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Darwin Correspondence Project

To Francis Darwin   2 July [1879]1


July 2d.

My dear F.

We returned home yesterday morning.— Your mother enjoyed her 3 days much & it has rested me.2 Abbadubba was gracious to us & looking the perfection of health vigour beauty & good sense.— Herbert Spencer says in his new book ‘Data of Ethics’, that the ever present idea of causation is the highest point in the evolution of mind, & I am sure that Abbad. has reached the highest point, for his “why”—“what for” &c are incessant.—3 But my object in writing now is to say that it seems to me highly important that cauterising tips of radicles should not prevent apheliotropism or aphelism (N.B. remember to enquire about these substantives), for this shows that it is no absolute consequence of the application of cautic, that the radicles cannot bend (this is an elegant sentence). Do you see what I mean? They do not when cauterised bend geotropically & why shd we say this is owing to injury, when they do bend when cauterised to darkness & likewise owing to “Sachs curvature”.4

your affect. | C. D.

P.S. | I have just started some Sinapis seed, jammed in little holes in cork resting on water to see if they will send their roots into the water, for I shd like to see their apheliotropism, & will perhaps try gold-beaters’ skin & black grease—or very thin tin-foil caps.—5

I have been putting ligatures on fir-branches this morning.6


The year is established by the reference to returning home after three days (see n. 2, below).
The Darwins had stayed at Laura Mary Forster’s house, West Hackhurst, Abinger Hammer, near Dorking, Surrey, from 28 June; they returned to Down on 1 July 1879 (CD’s ‘Journal’ (Appendix II)).
Abbadubba was a pet name for Francis’s son, Bernard Darwin, who was almost 3 years old. Herbert Spencer’s book The data of ethics (H. Spencer 1879) had been published in the second half of June (Publishers’ Circular, 1 July 1879, p. 506). For Spencer’s view on the development of the idea of causation, see H. Spencer 1879, pp. 47–58.
Francis had written that mustard roots to whose tips he had applied caustic (silver nitrate) were still apheliotropic (see letter from Francis Darwin to Emma Darwin, 30 June 1879). For CD’s use of the term ‘Sachs’ curvature’, see the letter to Francis Darwin, 16 June [1879], n. 8. CD had asked Francis to inquire whether the substantive (noun) form of ‘aphelic’ would be ‘aphelism’ (see letter to Francis Darwin, 25 June [1879] and n. 6).
Sinapis is a genus of mustard. CD and Francis were experimenting with S. 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).
CD was planning to remove by ligature all the leading and lateral shoots but one from his silver fir branches (see letter to Francis Darwin, 25 June [1879] and n. 7).


Spencer, Herbert. 1879. The data of ethics. London: Williams and Norgate.


Stresses importance of ensuring that cauterisation of radicles does not, through injury, prevent movement. Plans an experiment to test for "apheliotropism" in certain radicles.

Letter details

Letter no.
Charles Robert Darwin
Francis Darwin
Sent from
Source of text
DAR 211: 60
Physical description
ALS 3pp

Please cite as

Darwin Correspondence Project, “Letter no. 12133,” accessed on 4 March 2024,