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Letter from Charles Robert Darwin to Francis Darwin 6 [July 1878]1
Down, | Beckenham, Kent. | Railway Station | Orpington. S.E.R.
6th.
My dear F.
They have sent a magnificent bush of Porliera covered with leaves—2 Compare twig with your plant— no vestige of bloom— To day cloudy every leaf wide awake! Will have it in study to night & see how it sleeps, if it does sleep.—
I am dead with work & talk with McLennan, but have splendid success with radicles of Maize.—3
Case just reverse of bean— must be kept hot & then every single radicle with squares on tips on cork hooked & wound like French Horns—whereas 20 radicles with no squares as straight as arrows— Case splendidly conclusive. But the bother is great of finding out temperature at which radicles become sensitive.4 Therefore I shall not do many more, as we have a Dicot. & Monocot.
Yours affect | C. Darwin
3.1 with … tips 3.2] interl
3.2 wound] after del ‘would’
3.2 French] above del ‘french’
3.4 is] interl
1
The month and year are established by the relationship between this letter and the letter to J. D. Hooker, 1 July 1878.
2
CD had asked to borrow a Porlieria hygrometrica plant from the Royal Botanic Gardens at Kew (see letter to J. D. Hooker, 1 July 1878). A plant was sent to Down on 5 July 1878 (Outwards book, p. 463, Archives, Royal Botanic Gardens, Kew). On the status of the name Porlieria hygrometrica, see the letter from Francis Darwin, [22 June 1878] and n. 6.
3
John Ferguson McLennan was expected to visit Down on Friday 5 July 1878 (see letter to O. C. Marsh, 2 July 1878). His visit may have been postponed until 6 July. CD’s notes on radicles of Zea mays (maize), dated between 2 and 8 July [1878], are in DAR 209.5: 208–19; the experiments are described in detail in Movement in plants, pp. 178–81.
4
CD found that temperatures above 70°F destroyed the sensitivity to irritation of bean (Vicia faba) radicles (Movement in plants, p. 142), but that radicles of maize increased in sensitivity in temperatures varying from 76 to 82°F. (ibid., p. 178). According to CD’s definition, an organ could be called sensitive when its irritation excited movement in an adjoining part (ibid., p. 191); in experiments where a piece of card was attached to one side of the root tip, CD found that the root bent away from the irritation of the card. Maize was highly sensitive at optimal temperatures, and was the only monocotyledon on which CD and Francis experimented (ibid., pp. 177–9). Beans are dicotyledons.