The date range is established by the relationship between this letter, the letter from T. H. Huxley, 12 September 1868, and the letter from C. W. Nunn, 23 September 1868.

The first page of the letter has not been found; however, it evidently concerned Charles William Nunn’s photograph of an ear of wheat with two oat florets growing out of it (see letter from T. H. Huxley, 12 September 1868 and n. 1). For the content of CD’s reply to Nunn, see the letter to J. D. Hooker, 25 September 1868.

In his letter of 12 September 1868, Huxley had mentioned an illness of his son Henry (Harry) Huxley.

See letter from T. H. Huxley, 12 September 1868. CD refers to Joseph Dalton Hooker’s presidential address to the British Association for the Advancement of Science (J. D. Hooker 1868) and John Tyndall’s address as president of the mathematics and physics section (Tyndall 1868). Huxley delivered a lecture ‘On a piece of chalk’ to the working men of Norwich (T. H. Huxley 1868c). Huxley also delivered a lecture, ‘On the distribution of the races of mankind’ (T. H. Huxley 1868d), on 24 August at the International Congress of Prehistoric Archaeology, which was held in Norwich concurrently with the British Association meeting; his lecture was said to be the ‘great event’ of the congress (A. L. Lewis 1869, p. xxviii). For a published report of the congress, annotated by CD and including comments on Huxley’s talk, see DAR 80: B173 v.–174 v. For more on Huxley in Norwich, see the letter from J. D. Hooker, 30 August 1868.