326 GBOEGE JOHN EOMANES i893 



intermittent for the other set by working the flash 

 shutter ; in all cases the interrupted light caused, the 

 plants to start bending more quickly, and through a 

 greater angle in a given time. 



As regards the rate the flashes must succeed 

 one another to produce this heliotropic effect, Mr. 

 Eomanes found that sparks passed at the rate of fifty 

 in an hour would cause considerable bending in half 

 an hour. It is of interest to note that in no single 

 case was there any green colouring matter produced, 

 the seedlings remaining colourless even when the 

 sparks were passed at the rate of 100 per second 

 continuously during forty-eight hours. 



Dr. Sanderson writes : 



Friday, November 17. 



My dear Eomanes, — There was a rather interest- 

 ing discussion at the E.S. on your paper about the 

 fresh experiments with seedlings. It was objected 

 that there was no evidence that the effects were 

 not due to one-sided drying of the stems of the 

 seedlings, and wanted to know whether suffi- 

 cient precautions were taken to guard against this. 

 I suppose that he meant heat effects. I said that, 

 under the conditions of this experiment, I could 

 not see how any ' drying effect ' could possibly take 

 place. 



My suggestion is that it would be worth while 

 to add a note, if you think of the impossibility of 

 any effect, excepting a light effect, being concerned. 

 I asked Foster just now, and he agreed with me 

 that it would be useful. I ought to add that it 

 was admitted that the observation was a new one 

 which promised to have very important bearings. 



