The date is conjectured from the reference to CD’s return to Down, and from Horace Darwin’s work on the worm stone (see nn. 2 and 6, below).

CD was in London from 26 to 29 October 1877 (CD’s ‘Journal’ (Appendix II)). The proofs have not been identified.

CD had received a specimen of Ricinus communis (castor-oil plant), along with other plants, from Kew on 3 July 1877 (letter to W. T. Thiselton-Dyer, 9 July [1877] and n. 2). Nutation is the term used to describe the revolving movement made by the tip of various parts of a plant as it grows; in Movement in plants, pp. 1–4, CD expressed his preference for the term circumnutation to describe this movement.

CD was attempting to test the effect of light on plant leaves by blocking it (see letter from Leonard Darwin, 28 November 1877 and n. 2), probably in order to distinguish between circumnutation and heliotropism. For the results of CD’s experiments with blackened oats (Avena sativa), see Movement in plants, pp. 167–8.

Bernard Darwin, Francis Darwin’s son, was just over a year old.

Horace Darwin was building an apparatus to measure the rate at which stones on the surface of the soil are buried by the action of earthworms; it was set up under a large Spanish chestnut tree in the garden at Down House. Horace later reported that in order to construct a fixed point from which the displacement could be measured, a 2.63 metre iron rod was first driven into the ground before being replaced by a copper rod of slightly larger diameter (H. Darwin 1901, p. 253). Horace purchased a copper rod in London around 24 October 1877 (see letter from Emma Darwin to H. E. Litchfield, [c. 25 October 1877] (DAR 219.9: 167). Evidently, the iron rod proved difficult to extract without the aid of the clamp made by the Down blacksmith, William Reeves.

Richard Buckley Litchfield had fallen seriously ill while travelling in Switzerland, owing to inept treatment for acute appendicitis (Litchfield 1910, p. 150).

Possibly the issue of Nature that contained both a sketch of Joseph Dalton Hooker and a paper by him (see letter to J. D. Hooker, [26 October 1877] and n. 4).