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Darwin Correspondence Project

From Francis Darwin   [before 3 August 1878]1

Botanisches Institut | Würzburg

My dear Father,

Sachs doesn’t know of any negative heliotropic mould; in the Texbook (English) p 677 he says marchantia root hairs & roots of Brassica & Sinapis are negatively heliotropic2   Sachs came in much delighted the day before yesterday having found a number of shoots of Menispermum which had contracted into beautiful corkscrews without having had any sticks given them just as if they were tendrils— he seems to me to jump to conclusions rather; he seems to think now it will be perfectly easy to make out a good case for the similarity of tendrils & twiners. He also found Akebia which had grown down a stick twining round it.3 I have made out clearly that the number of windings increase in the part of the stem that is already wound round the support; that is to say it is not merely the growth of the free end of the shoot, but the growth of the part already touching the support that comes into play. I expect I shall have to come back here to work it out next summer. Sachs promises me a whole greenhouse full of all the plants I want if I can come, but shall certainly go on with it at Down. It is Sachs idea so that if it is to be any good it ought to be done here.

Sachs observed last night a plant of Anagallis pratensis which sends out leafy stems over the ground like Lysimachia, & he said that it was so at night diagram with the bud at the end bent right over.4 I have found a malvaceous plant which sleeps.5


The stalk does not alter but the leaf is 50o below Horizon at night & 10o above in the day; the leaf stalk is a little thickened close to the leaf   Gossypium has a gland on midrib underneath which secretes & is much visited by ants here in the houses.6

I hope you are not bang dead with work dear father | Your affec son | Frank Darwin

See also p. 757 note on Rhizomorphs or root like mycelium of true funguses   There is more about it in 4th Edit   There seems a doubt whether they are apheliotropic after all7

CD annotations

1.1 Sachs … mould;] underl blue crayon
1.3 Sachs came] opening square bracket blue crayon
1.3 Sachs came in … summer. 1.12] crossed red crayon
1.12 Sachs … done here. 1.14] crossed blue crayon
First diagram: ‘Upturning of Leaflet of Leguminosæ see Pfeffer & Wiesner8 pencil
Second diagram: ‘Sleep | get name | Anoda’9 blue crayon
3.2 Gossypium … dear father 4.1] crossed red crayon
5.1 See also … after all 5.3] double scored red crayon
Top of letter: ‘p 17 Akebiapencil


The date is established by the relationship between this letter and the letter to Francis Darwin, 3 August [1878].
Francis was working in the laboratory of Julius Sachs at Würzburg; the laboratory was a centre of research in plant physiology. For his earlier discussion of heliotropism in mould, see the letter from Francis Darwin, 24 and 25 July 1878. Sachs’s Lehrbuch der Botanik (Sachs 1868a) had been translated into English in 1875 (Sachs 1875). Sachs described negative heliotropism in root-hairs (rhizoids) of Marchantia, a genus of liverworts, and in rootlets of Brassica napus (rape) and Sinapis alba (white mustard; Sachs 1875, p. 677).
Menispermum is the genus of moonseed; Akebia is the genus of chocolate vines.
Anagallis pratensis is an unknown combination; Francis probably intended Anagallis arvensis (scarlet pimpernel). Both Anagallis and Lysimachia (loosestrife) are genera in the family Primulaceae (primroses). The diagram is reproduced at 93 per cent of its original size.
Malvaceae is the family of mallows.
Gossypium is the genus of cotton, a member of the Malvaceae family. The glands on the lower midrib of leaves are leaf nectaries; these are found on most species of cotton except G. tomentosum (C. W. Smith and Cothren eds. 1999, p. 336).
The English translation of Sachs’s textbook was made from the third German edition (Sachs 1873), although some of the material from the fourth German edition (Sachs 1874) was added to the notes (Sachs 1875, p. [vii]). For the additional material casting doubt on the negative heliotropism of rhizomorphs, see Sachs 1874, pp. 812–13.
Wilhelm Pfeffer had discussed the upward movement of leaflets of pinnate leaves in Leguminosae (a synonym of Fabaceae, the family of peas and beans) under direct sun, and noted that the movement was referred to by some authors as noonday sleep (Pfeffer 1875, pp. 62–3 and n. 2). Julius Wiesner had referred to Pfeffer’s observations and reported his own observations of movement in leaflets of Robinia (Wiesner 1876, pp. 45–6). An abstract of Wiesner 1876 appeared in Der Naturforscher, 26 August 1876, pp. 327–9; CD’s heavily annotated copy of this abstract is in the Darwin Pamphlet Collection–CUL.
Anoda is a genus of plants in the family Malvaceae; CD evidently added the name when Francis supplied it, but no letter from Francis referring to it has been found. Notes on the movement of the petiole in leaves of Anoda wrightii (a synonym of A. lanceolata, lanceleaf anoda), written by Francis, dated 30 July to 2 August 1878, are in DAR 209.14: 6–7.


Pfeffer, Wilhelm. 1875. Die periodische Bewegungen der Blattorgane. Leipzig: Verlag von Wilhelm Engelmann.

Wiesner, Julius. 1876. Die natürliche Einrichtungen zum Schutze des Chlorophylls der lebenden Pflanze. In Festshrift zur Feier des funfundzwanzigjährigen Bestehens der k. k. zoologisch-botanischen Gesellschaft in Wien. Vienna: W. Braumüller. Leipzig: F. A. Brockhaus.


Sachs jumps to the conclusion twiners and tendrils are similar from the Menispermum that twined without a stick. Akebia grows down a stick; not only the free end is involved.

Sleeping plants.

Letter details

Letter no.
Francis Darwin
Charles Robert Darwin
Sent from
Source of text
DAR 209.8: 152
Physical description
2pp †

Please cite as

Darwin Correspondence Project, “Letter no. 11638,” accessed on 6 May 2021,