skip to content

Darwin Correspondence Project

From Francis Darwin   [4–7 August 1878]1

Botanisches Institut | Würzburg

My dear Father,

I ought to have seen the place about Akebia & Stauntonia, also I should think your explanation is quite as good as Sachs, or rather better as it explains the appearance without assuming any new cause.2 I had so few Helvingia to work with I couldn’t try whether anything comes out of them.3 Sachs gave me all the berries on the bush but it was too late. The difference in rate of drying is very well marked. Also 3 of the cleaned ones which I have wetted by squirting water over them have mould growing on them. Sachs said they tried some experiments about the growth of mould on fruit, by sowing mould spores on fruit & they found that the mould grow far better on the fruit grapes & apples which has been wiped. He seems to think it very important to make out whether water dissolves anything out of leaves, but he thinks the way of weighing would be no good, as not being delicate enough— He says that if you water a plant with lithium solution & then put the leaves in water the lithium comes out. I have tried here with a tobacco plant & it is quite easy to do & lots of lithium came out.4 He thinks it would be a good way of trying cleaned & bloom leaves, though not absolutely convincing as you don’t know whether the lithium is in a natural state in the cell sap.

He says he has found dew alkaline which he supposes is from the potash coming out, & thinks that also worth trying. I had thought of the lithium way with bloom & cleaned, but thought it too imaginary a way. He suggests a a way of testing whether nitrogenous stuff comes out, to infect the water in which cleaned & bloom leaves have soaked with a drop or two of bacterial fluid.5 I wish I had thought of this before, as I have had very little to do for the last 10 days & I might have tried it. There is a wild Lactuca here that has leaves which slew so that the edges are up & down a vertical as they grow up, I find it has nearly as many stomata on the upper as on the lower side like an Australian tree.6 It has bloom on both sides. I will bring some seed as it might do for comparison somehow with sleepers as its leaves are vertical. I think one might test the nitrogen in water from cleaned leaves with Drosera7   I have given your message to Sachs & he seemed much pleased & said that he was much obliged, & that Down was the first place he would wish to go to, if he manages to come through London8

I suppose you have got my letter saying I shall be at Leith Hill Thursday afternoon—9

Yr affec. | F. D.

CD annotations

1.1 I … cause. 1.3 crossed blue crayon
1.3 I had … marked. 1.5] ‘Bloom Helvingia.’ blue crayon
1.9 He … sap 1.16.] ‘Frankland wd test for nitrogenous matter’10 blue crayon
2.3 He suggests … Drosera 2.11] ‘There is some way of testing for ammonia’ blue crayon
2.12 I have … afternoon— 3.2] crossed blue crayon


The date range is established by the relationship between this letter and the letter to Francis Darwin, 3 August [1878], and by the reference to Francis’s planned arrival at Leith Hill Place (see n. 9, below). In 1878, the Thursday following 3 August was 8 August.
Akebia (the genus of chocolate vine) and Stauntonia are in the family Lardizabalaceae, formerly a division of the Menispermaceae. Julius Sachs, having observed corkscrew-like contraction of shoots of Menispermum (the genus of moonseed), had suggested that it would be easy to show the similarity of twining and tendril-bearing climbers (letter from Francis Darwin, [before 3 August 1878]). CD suggested that the contraction was more likely to be connected to slow growth or ill health (see letter to Francis Darwin, 3 August [1878] and n. 2).
Francis was conducting experiments on Helvingia rusciflora (a synonym of Helwingia japonica); he was evidently attempting to determine whether any substance might be exuded from the petals (see letter from Francis Darwin, [21 July 1878]).
Francis was trying to work out the function of bloom, the waxy or pruinose coating on some leaves and fruit, and was experimenting with the berry-like drupes of Helwingia. Sachs had developed the lithium method for determining rates of transpiration in plants (see Sachs 1878, pp. 163–6).
In 1872, Ferdinand Julius Cohn had described the role of bacteria in putrefaction; he had determined that bacteria split up albuminous compounds into ammonia or nitric acid and other products, and assimilated the ammonia. Water with a nitrogeneous solute to which a few drops of bacterial fluid had been added would become cloudy and later form a bacterial precipitate (Cohn 1872, pp. 45–6). Sachs evidently assumed that bacteria would multiply in the presence of nitrogenous compounds in the water in which the leaves had been soaked.
Lactuca is the genus of lettuces. Francis evidently refers to Lactuca serriola (prickly lettuce or compass plant); the upper leaves twist round to hold their edges upright in sun. Australian tree genera such as Eucalyptus and Acacia typically have stomata on both upper and lower leaf surfaces.
Drosera is the genus of sundews.
CD had extended an invitation to Sachs to visit him at Down (see letter to Francis Darwin, 25 July [1878]).
The letter has not been found. Leith Hill Place was the home of CD’s sister, Caroline Sarah Wedgwood, and her family; the Darwins visited there from 7 to 12 August 1878. Francis planned to join them on Thursday 8 August; he returned to Down on 12 August (Emma Darwin’s diary (DAR 242)).
Edward Frankland often assisted CD with chemical aspects of his research; he had perfomed several experiments on CD’s behalf when CD was working on Insectivorous plants (see Correspondence vols. 21 and 22).


Cohn, Ferdinand Julius. 1872c. Über Bacterien und deren Beziehungen zur Fäulniss und zu Contagien. [Read 14 February 1872.] Jahres-Bericht der Schlesischen Gesellschaft für vaterländische Cultur 50: 44–7.

Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 28 vols to date. Cambridge: Cambridge University Press. 1985–.

Insectivorous plants. By Charles Darwin. London: John Murray. 1875.

Sachs, Julius. 1878. Ein Beitrag zur Kenntniss des aufsteigenden Saftstroms in transpirirenden Pflanzen. Arbeiten des Botanischen Instituts in Würzburg 2 (1878–82): 148–84.


Experiments on effects of removing "bloom" from leaves and fruit.

Letter details

Letter no.
Francis Darwin
Charles Robert Darwin
Sent from
Botanisches Institut, Würzburg
Source of text
DAR 162: 57
Physical description
ALS 4pp †

Please cite as

Darwin Correspondence Project, “Letter no. 11632,” accessed on 25 June 2022,