8G 



TROPISMS 



If we calculate from this the value of the product it for 

 different intensities of light we find that it obeys the 

 Bunsen-Roscoe law (Table V). 



table v 



The material varies considerably so that it is not 

 always possible to induce 50 per cent, of the polyps to 

 undergo heliotropic curvature. For this reason Loeb 

 and Wasteneys 312 repeated these experiments by a some- 

 what different method. 



We confined our experiments to three intensities of 

 light by putting the specimens at distances of 25, 37.5, 

 and 50 cm. from a Mazda incandescent lamp, of about 33 

 Hefner candles. The times of exposure were adjusted so 

 that on the assumption of the applicability of the Bunsen- 

 Roscoe law the same effect, i.e., the same percentage of 

 polyps bending towards the light should be produced. 

 Thus in some experiments the exposure for the three dis- 

 tances given was 10, 22.5, and 40 minutes respectively, 

 in others, 7, 15.75, and 28 minutes, and so on. The ratios 

 of the percentage of polyps bending toward the light for 

 the three distances should be as 1 : 1 : 1. Since the material 

 differed widely in different experiments and in different 

 dishes, it was necessary to compute the averages of a 

 large number of experiments. 



The colonies, immersed in sea water, were arranged 



