To Francis Darwin   28 June [1879]1

Laura’s House

June 28th

My dear Frank

Here we are & remain till Tuesday morning, & George comes down to night.—2 I had a very busy day yesterday; first good talk with B. Sanderson who was interested about the circumnutation & starting movement under microscope of Dionæa & means to go into it in relation to electric currents:3 then a very pleasant luncheon at Pagets, & in evening a talk with Lauder Brunton, who is reading Zoonomia & is enthusiastic about Dr. D.—4

Your letter arrived just as we were starting for Q. Anne St: I am very sorry that Sachs is so sceptical, for I wd. rather convert him than any other half-dozen-Botanists put together; but I expected it.5 No doubt something may be said against caustic. I do not understand why when radicles are pointed perpendicularly down & then tips are cauterised they grow out wildly on all sides, & this does not happen when they are extended horizontally; I suspect that ‘Sachs’ curvature’ comes into action only with perpendicular roots, & will set to work & observe this point.6 It seems to me a sufficient explanation of geotropism acting after 24 h, though not at first, that some of the cells of the apex regenerate themselves.— I shd. not at all believe in the sense of geotropism residing in apex, if I did not feel sure about the sense of contact residing there. It was observing radicles of Beans sliding down unsmoked glass, & the manner in which they turned at right angles (quite unlike any mechanical bending) when their tips encountered a strip of wood or glass cemented across the plate, that made me first suspect sensitiveness & try the little square of card first with gum & then shell lac. It is the side of conical tip which is alone sensitive.— Whenever card got parallel to radicle it did not act.—

diagram

In crawling down glass-plate side of conical apex does not touch glass-surface, except just at first, when it first comes into contact & then it rises a trifle & adjusts itself. I wish it were possible to try radicles of mustard with black cap instead of caustic—7 Though it is quite possible their sensitiveness may not be confined to tip— nor shd I expect it, to be so confined except in cases, as of aerial roots, when it is probably of service to plant.— Great man as Sachs is, I am not even staggered by him.

I am tired— goodbye my dear old fellow | C. Darwin

1
The year is established by the address; the Darwins stayed at the home of Laura Mary Forster, West Hackhurst, Abinger Hammer, near Dorking, Surrey, from 28 June until 1 July 1879 (CD’s ‘Journal’ (Appendix II)).
2
The Darwins had just arrived at West Hackhurst (see n. 1, above). George Howard Darwin had been in London doing research on the Darwin family for CD (see letter from G. H. Darwin, 24 June 1879 and n. 1).
3
John Scott Burdon Sanderson had previously assisted CD with his research for Insectivorous plants and had published on electrical phenomena associated with leaf contraction in Dionaea muscipula (Venus fly trap; see Burdon Sanderson 1873a, 1873b, 1874a, and 1874b).
4
James Paget and Thomas Lauder Brunton were consulted by CD for information about Erasmus Darwin’s medical practice; CD was writing an introductory biographical sketch of his grandfather for Erasmus Darwin.
5
See letter from Francis Darwin, [before 26 June 1879]. CD went to London on 26 June 1879; the Darwins stayed at the home of CD’s brother, Erasmus Alvey Darwin (CD’s ‘Journal’ (Appendix II)). In his letter from Francis Darwin, [before 26 June 1879], Francis told CD that Julius Sachs was unconvinced by CD’s experimental results suggesting that the apex of the radicle was geotropic.
6
Sachs had suggested that the use of caustic (silver nitrate) interfered with CD’s results by causing injury to the root (letter from Francis Darwin, [before 26 June 1879]). On ‘Sachs’ curvature’, see the letter to Francis Darwin, 16 June [1879], n. 8.
7
CD and Francis were experimenting with Sinapis alba (white mustard); Francis had observed strong apheliotropism in the roots of this species (see letter to Francis Darwin, 6 and 7 June [1879] and n. 5, and letter from Francis Darwin, [after 16 June 1879] and n. 4).

Manuscript Alterations and Comments

1.2 day] after del ‘interes’
1.3 under microscope] interl
1.5 & is] ‘is’ interl
2.1 for … St] interl
2.5 are] above del ‘was’
2.5 does] above del ‘did’
2.6 curvature] after del illeg
2.7 & will … point.] interl
2.9 some … cells of] interl
2.9 the sense of 2.10] interl
2.12 (quite … bending) 2.13] interl
2.14 little square of] interl
2.15 alone] interl
3.1 crawling] above del ‘crawling’
3.2 except … itself. 3.3] added
3.5 nor] above del ‘Nor’
3.5 expect it] ‘it’ above ‘expect’
3.5 so confined] interl
3.6 Great] above del ‘Great’

Please cite as “DCP-LETT-12128,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-12128