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Darwin Correspondence Project

To Francis Darwin   [1 August 1878]1

[Down.]

P.S. I have made yesterday & day before some observations which have surprised me greatly. The tendrils of Bignonia capreolata (as described in my book) are wonderfully apheliotropic, & the tips of quite young tendrils will crawl like roots into any little dark crevices. So I thought if I painted the tips black, perhaps the whole tendril wd be paralysed. But by Jove exactly the reverse has occurred; on 2 occasions the tendril with blackened tips became along its whole length curved to dark side of box, long before its fellow-tendril with naked tips!2 It looks as if the tips were like inhibitory nerve-ganglia, & when paralysed by being blackened allowed the rest of the tendril being immediately acted on; whereas the naked tips of the fellow-tendril prevented for a time the basal part of tendril obeying the action of light.— Or what is more probable the tips being blackened renders the basal part more sensitive to darkness. With the cotyledons of Phalaris & Avena blackening the tips rendered the basal part less or not at all sensitive to light.—3 I must somehow get more plants of Bignonia capreolata & find out whether whole observation is an error, or what on earth the case means.— It seems at present very odd. Last night the difference between the tendril with blackened tips & its fellow one was most conspicuous.—

Having no one to talk to, I scribble this to you.—

Footnotes

The date is established by the relationship between this letter and CD’s notes on Bignonia capreolata (see n. 2, below). This seems to be a postscript to a missing letter.
CD’s notes on blackening the tips of Bignonia capreolata, dated 27 July to 1 August 1878, are in DAR 209.8: 37–8; CD came to the conclusions he repeats in this letter on 31 July. Undated notes on the tendrils of Bignonia capreolata turning away from the light are in DAR 157.1: 141–2. CD alludes to Climbing plants 2d ed., pp. 98–9, in which he described experiments showing how tendrils of this species avoided light whenever possible.
CD’s undated abstract of his experimental results with Avena (the genus of oats) is in DAR 209.8: 26–8. His notes on Phalaris (canary grass) with tips blackened, dated 26–7 December 1877 and 1–8 January 1878, are in DAR 209.8: 73–6.

Bibliography

Climbing plants 2d ed.: The movements and habits of climbing plants. 2d edition. By Charles Darwin. London: John Murray. 1875.

Summary

Describes observations and experiments on the response to light of Bignonia capreolata tendrils.

Letter details

Letter no.
DCP-LETT-12077
From
Charles Robert Darwin
To
Francis Darwin
Sent from
unstated
Source of text
DAR 211: 52
Physical description
inc

Please cite as

Darwin Correspondence Project, “Letter no. 12077,” accessed on 19 April 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-12077.xml

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