HELIOTROPISM OF ANIMALS 13 



on the other hand. If the law had reference only to white light, 

 and not also to colored light red, blue, etc. which is, however, 

 by no means always the case, one might at first be inclined to be- 

 lieve that the animals which prefer red avoid mixed light because 

 it contains many of the hated short waves of the blue and violet 

 light; for this very reason it would be more agreeable than dim 

 light to the animals which prefer blue, for dim mixed light is poor 

 in all rays, and therefore also in blue. Yet the objection might be 

 raised against this explanation that mixed light contains as much 

 red for those animals which prefer red as it contains blue for those 

 animals which prefer blue. Yet this objection could again be 

 weakened by the assumption that, since the animals which prefer 

 red also prefer darkness, they prefer a minus of their chosen color 

 to a plus of the color they dislike. 



Graber finally considers it best "to await further investi- 

 gations in a field where great darkness still prevails." We 

 see that Graber in regard to the effects of monochromatic 

 light again establishes a contrast in effects where, as we shall 

 see, a similarity exists. Graber was prevented from cor- 

 rectly interpreting his results by attributing the movements 

 of animals to sensations instead of to physical causes. If 

 he had given up the anthropomorphic standpoint, he would 

 soon have discovered that his experiments show that the 

 more refrangible rays are more effective in causing the 

 orientation of an animal than the less refrangible ones. 



In none of the investigations of Bert, Lubbock, or Graber 

 has the influence of the direction of the rays on the orienta- 

 tion been studied. Graber, for example, took it for granted 

 that an animal moves to the light because, as he expressed 

 it, "it is fond of the light" or "the white." If it moves 

 in the opposite direction, it "is fond of the dark." Lubbock 

 remarks incidentally that "ants do not like light in their 

 nests, probably because they do not deem it safe." 



This sums up the opinions and results of the authors who 

 sought to explain anthropomorphically the phenomena which 

 interest us here. 



