From J. I. Rogers to Francis Darwin 25 March 1878
119, Cannon Street, | London, | E.C.
25th. March 1878
Dear Sir,
Referring to your lecture on the “Analogies between Animal & plant life” and to the use of the movements of the Sensitive plant not having been accounted for—1 my attention was directed to this subject by Dr Darwins book on climbing plants,2 & from some very rough experiments, I was led to the conclusion that the movements of the Sensitive plant were protective agains⟨t⟩ insect depredations. I am, to my great loss, not a botanist & therefore what follows may be well known to you in which case I must apologize for taking up your time.
On raising some sensitive plants in an in⟨n⟩er con⟨ser⟩vatory case together with some other seeds, I found that all the plants from the latter were much injured by woodlice while the Sensitive plants were untouched. On putting caterpillars & slugs on to the stem of the full grown Sensitive plants, I found that the down pointing thorns caused them such annoyance that they could hardly be forced to climb up. On placing them on the leaves or branches, the movements ⟨caus⟩ed the caterpillars much ⟨in⟩convenience & apparently frightened them, so that they generally dropped off as soon as they could. If not they remained quite still & if left on at night they had disappeared by morning leaving the plant untouched. Sometimes t⟨he⟩ caterpillar got on to the flower which is apparently not sensitive & then began to browse at ease. When the caterpillar remained on the branchlet & the leaves closed up, they presented a hard edge with hairs or thorns so as to increase the difficulty of eating them.3 A bee alighting on the leaves & finding them yield would naturally settle on the flower—thus promoting fertilization.
An Indian friend told me that on brush⟨ing⟩ through an inviting looking green patch of Sensitive plants they suddenly move & the leaves disappear, leaving exposed the horribly sharp thorns which clothe the join⟨ts⟩ of the stems. This may be protective as a⟨g⟩ainst g⟨ra⟩zing animals; for the thorns like those of furze or brambles in waste places, would be unattractive, & the disappearance of the leaves would divert the animals’ attention.
Perhaps the leaf motions of the Indian “Telegraph plant” (botanically called Desmodium gyrans I believe)4 may shoot off insects.
Believe me to be dear Sir | Yours faithfly | J Innes Rogers
⟨Fra⟩ncis Darwin Esq.
CD annotations
Footnotes
Bibliography
Climbing plants 2d ed.: The movements and habits of climbing plants. 2d edition. By Charles Darwin. London: John Murray. 1875.
Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.
Movement in plants: The power of movement in plants. By Charles Darwin. Assisted by Francis Darwin. London: John Murray. 1880.
Summary
Suggests movements of sensitive plants may protect against insects.
Letter details
- Letter no.
- DCP-LETT-11445
- From
- John Innes Rogers
- To
- Francis Darwin
- Sent from
- London, Cannon St, 119
- Source of text
- DAR 176: 196
- Physical description
- ALS 4pp † (by CD)
Please cite as
Darwin Correspondence Project, “Letter no. 11445,” accessed on 19 April 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-11445.xml