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Darwin Correspondence Project

To Francis Darwin   7 [July 1878]1

Down, | Beckenham, Kent. | Railway Station | Orpington. S.E.R.


My dear F.

Porliera went beautifully to sleep in my study & awoke well early in the back & obscure part of my study, & has kept awake all day under skylight: it has circumnutated in simple manner.— Now I shd like to hear whether it is kept hot & dry at Würzburg; for it seems an odd case.— I will look to stomata some day.—2

Maize radicles have behaved splendidly & George has made some capital sketches. On other hand radicles of Cotton-plant almost always utterly insensible to the little sq.— I suppose I cannot get right temperature or keep air damp enough.

I wish I cd get some cement which wd hold under water.3

I have been looking to day at flowers of the Marantaceous Thalia dealbata:4 they wd be well worth investigating; if you pass bristle down young flower, & you then hear a click & the pistil shoots across the flower & becomes wound up like a corkscrew & seizes bristle; but when bristle withdrawn it is covered with pollen.— I think pistil is held straight by a fold in a stiff petal, & slightest touch releases it, & then bang it goes off, ensuring cross-fertilisation.

Good bye, as I have nobody to talk to, about my work, I scribble to you.—

I send Nature.5

All the family are here & all adoring Bernard6

C. D.

I forgot to thank you for extract from Cieleski & about Sachs & sleeping plants.— Notwithstanding what he says, I shd. like to see sections, on your return, of bent & straight oats-cotyledons.7

CD annotations

1.3 Now … Wùrzburg; 1.4] underl red crayon


The month and year are established by the reference to the plant that CD had received from Kew (see n. 2, below).
CD was sent a plant of Porlieria hygrometrica from the Royal Botanic Gardens, Kew, on 5 July 1878 (see letter to Francis Darwin, 6 [July 1878] and n. 2). Francis had reported that Sachs did not understand its movements and believed it to be almost always asleep (see letter from Francis Darwin, [22 June 1878] and n. 6). CD may have wanted to check the location of the stomata in relation to leaf movement caused by changes in the moisture level; earlier authors had differed on whether the species was sensitive to such changes (see, for example, Fée 1858, pp. 467–9).
CD was testing the sensitivity of radicles (embryonic roots) by attaching tiny squares of card to one side of the tip; in optimal conditions, the roots moved away from the card, thus confirming their irritability (see letter to Francis Darwin, 6 [July 1878] and n. 4). Getting the pieces of card to stay in place was a challenge; CD later found that sandpaper adhered more effectively (Movement of plants, p. 133). George Howard Darwin’s sketches of the roots of maize (Zea mays) are in DAR 209.5: 200–3. In Movement of plants, p. 8, CD acknowledged George’s help with illustrations.
Thalia dealbata (powdery alligator-flag) is in the family Marantaceae (arrowroot) but CD described it as in the Cannaceae (Movement of plants, p. 389); it is native to North America. CD’s notes on movement of the pistil in flowers of T. dealbata, dated from 9 to 20 July [1878], are in DAR 209.13: 1–11.
The journal Nature was published weekly.
Bernard Darwin was Francis Darwin’s son; he had lived with CD and Emma Darwin at Down House since the death of his mother, Amy Darwin, in September 1876. William and Sara Darwin were visiting at the time of this letter (Emma Darwin’s diary (DAR 242)).
See letter from Francis Darwin, [before 7 July 1878] and n. 5. Francis had sent a work by Theophil Ciesielski and mentioned that Sachs did not think work in cutting sections of cotyledons to determine whether cells on the concave side of a bent stem were smaller than those on the convex side would give worthwhile results.


Fée, Antoine. 1858. Notice sur les plantes dites sommeilantes, et en particulier sur le Porlieria hygrometrica R. et Pav. [Read 13 July 1858.] Bulletin de la Société botanique de France 5: 451–71.


Describes sleep movements in Porlieria and his experiments on movements of radicles.

Thalia flowers have interesting mechanism to ensure cross-fertilisation.

Letter details

Letter no.
Charles Robert Darwin
Francis Darwin
Sent from
Source of text
DAR 211: 34
Physical description
4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 11595,” accessed on 14 June 2021,