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Darwin Correspondence Project

From Mary Treat   13 December 1872

Vineland, New Jersey,

Dec. 13, 1872.

Mr. Darwin:

Dear Sir,

Prof. Gray writes me that you have found the nerves in Dionæa.1 Good! And he asks me, in connection with himself, to make observations on Drosera filiformis, which I will gladly do.2

As far as my observations extend, I do not consider this species so interesting as D. longifolia, or D. rotundifolia, although fully as carnivorous as the two latter, yet it captures only small insects which do not require any movement of the leaves to help confine them.

For some reason my plants did not work so well last season as the year before. Whether they were weakened by the unusually dry spring, or whether the locality from which I obtained them was not so good, or whether the fault may not have been somewhat with myself, I cannot say. For two months, commencing in early summer, almost my whole time and thought were concentrated on butterflies in the effort to control sex. The result of my experiments will appear in the American Naturalist.3

My observations and experiments with butterflies, lead me to think that the theory of the Hive bee is not correct. I know that I shall meet with opposition, so the only way is to experiment.4 I have already engaged a Langstroth observing hive for rearing queens,5 and shall carry on these observations, as well as continue my experiments with butterflies the coming season.

Your theory is steadily gaining ground among the masses and thinking people of this country, Prof. Agassiz to the contrary notwithstanding.6 It is boldly advocated from an Orthodox pulpit in this place, and from the Unitarian pulpit we have had a series of discourses teaching the people your theory. Nothing brings out a crowd on Sunday, like the announcement that Darwinism is to be the theme. Surely the world moves!7

Command me in whatever way you may wish observations made, on birds, insects, or plants, and I shall only be too glad to render assistance as far as in my power.

Accept my thanks for your courteous reply to my former letter,8 and believe me | Yours most sincerely, | Mary Treat.

CD annotations

2.2 yet … insects 2.3] scored blue crayon
Top of letter: ‘Dionæa Catches large insects?’ blue crayon


Asa Gray had told CD that he would ask William Marriott Canby to make observations on Drosera filiformis, the thread-leaved sundew (see letter from Asa Gray, 2 December 1872 and n. 5).
Treat’s article ‘Controlling sex in butterflies’ (Treat 1873) was published in March 1873. She concluded from her experiments that the sex of butterflies was not determined in the egg but by how much nourishment the larvae received, females being produced when food was plentiful and males when it was scarce. See also Correspondence vol. 19, letter from Mary Treat, 20 December 1871, and this volume, letter to Mary Treat, 5 January 1872.
The sex of bees was generally thought to be determined in the egg; however, this had recently been challenged by Hartshorne 1872.
Lorenzo Lorraine Langstroth had introduced ‘observing hives’, in which glass walls allowed a continuous view of bees’ behaviour (see Langstroth 1863, pp. 23, 332–3).
For Louis Agassiz’s opposition to evolution, see Lurie 1959.
Treat alludes to the statement ‘Eppur si muove’ (still it moves) said to have been made by Galileo Galilei following his forced recantation before the Inquisition that the earth moved around the sun. It is unlikely that Galileo uttered these words; they were attributed to him only after his death. See Heilbron 2010, p. 327.


Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.

Hartshorne, Henry. 1872. On the relation between organic vigor and sex. American Naturalist 6: 747–51.

Heilbron, J. L. 2010. Galileo. Oxford: Oxford University Press.

Langstroth, Lorenzo Lorraine. 1863. A practical treatise on the hive and honey-bee. 3d edition. New York: C. M. Saxton.

Lurie, Edward. 1959. Louis Agassiz and the idea of evolution. Victorian Studies 3: 87–108.


Drosera filiformis captures only small insects [but see 8989].

Writes of her experiments with butterflies.

CD’s theory steadily gains ground in the U. S., despite Agassiz.

Letter details

Letter no.
Mary Lua Adelia (Mary) Davis/Mary Lua Adelia (Mary) Treat
Charles Robert Darwin
Sent from
Vineland, N.J.
Source of text
DAR 58.1: 23–4
Physical description
ALS 4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 8676,” accessed on 21 June 2024,

Also published in The Correspondence of Charles Darwin, vol. 20