To Francis Darwin   25 July [1878]1

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

July 25

My dear F.

Semper seems much pleased about the machine & has written me an uncommonly nice letter.2 The machine has just started for London to be cleaned, packed, & despatched to Würzburg.—

Thanks for your last long letter, all of which I have enjoyed much, but you must not waste time by writing again—3 I am glad to hear about the sleep of the Leguminosæ, but you seem to find little else in any other Families.— My Porliera has never been watered & the earth seems as dry as dust, but the leaves are still awake in the day.4

It rejoices me to hear that you are working at my old friends the twiners: how I did enjoy the work, but how much better I shd. have done it now; for I rarely then made tracings.—5 It is quite new to me about the supplementary little circles of Cobæa, & it throws light on what I have often noticed of late in the circumnutation of non-climbing plants.6

I think that De Vries has proved that there is increased growth along one side of tendril where it curls up spirally.—7

The Helvingia is a most curious case, & I am particularly glad that you will observe it, & you are a good fellow, for I know that you hate bloom.8

I am sorry Sachs is so severe on men, as that is a character which I dislike: by Jove the Moscow man (Mery……?) returned the compliment in his last paper.9

Since I wrote last I found old note by Dyer about mould turning to light, & I must modify the rough notion which I wrote to you; but I think that I can “wriggle” out.—10 If you possibly can find out from Sachs whether any moulds are apheliotropic, & whether any roots are apheliotropic or are they all heliotropic.

Subterranean roots are the most perplexing.—

Hooker is going to hunt up & send me heliotropic aërial roots.— Hooker was very nice when here, though hot about Turkey.11

I am working hard at peduncles of Trifolium subterraneum, which buries its flower-head, after flowers are fertilised; there seems much odd about whole case.12

Yours affecty. C. Darwin

(I do not understand movements of Adenanthera)13

Say to Sachs how proud I shd be to see him at Down, if he can spare time & if we are at home.

CD annotations

7.3 If … heliotropic. 7.4] scored red crayon
1
The year is established by the relationship between this letter and the letter from C. G. Semper, 22 July 1878.
2
See letter from C. G. Semper, 22 July 1878. CD was giving his typewriter to Carl Gottfried Semper.
3
Francis planned to return home on 8 August 1878 (see letter from Francis Darwin, [21 July 1878]).
4
Francis had reported that the leaves of a Porlieria planted in the ground in the Würzburg garden were tightly closed (see letter from Francis Darwin, [21 July 1878] and n. 10). CD’s observations were made on a plant he had borrowed from Kew (see letter to Francis Darwin, 6 [July 1878]). Leguminosae (a synonym of Fabaceae) is the family of peas and beans; CD wanted to find sleeping plants from other families (see letter to Francis Darwin, 14 July [1878] and n. 2).
5
CD carried out numerous experiments on climbing plants in 1863 and 1864. His paper, ‘Climbing plants’, was read before the Linnean Society on 2 February 1865 and appeared in book form (Climbing plants) in the same year; a second edition was published in 1875 (Climbing plants 2d ed). CD had been tracing the movement of plants on glass to show that sleep movement was modified circumnutation (see letter to Francis Darwin, 14 July [1878]).
6
Francis had made tracings showing the circumnutation of a tendril of an unnamed species of Cobaea; the tendril made both a broad sweeping movement and several small spiral movements within a given time period (see letter from Francis Darwin, [21 July 1878] and n. 4). CD concluded that the great sweeps made by twining stems or tendrils were a modified form of ordinary circumnutation but with greatly increased amplitude (Movement in plants, p. 3).
7
Francis mentioned he wanted to read Hugo de Vries’s work on the mechanics of bending in climbing plants (see letter from Francis Darwin, [21 July 1878] and n. 6). De Vries had studied the relation between between growth and bending (Vries 1873a and 1873b); he later showed that growth was a secondary effect, and that the curvature was produced by increased turgescence of the cells on the convex side (Movement in plants, p. 2).
8
Julius Sachs had shown Francis fruits of Helvingia rusciflora (a synonym of Helwingia japonica). Francis noted that flowers were full of juice and covered with bloom and planned to investigate whether the bloom served to protect the petals from moisture (see letter from Francis Darwin, [21 July 1878]).
9
Kliment Arkady Timiryazev of Moscow, in his paper ‘Sur la décomposition de l’acide carbonique dans le spectre solaire, par les parties vertes des végétaux’ (On the decomposition of carbonic acid in the solar spectrum, by the green parts of plants; Timiriazeff 1877, pp. 382, 395), suggested that Sachs’s belief that the light rays that produced the maximum decomposition could be determined was based on Sachs’s ignorance of the conditions related to the problem; he also strongly criticised Sachs’s view that the fact that both animal eyes and plants exhibited a proportional response to light intensity was purely accidental. He concluded that Sach’s opinion was repugnant to the scientific spirit, to logic, and to the facts. Three offprints of Timiriazeff 1877, one inscribed by the author, are in the Darwin Pamphlet Collection–CUL. For more on CD’s interest in proportional responses to light intensity, see the letter from G. H. Darwin, 10 October 1878.
10
See the letter to Francis Darwin, 20 [July 1878], in which CD wondered why moulds would turn towards light if it was of no use to them. William Turner Thiselton-Dyer had expressed his views on heliotropism in moulds in his letter of 11 May 1878.
11
Joseph Dalton Hooker had visited Down from 20 to 22 July 1878 (Emma Darwin’s diary (DAR 242)). On 13 July 1878, the major European powers had replaced the Treaty of San Stefano, which had been signed by Russia and Turkey at the end of the Russo-Turkish War in March 1878, with the Treaty of Berlin. The Treaty of Berlin revised the peace settlement to serve the interests of Great Britain and Austria-Hungary by re-establishing Turkish rule and maintaining the Ottoman Empire as a European power, despite widespread condemnation of the Turks for atrocities in Bulgaria in 1876. (Medlicott 1963, pp. 6–7.)
12
CD later discussed Trifolium subterraneum (subterranean clover) in Movement in plants, pp. 513–17, explaining that it was the motion of continued circumnutation after the flower heads had reached the ground that enabled them to be buried.
13
In his letter of [21 July 1878], Francis Darwin had referred to the slight sideways twisting of leaves of Adenanthera pavonina (red beadtree), and added that this seemed to be the ‘only slightly new movement’.

Manuscript Alterations and Comments

2.1 last] interl
2.1 have] interl
2.2 sleep of the] interl
2.3 in … Families.] interl
2.4 the earth] interl
3.2 now;] semi-colon altered from point
3.2 for … tracings. 3.3] interl
3.4 of late] interl
5.2 &] over ‘for’
5.2 you] above del ‘you’
8.1 Subterranean … perplexing.—] added
9.2 hot] above del ‘hot’
13.1 Say … home. 13.2] added pencil

Please cite as “DCP-LETT-11631,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-11631