The year is established by the relationship between this letter and the letter from M. J. Berkeley, 7 March 1856 (see Correspondence vol. 6).

Berkeley had experimented on the immersion in sea-water of seeds of different kinds of plants to determine how long they could remain immersed and still germinate. See Correspondence vol. 6, letter to M. J. Berkeley, 29 February [1856] and n. 3, and letter from M. J. Berkeley, 7 March 1856. The notice CD refers to is ‘On the action of sea-water on the germination of seeds’ (read 6 May 1856; Journal of the Linnean Society (Botany) 1 (1857): 130–40, Collected papers 1: 264–73). CD referred to Berkeley several times in his account of their joint experiments; see also Origin, pp. 358–60. CD’s notes for and manuscript of this paper are in DAR 27.1 E and F. See also Correspondence vol. 5, letter to Gardeners’ Chronicle, 21 November [1855].

In his letter to Berkeley of 29 February [1856] (Correspondence vol. 6), CD mentioned a neighbour’s ‘curious pea with black pods’; Berkeley had suggested the difference might be due to ‘mere variation and not to impregnation’, and asked for a sample (letter from M. J. Berkeley, 7 March 1856).