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Darwin Correspondence Project

From W. T. Thiselton-Dyer   11 May 1878

Royal Gardens Kew

May 11. 78

Dear Mr Darwin

Our indefatigable Lynch has taken your wants in hand and we will do the very best we can for you. It is good of you to let us supply you as of course it is honour and glory to us.1

I have not seen the paragraph in the Times but it must have sharply perverted what I said.2 It is always so with reporters; they have no genuine desire to understand one’s meaning and are too indifferent to make careful notes or ask for explanations afterwards if one’s meaning is not clear to them.

I certainly stated that the heliotropism of plants is something independent of the advantage gained by green plants moving towards the light though that movement is due to it. I deduce this statement—which I fear is not quite clear—from Vines’s work on the slowing effect of light on a hypha of Phycomyces which has no chlorophyll of course and therefore could gain nothing by heliotropism3   He attributes this “slowing” to a paralysis of the protoplasm produced by light preventing the extension of the contiguous cell wall. The protoplasm loses extensibility, the cell wall in intimate contact with it does the same. hence growth is locally arrested. Hence also on a large scale the multicellular plant curves over towards the light. This is undoubtedly in a green plant an advantage to it but I am so far heretical as to feel doubtful whether, from the facts, one can affirm that the advantage of heliotropism has brought it about. It appears to be a habit which plant-protoplasm contracted before it learned the chlorophyllian process. I offer this view with all possible submission— I think it is not the same thing quite as denying the advantage of heliotropism.

Your son Frank came down to see me and spent a most agreeable afternoon. He told me about the roots.4 I am immensely interested   When you were at Kew I pointed out to you a very characteristic Example of positive heliotropism in the aerial roots of an orchid. The plant was one brought by Moseley from the Admiralty Islands.5 But I dare say with a little management we could get other less valuable specimens to show the same thing.

I am going away with my wife for a few days to the seaside6 and perhaps when you return to Down

CD annotations

1.1 Our … them. 2.4] crossed pencil
4.1 Your son … interested 4.2] crossed pencil
4.3 Example … an orchid 4.4] double scored pencil
Top of letter: ‘Heliotropism very good’ ink; ‘[‘If an evi’ del] If turning to light an evil can be checked & this process, however effected cd be increased till opposite result gained | Plants vary so much in degree of Heliotropism & even individuals the cases endlessly variable’ pencil


See letter to W. T. Thiselton-Dyer, 9 May [1878] and nn. 2 and 4. Richard Irwin Lynch was foreman of the propagating department at Kew.
Sydney Howard Vines had studied the influence of light on Phycomyces nitens (common pin mould) while studying at Julius Sachs’s laboratory in Würzburg. His experimental results were reported in Vines 1878.
The date of Francis Darwin’s visit has not been established. Francis was assisting CD in experiments on the sensitivity of radicles (embryonic roots). CD had mentioned their findings in his letter to Thiselton-Dyer of 9 May [1878].
CD had visited Kew on 22 January 1878 (letter to Asa Gray, 21 [and 22] January 1878). Henry Nottidge Moseley collected the orchid specimen while employed as a naturalist on the Challenger expedition. Orchids collected in the Admiralty Islands were described in the botany section of the report on the scientific results of the voyage (Hemsley 1885–6, 1 (IV): 247–8).
Harriet Anne Thiselton-Dyer (see letter to W. T. Thiselton-Dyer, 9 May [1878] and n. 6).


Hemsley, William Botting. 1885–6. Report on the scientific results of the voyage of H.M.S. Challenger during the years 1873–76 (Botany). 2 vols. London: HMSO.

Vines, Sydney Howard. 1878. The influence of light upon the growth of unicellular organs. Arbeiten des botanischen Instituts in Würzburg 2 (1878–82): 133–47.


WTT-D’s statement perverted by Times [4 May 1878, p. 6, on WTT-D’s Royal Institution lectures on vegetable morphology].

S. H. Vines’s work on light inhibition of Phycomyces hyphae ["The influence of light upon the growth of unicellular organs" (1878), Arb. Bot. Inst. Würzburg 2 (1882): 133–47] suggests heliotropism in green plants is independent of, and more primitive than, photosynthesis.

Heliotropism in aerial roots.

Frank Darwin’s work.

Letter details

Letter no.
William Turner Thiselton-Dyer
Charles Robert Darwin
Sent from
Source of text
DAR 209.8: 154
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 11503,” accessed on 10 April 2021,