33 'POWER OF MOVEMENT [1878.. 



work." At this time he was studying the movements of 

 cotyledons, in which the sleep of plants is to be observed in 

 its simplest form ; in the following spring he was trying to> 

 discover what useful purpose these sleep-movements could 

 serve, and wrote to Sir Joseph Hooker (March 25th, 1878) : 



" I think we have proved that the sleep of plants is to lessen, 

 the injury to the leaves from radiation. This has interested 

 me much, and has cost us great labour, as it has been a 

 problem since the time of Linnaeus. But we have killed or 

 badly injured a multitude of plants : N.B. Oxalis carnoscv 

 was most valuable, but last night was killed." 



His letters of this period do not give any connected account 

 of the progress of the work. The two following seem worth, 

 giving as being characteristic of the author :] 



C. Darwin to W. Thiselton Dyer. 



Down, June 2, 1878. 



MY DEAR DYER, I remember saying that I should die a. 

 disgraced man if I did not observe a seedling Cactus and 

 Cycas, and you have saved me from this horrible fate, as they 

 move splendidly and normally. But I have two questions to 

 ask : the Cycas observed was a huge seed in a broad and 

 very shallow pot with cocoa-nut fibre as I suppose. It was 

 named only Cycas. Was it Cycas pectinata ? I suppose that 

 I cannot be wrong in believing that what first appears above 

 ground is a true leaf, for I can see no stem or axis. Lastly, 

 you may remember that I said that we could not raise 

 Opuntia nigricans ; now I must confess to a piece of stupidity ; 

 one did come up, but my gardener and self stared at it, and 

 concluded that it could not be a seedling Opuntia, but now that 

 I have seen one of O. basilaris, I am sure it was ; I observed 

 it only casually, and saw movements, which makes me wish. 



