THE INFLUENCE OF LIGHT ON ORGANS 427 



time 386 pounds in weight, From this observation Pleasan- 

 ton concluded that violet light is favorable to the growth of 

 pigs. General Pleasanton's book is printed in blue type, and 

 gives an explanation of all natural phenomena, from love 

 down to the activity of a volcano. 



Emil Young made a series of experiments on the influ- 

 ence of colored light on development. He concluded that 

 violet light hastens to a certain degree the development of 

 frogs' eggs, and the growth of embryos, while green light is 

 fatal to or greatly retards development. Young's results are 

 incomprehensible. The larvae of frogs develop naturally in 

 daylight, and the latter contains more green light than light 

 which has passed through a green screen, and should accord- 

 ing to Young be fatal. We might, perhaps, assume that 

 some other light counteracts the effect of the green light 

 sufficiently to do away with this fatal effect. From Young's 

 experiments, however, this does not seem to be the case. It 

 is quite possible that other conditions (such as the develop- 

 ment of micro-organisms) affected the results of Young's 

 experiments, which lasted through several weeks. 



Driesch used monochromatic light and carried out the 

 same experiments as Young on freshly fertilized eggs of 

 Rana, Echinus, and Planorbis, and found, in all cases, that 

 light "has no influence on the segmentation or the forma- 

 tion of organs; under otherwise similar conditions these 

 phenomena occur with the same velocity in darkness, in 

 white, in green, in violet, or in other lights." 



In my experiments on heteromorphosis in Naples, I 

 observed that the polyps of Eudendrium racemosum are 

 positively heliotropic, and that the number of polyps which 

 develop is apparently dependent on the intensity of the light. 

 It seemed that fewer polyps were developed in weak light 

 than in strong light. This accidental observation led me to 

 study the influence of light on the development of organs 



