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Darwin Correspondence Project

From J. T. Moggridge   4 November 1873

Maison Gastaldy | Mentone | (Alpes Maritimes | France)

4 Nov. | 1873

My dear Sir

We returned to Mentone on the 21st. of last month—1

I have been able to recommence, & am deeply interested in, my experiments with formic acid vapour & seeds, though I am still somewhat hindered by the remains of an attack of bronchitis caught on the journey—.

Though I do not absolutely despair of eventual success in the primary aim of my experiments I must own that I am some way yet from being able to treat the seeds with the same results as those obtained by the ants, though I have succeeded in a few exceptional cases in rendering a few seeds dormant while under the influence of the acid vapour without impairing their power for subsequent germination.2

I am now repeating & varying my experiments with 1 minim formic acid to 2 m. distilled water, this being the mixture which gives the more promising results.—

A great deal appears to depend upon the vigour of the individual seeds, & I am greatly struck by the evidence which these experiments afford of the variability of the constitution of seeds.

In my 26 latest experiments 6 peas, 6 cress and 6 millet only have been employed; & I find that this diminution in the number of species used in each experiment greatly facilitates accurate observation of the condition of the seeds, & enables me to select plump & health-looking seeds in every case.—

I find that cress seeds suffer most, millet next & peas least. Garden peas usually succeed in pushing out the radicle when less than 1 min. f. a. to 4 dist. w. is used, but, even when such dilute mixtures as 12 min. f. a. to 16 or even 19 min. distilled water are employed, the growth is always markedly checked, however vigorous the individual may be, & most frequently the radicle is paralysed or killed.—

The little drawings enclosed, which I have copied for you from my original sketches, illustrate the kind of effect produced—3

The shortness of the radicle or fibril, & the absence of papillae on its surface, are the most marked features which distinguish seeds which have attempted to germinate under the influence of acid vapour from seeds in the early stages of normal germination. In dicotyledons the coats of the seed appear frequently to cling round the tip of the radicle & to resist its attempts to free itself.

I am endeavouring now to find the point at which the addition of water will so weaken the effects of 12 min. of f. a. that germination will proceed normally as if no acid were there.—

I think it will be possible to prepare an instructive series of drawings shewing the different degrees in which half-a-dozen seeds of the same kind are affected by the vapour of 12 min. f. a. greatly diluted—. I have made two experiments with living ants, imprisoning them in covered tumblers in place of the acid mixture.

In the first 10 individuals of Atta structor, &, by mistake, one Formica fusca, were placed, & the seeds germinated normally & were not disturbed by the ants.4

The same was the case in the second experiment, where 20 individuals of Atta barbara5 were imprisoned—

Now Atta barbara & A. structor, our principal harvesting & seed-storing ants, do not give off any smell that I can detect even when crushed, & I am curious to repeat the experiment with an equal number of ants of some other species which have a strong formic-acid smell.

When very large numbers of seeds are exposed to the acid vapour I found, in the one experiment made, that they germinated without any apparent hindrance, though the same amount of acid had previously paralysed or killed half-a-dozen of each of the same kinds of seeds. Thus I tried 100 cress, 100 millet & 20 peas in a covered tumbler with 12 min. f. a. in 1 min. water renewed twice a day, & the germination was unimpeded.

However, I do not find that 12 seeds of each kind suffer perceptibly less than 6 do.—

We must remember that, in the ants’ granaries, the seeds are not only very numerous but also of very many different kinds.— Perhaps this may suggest some fresh opening for experiment—

I must ask you to forgive an untidy & rather incoherent letter—. | Believe me always | Yrs. most sincerely | J. Traherne Moggridge.

May I ask you to have the enclosed posted.6


Mentone (now Menton) is a town on the French Riviera near the border with Italy, where Moggridge spent most winters owing to his chronic ill health (R. Desmond 1994).
Moggridge had been performing experiments to ascertain whether formic acid retarded the germination of seeds (see letters from J. T. Moggridge, 30 July 1873 and 22 August 1873). He reported the results of these experiments in Moggridge 1874, pp. 170–4.
The drawings have not been found.
Atta structor is now Messor structor; Formica fusca is the common European black ant.
Atta barbara is now Messor barbarus, the Mediterranean harvester ant.
The enclosure has not been identified.


Desmond, Ray. 1994. Dictionary of British and Irish botanists and horticulturists including plant collectors, flower painters and garden designers. New edition, revised with the assistance of Christine Ellwood. London: Taylor & Francis and the Natural History Museum. Bristol, Pa.: Taylor & Francis.

Moggridge, John Traherne. 1874. Supplement to Harvesting ants and trap-door spiders: with specific descriptions of the spiders by the Rev. O. Pickard-Cambridge. London: L. Reeve & Co.


Formic acid kills seeds but only rarely makes them dormant – as he presumes ants do. He finds great variation in the vigour of individual seeds. Harvester ants, used in place of formic acid, do not affect germination.

Letter details

Letter no.
John Traherne Moggridge
Charles Robert Darwin
Sent from
Source of text
DAR 171: 223
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 9133,” accessed on 23 October 2020,

Also published in The Correspondence of Charles Darwin, vol. 21