insectivorous plants, p. 357).
See Insectivorous plants, pp. 362–3.
CD used solutions of carbonate of ammonia (now usually referred to as ammonium carbonate), which is not normally a naturally occurring compound, in many of the experiments described in Insectivorous plants. He discovered that it was particularly effective in stimulating aggregation of protoplasm, which he had identified as the cause of inflection of the tentacles in Drosera.


[Duppa, Richard.] 1809. Elements of the science of botany, as established by Linnæus: with examples to illustrate the classes and orders of his system. 2 vols. London: J. Murray.

Insectivorous plants. By Charles Darwin. London: John Murray. 1875.


Criticises passages of Insectivorous plants. Suggests plants be weighed before and after feeding to prove they have gained nourishment.

Letter details

Letter no.
Horatio Piggot
Charles Robert Darwin
Sent from
Source of text
DAR 174: 44
Physical description
ALS 4pp

Please cite as

Darwin Correspondence Project, “Letter no. 11138,” accessed on 5 December 2022,