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Darwin Correspondence Project

To Mary Treat   1 June 1876

Down, | Beckenham, Kent. | Railway Station | Orpington. S.E.R. [Hopedene, Surrey.]

June 1st 76

My dear Madam

I have received your kind letter & the article which I have read with the greatest interest. It certainly appears from your excellent observations that the valve was sensitive, & I hope it may be so from homologising with Pinguicula; but I cannot understand why I could never with all my pains excite any movement. It is pretty clear I am quite wrong about the head acting like a wedge.—1 The indraught of the living larvæ is astonishing.— I do not at all understand the German account of the development of the utricles & I suspect that these Germans did not look to young enough utricles.2

I am not well & am staying away from my home for rest, so pray excuse brevity.3 Wishing you success of every kind in your admirable work

I remain | Dear Madam | Yours very faithfully | Ch. Darwin


See letter from Mary Treat, 3 April 1876, and Insectivorous plants, p. 408. Treat’s article, ‘Is the valve of Utricularia sensitive?’ (Treat 1876a), was published in Harper’s New Monthly Magazine in February 1876. There is an annotated copy of it in DAR 226.2: 160–2. Utricularia is the genus of bladderworts; Pinguicula is the genus of butterworts. Treat observed that the movements of insect larvae accidentally touching the valve of the bladder of Utricularia triggered it to open, and that larvae were drawn inside by the partial vacuum thereby created.
See Treat 1876a, pp. 383–4. Treat cited the accounts of Matthias Jacob Schleiden and Ludwig Benjamin as described by Hermann Schacht in a translation sent to her by Asa Gray. See Benjamin 1848, Schleiden 1861, p. 388, and Schacht 1854, p. 28.
CD stayed at Hopedene, Holmbury St Mary, Surrey, from 24 May to 7 June 1875 (CD’s ‘Journal’ (Appendix II)).


Benjamin, Ludwig. 1848. Ueber den Bau und die Physiologie der Utricularien. Botanische Zeitung 6: 17–23.

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

Schacht, Hermann. 1854. Beiträge zur Anatomie und Physiologie der Gewächse. Berlin: G. W. F. Müller.

Schleiden, Matthias Jacob. 1861. Grundzüge der wissenschaftlichen Botanik nebst einer methodologishen Einleitung als Anleitung zum Studium der Pflanze. 4th edition. Leipzig: Wilhelm Engelmann.


Thanks MT for her article ["Is the valve of Utricularia sensitive?", Harper’s New Mon. Mag. 52 (1875): 382–7]. Does not understand why he failed to detect movement [in Utricularia], but it appears from her observations that the valve is sensitive.

Letter details

Letter no.
Charles Robert Darwin
Mary Lua Adelia (Mary) Treat
Sent from
Hopedene Down letterhead
Source of text
Amy Nagashima (private collection)
Physical description
3pp (photocopy)

Please cite as

Darwin Correspondence Project, “Letter no. 10523,” accessed on 14 June 2021,

Also published in The Correspondence of Charles Darwin, vol. 24