To J. S. Henslow   11 October [1860]

15 Marine Parade | Eastbourne

Oct 11.

My dear Henslow

Very many thanks for your pleasant letter just received from Down, with many things which interested me.1 I am particularly obliged for answer about contracting & expanding red thick fluid substance. I have been observing it with great care. & it really is a most curious phenomenon.—   It all takes place within the same cell. & is, I now find certainly not from endosmose or exosmose from any external fluid;2 for a hair cut off & put dry between two slips of glass, shows the phenomenon splendidly. I have outline of a whole series of changes; which are infinitely varied & never cease. The movement can never be seen until after the hairs have contracted over a Fly or other substance.3 But I shall write a paper on the subject: so will not trouble you any more.—

You have told me what I wanted to know, whether it was some well phenomenon.—4

Yours affect | C. Darwin

Dr. Bree “pitches” into me handsomely.—5

Endorsement: ‘1860’

1
Henslow’s letter has not been found. It was evidently a reply to the letter to J. S. Henslow, 28 [September 1860].
2
CD discussed the phenomenon of ‘aggregation’ in Insectivorous plants, chapter 3. He stated that at first he believed the ‘movements of the masses might be due to the absorption of water’ (ibid., p. 41).
3
CD later found that the process of aggregation was independent of the inflexion of the hairs (ibid., pp. 43, 54–5).
4
Henslow interlined ‘known’ after ‘well’.

Manuscript Alterations and Comments

1.3 fluid] interl
1.4 the same] above del ‘one’
1.8 The movement] above del ‘They’
1.8 be] above del ‘have’

Please cite as “DCP-LETT-2945,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-2945