25 JO 



Obser\/eaf 



Figure 101. Graphs showing the relation between the direction of locomotion ob- 

 served in a field of light produced by two horizontal beams crossing at right angles 

 and that demanded by the "Resultantengesetz." Abscissae, angles between the direction 

 of locomotion and the direction of the rays in the stronger beam observed with dif- 

 ferent ratios of intensities in the two beams, ranging from at 0° to 1 at 45° ; ordinates, 

 angles between the direction of locomotion and the direction of the rays in the stronger 

 beam demanded by the "Resultantengesetz." 3 Euglena rubra; O Gonium pectorale ; # 

 Volvox minor; O Volvox globator. (After Mast, 1907.) Note that if the observed 

 direction of locomotion were the same as the theoretical all the points would fall on 

 the broken line, and that this practically obtains for Euglena but not for Volvox and 

 Gonium. Note also that for the latter, as the ratio between intensity in the two beams 

 decreases from 1, the difference between the theoretical and the observed results in- 

 creases to a maximum, then decreases to zero, after which it increases in the opposite 

 direction. (After Mast and Johnson, 1932.) 



