The month and year are established by the relationship between this letter and CD’s notes on Robinia mentioning William and dated August 1877 (see n. 2, below).

CD was studying the movements of leaves in plants of the genera Acacia and Robinia (locust trees). During his visit to William in Southampton from 13 June until 4 July, CD had made observations on two species of Acacia and Robinia pseudoacacia (black locust); the notes, dated 15–16 June 1877, are in DAR 209.12: 13. CD continued to study the effects of water on the movement of leaves of Robinia pseudoacacia and mentioned continuing observations by William in notes dated 5–17 August 1877 (DAR 209.12: 163–4). In a note dated 20 August 1877, written at Abinger, Surrey, CD mentioned William’s earlier observation of water beading on leaves of Robinia pseudoacacia after a shower (DAR 209.12: 165). CD visited Abinger from 20 to 25 August 1877 (see ‘Journal’ (Appendix II)).

CD evidently visited Elizabeth Wedgwood’s house in Down before leaving for his stay at Abinger (see n. 2, above). CD had made observations on 4 April 1874 concerning the depression of leaflets from syringing with water; he had made a note to himself to look at Elizabeth’s tree during heavy rain (notes in DAR 209.12: 162).