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Darwin Correspondence Project

To W. T. Thiselton-Dyer   4 December 1873

Down, | Beckenham, Kent.

Dec 4 1873

My dear Mr Dyer

As Hooker is so busy I shd be very much obliged if you could give me the name of the enclosed poor specn. of Cassia. I want much to know its name, as its power of movement, when it goes to sleep, is very remarkable. Linneus I find, was aware of this.1

It twists each separate leaflet almost completely round, so that the lower surface faces the sky, at the same time depressing them all. The termals2 leaflets are pointed towards the base of the leaf. The whole leaf is also raised up about 12o.

When I saw that it possessed such complex powers of movement, I thought it wd utilize its power to protect the leaflets from rain. Accordingly I syringed the plant for 2 minutes, & it was really beautiful to see how each leaflet on the younger leaves twisted its short sub-petiole, so that the blade was immediately directed at an angle between 45o & 90o to the horizon.3 I cd not resist the pleasure of just telling you why I want to know the name of the Cassia. I shd add that it is a greenhouse plant— I suppose that there will not be any better flowers till next summer or autumn.

Forgive this trouble, & believe | me Yours very sincerely | Ch. Darwin


Joseph Dalton Hooker had recently become president of the Royal Society of London (see letter from T. H. Huxley, 3 December 1873 and n. 2). Cassia is a genus in the family Fabaceae. It was originally described by Linnaeus (Carl von Linné) in Species plantarum (Linnaeus 1753, 1: 376–80). Sleep in Cassia is described in Somnus plantarum (Linnaeus 1755, p. 20).
Probably a mistake for ‘terminal’.
CD added the information on the reaction of Cassia to having its leaves syringed with water to Movement in plants, p. 128.


Linnaeus, Carolus (Carl von Linné). 1753. Species plantarum, exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas. 2 vols. Stockholm: Laurentius Salvius.

Linnaeus, Carolus (Carl von Linné). 1755. Somnus plantarum. Doctoral dissertation of Peter Petersson Bremer under the supervision of Linnaeus. Uppsala: n.p.

Movement in plants: The power of movement in plants. By Charles Darwin. Assisted by Francis Darwin. London: John Murray. 1880.


Wishes to identify a species of Cassia whose movements interest him.

Letter details

Letter no.
Charles Robert Darwin
William Turner Thiselton-Dyer
Sent from
Source of text
Royal Botanic Gardens, Kew (Thiselton-Dyer, W. T., Letters from Charles Darwin 1873–81: 1–2)
Physical description
LS(A) 3pp

Please cite as

Darwin Correspondence Project, “Letter no. 9171,” accessed on 21 February 2024,

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