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Darwin Correspondence Project

To Francis Darwin   14 July [1878]1

Down, | Beckenham, Kent. | Railway Station | Orpington. S.E.R.

July 14th

My dear F.

Many thanks for all you have done for me.— Keep notes— Why I wish to know about sleeping plants is to give list of Families, as I have observed a good many new cases.—2 My Porliera has had no water for some time, but shows no sign of flagging.3 I have been intending for some time & hope tomorrow to enclose a twig, still on the tree, in bottle with quick-lime, to see effects of locally very dry air.

I have been working very hard all the week, chiefly at Thalia, & at last I have made out whole mechanism: it is a wonderful case— the excitement from a touch spreads from 2 filaments over nectar (which filaments are prolongations of a petal or strictly a staminoid) to the pistil, which instantly (certainly as quickly as Dionæa) curls up into a spire, sweeps the bristle to the opposite side of flower, covering it with pollen, & holding it in a special fold or notch. Just as with Catasetum I cd never help jumping when the pollinia were ejected, so here the sudden snap with which the pistil coils up always makes me jump.4

I have now observed the movements of a score of leaves & of many sleepers, so as to compare the nature of their movements, & it is clear to me that sleep is merely modified circumnutation at a particular time of the day.—

You know some leading shoots are always hooked & I have been observing how they straighten themselves: this again is circumnutation with an excess of movement on the under side of the bowed or convex part. Does not Pfeffer call this hynasty & epinasty or some such names? If you can, do talk about this movement of Pfeffer with Sachs;— it does not seem to me to deserve a special name.—5

Lastly I have a good case with Acacia retinoides of leaves from which bloom had been removed in February being attacked with black smut.6

I hope that you get on with German & profit in many ways from what you see in the Institut.—

How nice it will be to have you home again. Bernard is very sweet & pretty.7

Ever yours affect | C. Darwin

I send Nature8

P.S. Horace suggests that you ask permission to water copiously the plant of Porliera which is out of doors & see if it will then keep awake all day.—9

P.S. | Very many thanks about Sleepers just received— The great thing is fresh Families. I have a Malvaceous plant, but not genus Gossypium so this wd be valuable fact if it sleeps— Do not waste time abt more Leguminosæ unless you see something remarkable & new—10

I do not see that any one (except you occasionally) uses the machine. It is an ugly object in the Smoking Room & I shd. think it a very good thing for me to send it as a present to Sachs   You decide.— I am sure that I shall never endure to have my M.S. copied— Horace does not object to its being given.— All this is written under a mistake— I thought it was Sachs & I see it is Semper— Nevertheless I shd not at all object to give it to Semper— If you decide so, (I do not care an atom about it) it ought to be cleaned & despatched & packed by makers11


The year is established by the reference to Porlieria (see n. 3, below).
Francis had sent some observations on sleeping plants and a list of species that slept (see letters from Francis Darwin, [after 7 July 1878] and [12 July 1878]). CD gave a list of the families of plants that slept (i.e. closed up leaf-blades or leaflets at night) in Movement in plants, pp. 320–1.
A plant of Porlieria hygrometrica was sent to Down on 5 July 1878 (Outwards book, p. 463, Archives, Royal Botanic Gardens, Kew). Francis, after seeing a twig of CD’s plant, had questioned whether the plants in Würzburg and CD’s specimen were the same species, based on the differences in leaf morphology as well as the differences in behaviour (see letter to Francis Darwin, [after 7 July 1878] and n. 3).
For CD’s observations on the floral structure of Thalia dealbata (powery alligator-flag), see the letter to Francis Darwin, 7 [July 1878], the letters to G. H. Darwin, 10 [July 1878] and 11 [July 1878], and the letter to W. T. Thiselton-Dyer, 14 July [1878]. Dionaea muscipula is the Venus fly trap. CD had described the ejection of the pollinia in three species of the orchid genus Catasetum in Orchids, pp. 212–27.
It was not Wilhelm Pfeffer but Hugo de Vries who used the terms hyponasty and epinasty to denote the greater longitudinal growth along the lower or upper side of a plant part that caused upward or downward bending respectively (Vries 1872, p. 252). CD later adopted the terms because they were so often used in Germany (Movement in plants, p. 6). Francis was working in Julius Sachs’s laboratory in Würzburg in the summer of 1878.
CD and Francis were carrying out experiments on the protective function of bloom on plants (CD’s ‘Journal’ (Appendix II)). Acacia retinodes (‘retinoides’ is a misspelling) is swamp wattle.
Bernard Darwin was Francis’s son.
CD evidently sent the weekly issues of the journal Nature to Francis (see letter to Francis Darwin, 7 [July 1878] and n. 5).
Horace Darwin’s suggestion was in response to Francis’s observation that an unwatered Porlieria hygrometrica planted in the ground in Würzburg slept much of the time in contrast to a well-watered potted plant kept indoors (see n. 3, above).
See letter from Francis Darwin, [12 July 1878]. Gossypium is the genus of cotton in the family Malvaceae (mallows). CD was interested in fresh families because he and Francis had already studied several genera within the Leguminosae (a synonym of Fabaceae, the family of peas and beans).
Francis had mentioned that Carl Gottfried Semper wanted to buy a typewriter like the one CD owned (letter from Francis Darwin, [12 July 1878]). Horace Darwin had been so enthusiastic about the typewriter when it was first purchased that he considered getting one for himself (letter from Horace Darwin to G. H. Darwin, 1 May 1876 (DAR 258: 860)).


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

Orchids: On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing. By Charles Darwin. London: John Murray. 1862.

Vries, Hugo de. 1872. Ueber einige Ursachen der Richtung bilateralsymmetrischer Pflanzentheile. Arbeiten des botanischen Instituts in Würzburg 1 (1871–4): 222–77.


Asks for list of families of sleeping plants. Believes sleep is merely modified circumnutation at a particular time of day.

Porlieria has had no water for some time but shows no sign of flagging.

Describes the response of Thalia flowers to touch.

Letter details

Letter no.
Charles Robert Darwin
Francis Darwin
Sent from
Source of text
DAR 211: 35, 36, 39
Physical description
ALS 6pp

Please cite as

Darwin Correspondence Project, “Letter no. 11608,” accessed on 28 May 2023,