BUNSEN-ROSCOE LAW 



85 



the time required for different intensities of light varying 

 from 0.00017 to 26,520 candle power to cause 50 per cent, 

 of the seedlings to show heliotropic curvatures. As can 

 be seen, the product it is always approximately 20. 



Ewald and the writer 300 > 305 tested the validity of the 

 law of Bunsen and Roscoe for the heliotropic curvatures 

 of Eudendrium. A number of stems of Eudendrium, 

 from which the polyps had been cut off, were put upright 

 into a trough with parallel walls, containing sea water. 

 As soon as the new polyps had regenerated they were 

 exposed to light of a certain intensity for a short time 

 and then kept in the dark. In the dark the bending of 

 the polyps in the direction of the former source of light 

 occurred. The purpose was to find the minimum time of 

 exposure required for a given light (40 candle power) 

 to induce 50 per cent, of the polyps to bend to the light 

 (Table IV). 



TABLE IV 



Percentage of polyps bending toward the former source of light 



1 Very young, abnormally sensitive polyps. 



