To Francis Darwin   [9 July 1881]¹

The date is established by the date of CD’s notes on paraheliotropism (see n. 3, below)

The enclosure has not been found, but it was a cutting from Gardeners’ Chronicle, 9 July 1881, p. 42, with an article by Nicholas Edward Brown, titled ‘A locomotive dicotyledon’ (Brown 1881). Brown described the observations of George Watt, professor of botany at the University of Calcutta, on germinating seeds of a plant that he had identified as a species of mulberry mistletoe, Loranthus globosus (a synonym of Macrosolen globosus). Watt observed that when a radicle emerged from the seed, it grew about an inch, then developed a flattened viscid disc, and by repeatedly curving itself and adhering to successive places on the host tree, could move the seed until it reached a favourable site to attach itself permanently, preferentially on a stem. Brown concluded that the movements of the radicle were a form of nutation, and referred to CD’s view that nutation was a universal feature of vegetable growth.

In a note dated 9 July 1881, CD described the alternate rising and falling of all the leaves, except two pinned ones, of Desmodium gyrans (a synonym of Codariocalyx motorius, telegraph or semaphore plant) in full sunshine and cloudy conditions (DAR 209.12: 132). Another note, dated 8–9 July 1881, described observations on Mimosa pudica (shame plant), under a bell glass (DAR 209.2: 147). Paraheliotropism was a term coined by CD to describe the movement of leaves during the day to reduce intense illumination.

For Fritz Müller’s cases of paraheliotropism, see letter from Fritz Müller, 9 January 1881 and n. 8.