skip to content

Darwin Correspondence Project

To Francis Darwin   20 [July 1878]1

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


My dear F.

By same post, I wrote to Semper & offered machine.—2

Is this “rendered account” right; if so return it, & I will pay.—3

I have been speculating roughly & trying to get a heap of cases under one sort of rule, but it is horrid not having you to discuss it with.— Partly from the necessity of the case on evolution principles—I am coming to some such conclusion as follows. Firstly In all growing parts there is an emptying of the cells of water on one side & turgescence on the other; the turgescent cells being in most cases retained in enlarged condition by interception of matter or growth: but there may be the emptying of water without subsequent growth, & that this take place, when movement is required for a long period.

Secondly, that light, gravity, or contact with a solid body produces some effect on side illuminated, acted on by gravity or touched; but that it depends on the good of the plant whether there shall be or shall not be increased turgescence & growth on this side.— The plant merely perceives (so to speak) the light, gravity or touch (on a certain part or place, in its circumnutation, as in case of tendril of Ehinocystis which straightens itself in passing over the terminal shoot) & then turgescence & growth is either increased or eliminated through natural selection on this side according to requirements of the species.—4

But I daresay there are weighty objections to any such generalised view. You might ask Sachs why roots shd be affected by light as they are not naturally exposed to it.—5

Do you know (or could you turn conversation with Sachs) whether most or many true subterranean turn either to or from light, if exposed to it; if they all turn to or from it, as this could be no benefit to root, it wd be a serious objection to above view. One can see why some aerial roots shd be anheliotropic—

Again why does mould turn to light: is light of any use to mould, & does it not properly grow exclusively in dark.6 So many organs of the same kind are geotropic & apo-geotropic, that I cannot believe that gravity in itself tends to increase or decrease growth on one side. It is just possible with radicles as contact makes them bend from an object; so light may act on them in some manner indirectly, though of not slightest use or importance to them.

Yours affect | C. Darwin

Give me any information which you can—


The month and year are established by the relationship between this letter and the letter to C. G. Semper, 19 July 1878.
CD wanted to give his typewriter to Carl Gottfried Semper; Francis had suggested that CD should write to Semper to make the offer (see letter from Francis Darwin, [after 14 July 1878]).
A rendered account is a bill that has been sent but not yet paid. An entry in CD’s Account books–banking account (Down House MS), records a payment of £2 10s. on 22 July 1878 under the heading ‘Morris furniture’, but the entry is clearly in Francis’s hand and out of sequence with other entries, so was probably made retrospectively.
The movement of Echinocystis lobata (wild mock-cucumber) was later described in Movement in plants, pp. 266 and 510.
Francis was working in Julius Sachs’s laboratory in Würzburg.
Although it was clear that light was essential for photosynthesis in green plants, its benefit for moulds was uncertain. Sydney Howard Vines’s research on the movement of moulds (Vines 1878) suggested that heliotropism might have other functions (see letter from W. T. Thiselton-Dyer, 11 May 1878 and n. 3).


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

Vines, Sydney Howard. 1878. The influence of light upon the growth of unicellular organs. Arbeiten des botanischen Instituts in Würzburg 2 (1878–82): 133–47.


Has offered Carl Semper the writing machine.

Speculates on the mechanism of movement in plants and their reception of and response to stimuli.

Letter details

Letter no.
Charles Robert Darwin
Francis Darwin
Sent from
Source of text
DAR 211: 38
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 11620,” accessed on 23 June 2021,