Mast, Light Reactions in Lower Organisms. 133 



eral trials were made under each light condition and each path, 

 as recorded in the table below and in Fig. 7, is the average of sev- 

 eral such trials. There was, however, surprisingly little variation 

 in the direction of motion of different groups when subjected to the 

 same light condition. The light intensity was measured with care. 

 Both glowers were on the same circuit so that variation in voltage 

 could not have affected markedly the relative intensity of the light 

 from the two sources. There can thus be no question about the 

 approximate accuracy of the experiments, the results of which will 

 be readily understood by referring to Table I, in connection with 



Fig- 7- 



TABLE I. 



I. II. . III. 



82.4 candle meters. .o candle meters. o degrees. 



82.4 candle meters. 6.0 candle meters. 9 degrees. 



82.4 candle meters. 23.5 candle meters. 25 degrees. 



82.4 candle meters. 89.0 candle meters. 47 degrees. 



82.4 candle meters. 318.8 candle meters. 59 degrees. 



Table I represents the effect of light from two sources on the 

 direction of movement of Volvox. Column i gives the light inten- 

 sities at the middle of the light area in the aquarium, which were 

 produced by the 222 volt glower under the five different condi- 

 tions. Column II gives light intensities produced by the no 

 volt glower, and column iii the angles between the rays produced 

 by the 222 volt glower and the course taken by the organisms under 

 the different light conditions. 



In these five experiments the direction of the rays from the two 

 sources of light was practically constant, but the direction of 

 movement of the Volvox colonies varied 50 degrees. This varia- 

 tion was certainly not primarily due to any influence of the ray 

 direction; for when the relative intensity of light affecting different 

 sides of the organism was changed the orientation changed, thougn 

 the direction of the rays remained the same. It can, therefore, 

 be considered fully demonstrated that difference in light intensity 

 on different sides of the colonies may determine orientation inde- 

 pendently of the direction of the rays. Additional proof of this con- 

 clusion will be given later, in experiments of a different character. 



This conclusion is not in harmony with the dictum of Loeb, 

 repeatedly expressed in a recent work (1905), in which he writes, 

 "It is explicitly stated in this and the following papers that if there 

 are several sources of light of unequal intensity, the light with the 

 strongest intensity determines the orientation and direction of 



