See letter from Emma Darwin to W. E. Darwin, [17 May 1864]. By ‘Banting’, William may mean a diet for reducing superfluous fat that had recently been introduced by William Banting (see Banting 1863, and Chambers).

See letter from W. E. Darwin, 18 May [1864] and nn. 7 and 8.

CD’s observations of the dimorphic specimens sent in the tin case are dated 20 May 1864 and are in DAR 110: B51. For William’s drawings of anthers and pollen, see enclosures 1 and 2.

CD noted William’s statement regarding the stigma size of the long-styled flower (see CD’s annotations). When describing William’s collection of Menyanthes trifoliata in Forms of flowers, p. 115, CD wrote that the stigma of the long-styled flower form was larger: ‘as my son observed’. CD also wrote that stigmas from both forms varied ‘much in size’ (ibid.). For CD’s general remarks on stigma size in heterostyled plants, see Forms of flowers, p. 253.

William evidently later added the numbers of short-styled and long-styled flowers from his collection to his notebook entry dated 19 May 1864 (DAR 117: 83). A copy of the notes, in Emma Darwin’s hand, is in DAR 110: B11. CD reported in Forms of flowers, p. 115, the numbers of the two flower forms that William counted.

See letter from H. E. Darwin to W. E. Darwin, [18 May 1864] and n. 3.

See letter from H. E. Darwin to W. E. Darwin, [18 May 1864] and n. 2. In Forms of flowers, pp. 294–5, CD discussed William’s observations of Rhamnus catharticus specimens from the Isle of Wight.

William was an accomplished amateur photographer; he evidently refers to the photograph of CD taken by him that appears as the frontispiece of this volume. He may have taken the photograph during his visit to Down from 21 to 25 April 1864 (see Emma Darwin’s diary (DAR 242)).

The diagram is reproduced at 45 per cent of its original size.

The diagram is reproduced at 45 per cent of its original size.

The calculation, later added by CD, shows that the ratio of the diameter of pollen from short-styled flowers to the diameter of pollen from long-styled flowers is 100 to 84.2 (see Forms of flowers, pp. 115, 249). CD drew the small, rough sketches of a short style with a long stamen and a long style with a short stamen under William’s sketches in enclosure 1. Under each sketch CD also wrote the fractions: these were William’s measurements of pollen diameters in an unknown unit; he presumably gave these to CD at some time after the letter was written. No relevant correspondence or additional pollen sketches have been found, but in Forms of flowers, p. 115, CD wrote after noting William’s collection of Menyanthes: ‘My son made with the camera many drawings of the pollen-grains’.

CD noted the variability of stamen and anther length in Menyanthes trifoliata, and the prevalence of larger anthers in the short-styled flowers, in Forms of flowers, p. 115 (see also CD’s notes in DAR 109: A56, and DAR 110: B10, B51).