The date is established by the relationship between this letter and the letter to W. T. Thiselton-Dyer, 23 November [1880].

In his letter to Thiselton-Dyer of 23 November [1880], CD had expressed an interest in Thiselton-Dyer’s comments about Welwitschia from a now missing letter; CD had thought that the pegs or projections in the seedlings of Abronia (sand verbena) and W. mirabilis might be absorbent organs. Thiselton-Dyer used the term ‘absorbing organ’ in the typical botanical sense, i.e. the sense in which roots absorb water or leaves absorb sunlight (active absorption). CD clearly means it in the sense of staining (passive absorption), since he refers to trying potassium permanganate (KMnO₄) on the peg; see ibid. and n. 4. Frederick Orpen Bower’s paper ‘On the germination and histology of the seedling of Welwitschia mirabilis’ (Bower 1881) was published in the Quarterly Journal of Microscopical Science in January 1881.

CD had asked Thiselton-Dyer to observe whether worms drew the petioles of leaves of Robinia pseudoacacia (black locust or false acacia) into the mouths of their burrows, and, if they did so, by which end, the apex or base; see letter to W. T. Thiselton-Dyer, 23 November [1880].