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Darwin Correspondence Project

To J. H. Gilbert   5 February 1881

Down, | Beckenham, Kent. | (Railway Station | Orpington. S.E.R.)

Feb 5 1881

My dear Sir

I trust to your kindess to forgive me for troubling you with a question. It is, whether vegetable mould, such as occurs close beneath the roots of the grasses on a pasture field, or in a Garden, has an acid reaction. I have tried in a few places & find no signs of acidity by neutral litmus paper, excepting on one damp & not very well drained place on my Lawn, where the mould was distinctly acid.— I ask because I have no experience in such work, & dare not fully trust my own observations.— I have often read of poor soil being “sour”, but imagined that this was only a form of expression for a poor soil.

I have long attended to the action of earth-worms, & I find that the contents of their intestines & their castings (or ejections) are acid, (except when contents were white with chalk) & this leads me to wish to know about mould.1 I have read that the humus acids, (to which class I have some slight reason to believe that the intestinal acids of worms belong) are easily decomposed.—

I hope that it will not cause you much trouble to answer this question, & that you will kindly oblige me.—

My dear Sir | Yours very faithfully | Ch. Darwin

Footnotes

Digestive fluid (pancreatic juice) is alkaline, therefore CD attributed the acidity of fresh wormcasts to the acids produced by the decay of the leaves ingested by earthworms (Earthworms, pp. 50–2).

Bibliography

Earthworms: The formation of vegetable mould through the action of worms: with observations on their habits. By Charles Darwin. London: John Murray. 1881.

Summary

Asks whether vegetable mould has an acid reaction. The contents of intestines of earthworms and castings are acid, which leads him to inquire about mould.

Letter details

Letter no.
DCP-LETT-13038
From
Charles Robert Darwin
To
Joseph Henry Gilbert
Sent from
Down
Source of text
Rothamsted Research (GIL13)
Physical description
ALS 3pp

Please cite as

Darwin Correspondence Project, “Letter no. 13038,” accessed on 28 March 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-13038.xml

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