Following the publication of Orchids in May 1862, CD continued, with assistance from his sons, William, Francis, and George Howard Darwin, to observe, experiment, and keep notes on orchid adaptation and pollination. In a letter to A. G. More, 17 July 1861 (Correspondence vol. 9), CD had expressed the opinion that Orchis latifolia (a synonym of Dactylorhiza incarnata subsp. incarnata, the early marsh-orchid) and the closely allied O. maculata (a synonym of Dactylorhiza maculata, the heath spotted orchid), which some botanists believed to be one species, might be distinguishable by the manner of their insect pollination. He was unable to find conclusive evidence of this before the publication of Orchids (see Orchids, p. 42). However, there is a note in DAR 70: 13–14, dated 20 June 1862, which describes observations by CD’s sons George and William on the pollination of O. maculata by the flies Empis livida and E. pennipes; the note also reads: ‘A D^r. from Southampton sent me 3 flowers of O. latifolia with the smaller black fly [E. pennipes] within the nectary, when he killed it.—’ CD incorporated these observations in the German translation of Orchids (Bronn trans. 1862, p. 22 n.; see the enclosure to the letter to H. G. Bronn, 30 June [1862]). He later published them in ‘Fertilization of orchids’, p. 142, a paper comprising revised and additional notes on orchids, keyed by page number to the first edition of Orchids (see also Collected papers 2: 139).