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Darwin Correspondence Project

From Francis Darwin   [before 17 July 1878]1

Botanisches Institut | Würzburg

My dear Father

Here are some more sleepers2

Oxalis latifolia like Acetisella

O. variabilis— ditto but has 4 leaflets

Lotus Gebelia sleeps like a Lotus

Erythrina spathacea— an end leaflet & 2 lateral ones which all drop vertically

E. princeps— ditto

Albizzia Zulu brizzia, like A lopantha

Bauhinia discolor; the leaf is not quite divided into two leaflets but is so diagram but shuts upwards lik B. Richardiana. This plant looks very sick & shuts up very badly, but B. forficata has similar leaves & shuts up well.

Cassia glauca— {like a Cassia outside in

Uraria lagopus (Leguminosæ) end & 2 lateral leaflets drop down vertically not outside-in, but simply   Leaflets grow so close together & are so thick that they looked asleep but are not altered by day

Coesalpina echinata shuts upwards 3

Sachs idea about climbing plants is something like this. He thinks one ought to distinguish clearly between the revolving nutation (which is only in order to find a support as you say) & the growth which goes on when the shoot has once caught a support.4 With a tendril the difference is quite clear, the tendril swings round till it finds a support & then all the growth (or alteration in length from altered tension) is concentrated on one side & the tendril curls up. When a twining shoot has wound round a support as far as it can, it would be much more economical of it to confine the most rapid growth to the outside only. Both cases seem to me capable of fitting in with your theory of circumnutation ceasing when the plant wants to bend in a special direction   I can’t find in your book an experiment in which the nutation ceased when a plant was turned up side down, I thought that nutation ceased in order to let all the growth to turn into geotropism.5 Your theory ought to be called the conservation of energy—I believe it will be splendid. I should like to know if you made many observations as to whether tendrils are geotropic or not, most seem not to be much so. Perhaps I havn’t read your book carefully enough, you often say that the circumnutation is in order to find a support, but you dont distinguish the growth afterwards I think. There is one machine we must have. A strong horizontal axis about 2 feet long which goes round by clock work slowly so that geotropism is quite excluded. We will get Jemmy to design one, the one here is far from well made.6

I am rather surprised at the results of my experiments on bendibility of grass stalks. If you take the cylindrical flowering stalk of grass while still green & keep it 2 or 3 days till the protoplasm in it is certainly dead, then if you test its bending strength as it is & then when it is saturated with water, it is always stronger in the wet state   But ripe white stalks which have been in the laboratory for years are always stronger dry   The same thing seems to hold with wood freshly cut sticks are stronger wet, old dry sticks are stronger dry.7

There have been several days heavy rain & now the Porliera in the flower bed is as open as the one in the pot. I will get the pot one in & keep it dry & see. I will have a look at the stomata, only I don’t know quite whether you mean the number of them or what. I cut some sections & the cuticle is decidely thick I should say—8

I find that if an already twined plant is turned upside down the last turn unwinds itself—did you ever see this. I forgot to say how glad I am the maize act so well— I like hearing about yr work v much—9

Yr affec son | Francis Darwin

Please remember the printing machine— Tho’ I have no doubt that you have an enormous pincers with a small bit of paper & ‘printing machine’ written in red pencil10

CD annotations

1.1 Here are … a Lotus 4.1] crossed pencil
3.1 O. … leaflets] scored red crayon
5.1 Erythrina … ditto 6.1] crossed pencil
9.1 Cassia glauca … in] crossed pencil
11.1 shuts upwards] ‘Porliera in open ground after several days of rain as open or awake as the plant in pot.—’ ink crossed pencil
12.1 Sachs … grass stalks. 13.2] crossed blue crayon; opening square bracket red crayon
12.1 Sachs … support. 12.4] crossed pencil
17.1 Please … red pencil 17.2] crossed red crayon and pencil
Top of letter: ‘Received July 17think circled ink


The date is established by the relationship between this letter and the letter to Francis Darwin, 17 July [1878].
Francis had recently sent CD a list of plants that slept (letter from Francis Darwin, [12 July 1878]).
Oxalis latifolia (broadleaf wood sorrel), O. acetosella (a synonym of O. montana, mountain wood sorrel; Acetisella is a misspelling), and O. variabilis (a synonym of O. purpurea, purple wood sorrel) are in the family Oxalidaceae. Lotus gebelia, Erythrina spathacea (a synonym of E. variegata, tiger’s claw), E. princeps (a synonym of E. humeana, dwarf erythrina), Albizia julibrissin (silktree; Zulubrizzia is a misspelling or incorrect epithet), A. lopantha (a synonym of Paraserianthes lophantha, plume albizia), Bauhinia discolor (an unknown combination, but may refer to B. pauletia, whose bat pollinator is Phyllostomus discolor), B. richardiana, B. forficata (Brazilian orchid tree), Cassia glauca (a synonym of Senna surattensis ssp. sulfurea, smooth senna), Uraria lagopus, and Caesalpinia echinata (Brazilwood) are in the family Leguminosae (a synonym of Fabaceae, peas and beans).
Julius Sachs had asked Francis to determine whether tendril-bearers and twiners behaved in the same way (letter from Francis Darwin, [12 July 1878]).
In Climbing plants 2d ed., p. 98, CD noted that in Bignonia capreolata a slow inclination from light to dark occurred at the same time as the tendrils revolved; after the revolving movement had ceased, successively formed tendrils continued to bend in the direction of shade regardless of where the plants were positioned. Geotropism is tropic or directional movement in response to gravity.
The klinostat, a rotating plant-holder used to test the influence of gravity, was invented by Sachs (Pringsheim 1932, p. 225); the version developed by Horace Darwin (Jemmy) is described in detail and with several diagrams in F. Darwin 1880, pp. 449–55 (see plate on p. 296).
The purpose of these experiments was to determine the extent to which the stiffness of a stem was due to the tension of the cell walls (letter from Francis Darwin, [22 June 1878]).
Francis had observed that a Porlieria twig in water kept its leaves open, while a plant growing in dry conditions had shut leaves (see letter from Francis Darwin, [29 June] 1878 and n. 3). He later noticed morphological differences between the Würzburg plants and a twig from one sent from Kew, as well as differences in their responses to moisture and light (see letter from Francis Darwin, [after 7 July 1878] and n. 3). CD found the difference in behaviour odd and told Francis he hoped to look at the stomata of his specimen (letter to Francis Darwin, 7 [July 1878]).
CD had reported his success in testing the sensitivity of the tips of maize radicals (letter to Francis Darwin, 7 [July 1878] and n. 3).
CD had suggested giving his typewriter to Carl Gottfried Semper but wanted the machine to be cleaned and packed by the makers (letter to Francis Darwin, 14 July [1878]). Francis wrote the comment at the top of the first page of the letter.


Climbing plants 2d ed.: The movements and habits of climbing plants. 2d edition. By Charles Darwin. London: John Murray. 1875.

Pringsheim, Ernst Georg. 1932. Julius Sachs: der Begrunder der neueren Pflanzenphysiologie. Jena: Gustav Fischer.


More sleepers from green-house.

Julius Sachs’s view of climbing plants: he distinguishes between nutation to find a support and growth after support is found.

Letter details

Letter no.
Francis Darwin
Charles Robert Darwin
Sent from
Source of text
DAR 209.1: 155; DAR 274.1: 50, 52
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 11613,” accessed on 1 July 2022,