From Francis Darwin   9 July 1879

Bot Institut Würzburg—

July 9. 79

I have tried touching a hair of Tradescantia under the microscope but it produces no effect: Then I tried pressing on the cover glass & it requires strong pressure to produce any effect, & then the streaming protoplasm is paralysed & remains still for a few minutes & then goes on again.1 Hofmeister says the same thing in his Lehre von der Pflanzenzelle (Handbuch Phys Botanik Bd 1 erster Abtheilung p 50;) the book is in the study on a shelf over the yard measure (it is catalogued I think).2 I will try Drosera both aggregated & not. If the protoplasm in a cell which lines the cell wall & whose duty it is to look after the tension of the cell is also paralysed one would expect movement to occur—3 Very glad about H have written to him—4

F D.

Caustic mustards grew as much as the not caustics & were aphelic again today5

ApcS

1
Francis evidently refers to the stamen hairs that characterise flowers of some species of Tradescantia (the genus of spiderwort). Ferdinand Julius Cohn, after reading Insectivorous plants, had drawn CD’s attention to these hair cells, noting that the protoplasm adhering to the cell walls was colourless, while the blue fluid of the central vacuole was not protoplasm. Based on his observation that the pigments were insoluble in protoplasm, Cohn queried whether the red aggregated matter that CD had described in Drosera (the genus of sundews) was protoplasm (see Correspondence vol. 23, letter from F. J. Cohn, 21 August 1875 and nn. 3 and 7). In the letter to Francis Darwin, 24 June [1879], CD had suggested that Francis try touching a cell to see whether it influenced the current of protoplasm.
2
Wilhelm Hofmeister had observed individual cells of the stamen hairs of Tradescantia virginica (a synonym of T. virginiana, Virginia spiderwort); he noted that moderate squeezing of the stamen filament resulted in an immediate cessation of movement of the streams of protoplasm, which then separated and formed little balls or club-shaped masses, sometimes together with protoplasm from the proximity of the nucleus, other times with the primordial utricle (the protoplasm lining the cell wall; see Hofmeister 1867, pp. 50–1).
3
In Insectivorous plants, p. 43, CD had observed that if the glands of the tentacles of Drosera were crushed between pincers the tentacles did not become inflected or exhibit any signs of aggregation, and seemed paralysed.
4
Horace Darwin had recently met with Thomas Henry Farrer, who had earlier objected to his proposed engagement to Ida Farrer (see letter to G. H. Darwin, 8 [July 1879] and n. 4).
5
See second letter to Francis Darwin, 2 July [1879]. Francis’s results regarding growth in roots of Sinapis alba (white mustard) whose tips had been cauterised confirmed that the use of lunar caustic (silver nitrate) did not cause systemic injury to the root as had been suggested by Julius Sachs (see letter from Francis Darwin, [before 26 June 1879]).

Please cite as “DCP-LETT-12142,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-12142