1881 FLASHING LIGHT ON PLANTS 115 



time, and continues its efifect for some time after the 

 cause has ceased. I believe (?) that photographic 

 paper is an instance. I must ask Leonard whether 

 an interrupted Hght acts on it in the same manner 

 as on a plant. At present I must" still beheve in my 

 explanation that it is the contrast between hght and 

 darkness which excites a plant. 



I have forgotten my main object in writing, viz. 

 to say that I beheve (and have so stated) that seedlings 

 vary much in their sensitiveness to Hght ; but I did 

 not prove this, for there are many difficulties, whether 

 time of incipient curvature or amount of curvature 

 is taken as the criterion. ^Moreover, they vary 

 according to age and perhaps from ^•igour of growth ; 

 and there seems inherent variability, as Strasburger 

 (whom I quote) found with spores. If the curious 

 anomaly observed by you is due to varpng sensitive- 

 ness, ought not all the seedlings to bend if the flashes 

 were at longer intervals of time ? According to my 

 notion of contrast between hght and darkness being 

 the stimulus, I should expect that if flashes were 

 made sufficiently slow it would be a powerful stimulus, 

 and that you would suddenly arrive at a period when 

 the result would suddenly become great. On the 

 other hand, as far as my experience goes, what one 

 expects rarely happens. 



I heartily wish you success, and remain, yours 

 ever very sincerely, 



Ch. Dakwin. 



Do you read the ' Times ' ? As I had a fair 

 opportunity, I sent a letter to the ' Times ' on Vivi- 



