To Francis Darwin   25 June [1879]1

June 25th

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

My dearest F.

Your mother forgot to give me your letter of yesterday until the evening after I had written.2 Remember to keep beans not above 60o F. if possible.— Would it not be well to show Sachs effect of touching apex once lightly one side.3

If I were you I wd not try many experiments at Wurzburg, which you could try here.

I am very glad to hear about Mustard seed; for I am very curious to learn how far apex is the governing point for movements relatively to light.— But I think you did try this here.4 With aerial roots it wd be much better to cover tips (& this is easily done) with Gold-Beaters skin (I enclose some in case you like to try it) & coat some with Black paint thickly & leave others with the Gold-beaters transparent.5

What-ever Sachs may say, it seems to me important to prove that an aphelic organ grows quicker in dark— it is good concurrent evidence that light is only the regulator & not cause of movement.

I would use proshelic & aphelic.—if substantives can be made— Would proshelism do instead of heliotropism, & so with aphelism.— If not I think I will stick to Heliotropism & apheliotropism—to heliotropic & apheliotropic.— Ask Goebel about this—6

My fir-trees will on our return be ready for ligature of leading & all the lateral shoots but one.—7

I shall be curious hereafter to have explained your spiral theory about revolving nutation or circumnutation—8 It seems probable;—but remember an ellipse—often very narrow—is usual figure described.

I am getting to hate the work, & wish all radicles were deep in the earth.

Ever yours affect | C. Darwin

Do not forget Porliera9

1
The year is established by the relationship between this letter and the letter to Francis Darwin, 24 June [1879].
2
See letter to Francis Darwin, 24 June [1879]. The letter from Francis was probably that of [after 16 June 1879].
3
CD found that temperatures above 70°F (21°C) destroyed the sensitivity to irritation of bean (Vicia faba) radicles; in experiments where a piece of card was attached to one side of the root tip, CD found that the root bent away from the irritation of the card. Julius Sachs had performed similar experiments, but his beans were kept at high temperatures and he did not detect any sensitivity in the apex (see Movement in plants, p. 142).
4
See letter from Francis Darwin, [after 16 June 1879] and n. 4. Francis’s notes, dated 29 and 30 April, and 7, 12, and 13 September, on the application of caustic to mustard radicles, are in DAR 209.7: 71.
5
On CD’s use of gold-beater’s skin, see letter to ?, 23 January [1879?], nn. 1 and 2.
6
Karl Goebel, a botanist in Sachs’s laboratory, had suggested the terms proshelic and aphelic to refer to movement towards or away from light (see letter from Francis Darwin, [after 16 June 1879].
7
The Darwins were away from home between 26 June and 1 July 1879, first in London where CD was to be awarded the Baly medal and then at the home of a friend, Laura Mary Forster (CD’s ‘Journal’ (Appendix II); see letter to Francis Darwin, 24 June [1879] and n. 6). On CD’s interest in the apogeotropism of abnormal shoots found in silver fir trees affected by a fungus, see the letter to Francis Darwin, 2 June [1879] and n. 6.
8
See letter from Francis Darwin, [after 16 June 1879] and n. 5. Revolving nutation was the term used by Sachs: CD referred to this movement as circumnutation (see Movement in plants, p. 1).
9
On Francis’s recent work on Porliera (a synonym of Porlieria), see letter to Francis Darwin, 16 June [1879] and n. 3.

Manuscript Alterations and Comments

1.3 apex] above del ‘just’
1.3 side.] before del ‘of apex—’
3.2 the] interl
3.2 movements relatively to] interl
3.3 (& … done) 3.4] interl
3.4 skin] interl
10.1 … Porliera] added pencil

Please cite as “DCP-LETT-12122,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-12122