430 STUDIES IN GENERAL PHYSIOLOGY 



few, are developed in the dark ; that darkness does not, how- 

 ever, interfere with the development of roots. 



2. It was of interest now to establish which rays of the 

 visible spectrum favor the development of polyps. The 

 effect of light on plants is known to be very strikingly a 

 function of the wave-length. Assimilation and in part the 

 formation of chlorophyll are pre-eminently functions of 

 the long wave-lengths. The heliotropic phenomena are 

 essentially a function of the blue rays. According to Sachs, 

 the ultra-violet rays are of special importance in the forma- 

 tion of blossoms in certain plants. I have shown that the 

 short light-waves are most effective heliotropically in animals 

 also. From this, however, no conclusions can be drawn as 

 to which rays influence most especially the formation of 

 polyps. I therefore studied this subject experimentally. 

 Unfortunately, these experiments were hampered because 

 no other means of obtaining monochromatic light were at 

 my disposal than the use of blue and red glass. I had 

 special boxes made for these experiments which were painted 

 black inside and one wall of which was formed by blue or 

 red glass. The dark-red glasses which I employed yielded a 

 light which was fairly monochromatic ; the dark-blue glasses 

 allowed some red to pass through. In the case of the light- 

 red and light-blue glasses the light was far from monochro- 

 matic. 



Experiment 1. On August 31 a large number of Euden- 

 drium were divided between two vessels, one of which was 

 placed in a box in dark-red light, the other in a box in dark- 

 blue light. As nearly as I could judge, the red and blue 

 glasses allowed about equal quantities of light to pass 

 through. The old polyps perished within three days, but 

 somewhat sooner in the red than in the blue light. On 

 September 4 I discovered the first new polyp in the blue 

 light, The number of new polyps in the blue light steadily 



