The date is conjectured from the relationship between this letter and the letter from A. R. Wallace, 26 September 1863; the first Tuesday after that date was 29 September.

See letter from A. R. Wallace, 26 September 1863.

CD stayed at Malvern Wells, Worcestershire, from 3 September to 12 or 13 October 1863, in order to undergo treatment at James Smith Ayerst’s hydropathic establishment (see Emma Darwin’s diary (DAR 242) and letter to J. B. Innes, 1 September [1863]).

See letter from A. R. Wallace, 26 September 1863 and n. 2. CD never published his research on the Melastomataceae (see Cross and self fertilisation, p. 298 n., and ML 2: 292–302); his working notes on the subject are in DAR 205.8.

See, for example, letter to Hugh Falconer, 5 [and 6] January [1863] and nn. 22–3, letter from John Scott, 6 January 1863, letter to H. W. Bates, 12 January [1863], letter to Asa Gray, 19 January [1863], and letter to Hermann Crüger, 25 January [1863].

See letter from A. R. Wallace, 26 September 1863. CD discussed the acclimatisation of domesticated varieties in Variation 2: 305–15; however, he did not cite the case supplied by Wallace in Variation, or in any of his subsequent publications.

CD refers to a report in the Reader 2 (1863): 352–3, describing Wallace’s paper, ‘On the geographical distribution of animal life’ (Wallace 1863c), which was read on 31 August 1863 at the annual meeting of the British Association for the Advancement of Science in Newcastle-upon-Tyne. The report made no reference to the discussion of Wallace’s paper; however, it was followed by a report of Henry Baker Tristram’s paper, ‘On the variation of species as pointing to Western Asia as the centre of the palæarctic area of creation’, in which Tristram referred to Wallace’s ‘magnificent epitome of all that science had yet attained in respect to the variations and limits of the different groups’. There are annotated copies of both reports in DAR 205.10: 2.