268 



LIGHT AND THE BEHAVIOR OF ORGANISMS 



reversed. This is clearly shown in the following observa- 

 tions on Volvox, graphically represented in Fig. 33. By 

 referring to path A it will be seen that the colony introduced 

 at n was positive to light from the three glowers as well as 



a 



0*0(7 



Fig. 33- The lines A and B represent the courses taken by single Volvox colo- 

 nies as seen in water 2 cm. deep in a plate-glass aquarium e. (The paths are rep- 

 resented in approximately accurate proportions); g, a group of three 222-volt 

 Nernst glowers in a vertical position; a, carbon arc; /, direction of light rays; d, 

 opaque screens; fin', path with glowers exposed and arc shaded; cc', path with arc 

 exposed and glower shaded; c'n, path with both glowers and arc exposed. 



to that from the arc, but that it became negative after 

 swimming toward the arc for a short distance from c, turned 

 about and moved across the aquarium to c'. That is, at 

 the end of the experiment the colony was negative to a 

 much lower light intensity than at the beginning. The 

 arc was approximately 250 candle power. It was 15 cm. 



