114 GEOEGB JOHN EOMANES I88I 



I remain ever yours, very sincerely and most 

 respectfully, ^^^_ j Eomanes. 



From C. Darwin, Esq., to G. J. Bomanes. 



Down : April 18, 1881. 



I am extremely glad of your success with the 

 flashing light. If plants are acted on by light, like 

 some of the lower animals, there is an additional 

 point of interest, as it seems to me, in your results. 

 Most botanists believe that light causes a plant to 

 bend to it in as direct a manner as light affects 

 nitrate of silver. 



I believe that it merely tells the plant to which 

 side to bend, and I see indications of this behef 

 prevailing even with Sachs. Now it might be 

 expected that light would act on a plant in some- 

 thing the same manner as on the lower animals. As 

 you are at work on this subject, I will call your 

 attention to another point. Wiesner, of Vienna (who 

 has lately published a good book on Heliotropism) 

 finds that an intermittent light during 20 m. produces 

 same effect as a continuous light of same brilliancy 

 during 60 m. So that Van Tieghem, in the first part 

 of his book, which has just appeared, remarks, the 

 light during 40 m. out of the 60 m. produced no effect. 

 I observed an analogous case described in my book. 

 Wiesner and Tieghem seem to think that this is 

 explained by calling the whole process ' induction,' 

 borrowing a term used by some physico-chemists (of 

 whom I believe Eoscoe is one), and impljdng an 

 agency which does not produce any effect for some 



