To Mary Treat   5 January 1872

Down, | Beckenham, Kent.

Jan 5. 1872

Dear Madam

Your observations & experiments on the sexes of butterflies are by far the best, as far as known to me, which have ever been made.1 They seem to me so important, that I earnestly hope you will repeat them & record the exact numbers of the larvæ which you tempt to continue feeding & deprive of food, & record the sexes of the mature insect.

Assuredly you ought then to publish the result in some well-known scientific journal.2 I am glad to hear that your observations on Drosera will be published.3

I have attended to this subject during several years, & have almost M.S enough to make a volume; but have never yet found time to publish it.

I am very much obliged for yr courteous letter & remain dear Madam | yours faithfully | Charles Darwin

LS

1
In her letter of 20 December 1871 (Correspondence vol. 19), Treat wrote about her observations on Papilio asterias (now P. polyxenes asterius, the black swallowtail butterfly), which suggested that the sex of the adult was determined by amount of time the larva spent feeding.
2
Treat repeated her experiments in 1872 and published the results in American Naturalist (Treat 1873). See Gianquitto 2007, pp. 155–9.
3
See Correspondence vol. 19, letter from Mary Treat, 20 December 1871 and n. 5. Treat’s observations were published in a note submitted by Asa Gray to the American Journal of Science (Treat 1871), and in A. Gray 1872a, p. 44, where Gray wrote of Drosera, ‘in one of our species with longer leaves (D. longifolia) the blade of the leaf itself incurves (as an intelligent lady has observed), so as to fold around its victim!’ Drosera longifolia is now D. anglica (the English sundew).

Please cite as “DCP-LETT-8146,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-8146