Mast, Light Reactions in Lower Organisms. 



139 



in light intensity from 142 candle meters to 380 candle meters 

 causes an average decrease in deflection of i| degrees. 



By referring to the above tables and text figures it will be noted : 

 (i) that Volvox, in swimming horizontally toward a source of 

 light, seldom moves parallel with the rays. There is striking 

 individual variation in the angle of deflection, the variation in 

 these experiments being from 16 degrees to the left to 24 degrees 

 to the right; (2) that in a field of light graded in intensity there is 

 a tendency to deflect toward the brighter end of the field, an 



Fig. 8. Graphic representation of the total average difference in deflection due to difference in light 

 intensity on opposite sides of the colonies, as indicated in Tables II and III. a, plate glass aquarium 

 8 cm. wide and 15'cm. long; h, light rays; c, c' points where the colonies were introduced; d, average 

 course with the region of highest light intensity to left; e, average course with strongest illumination 

 to the right. Light intensity at (/) the middle of field 57.11 candle meters. From the middle the 

 intensity gradually increased toward either end where it was 442.68 candle meters. Intensity at c, 327 

 candle meters, at c', 263 candle meters. 



average of over i^ degrees under the conditions of these experi- 

 ments; (3) that the degree of deflection in a field of light graded in 

 intensity depends upon the strength of illumination, it being 

 greater in a low light intensity than in a high one. A decrease in 

 intensity from 380 candle meters to 142 candle meters without 



