432 STUDIES IN GENERAL PHYSIOLOGY 



This time I also made the reverse experiment. The 

 polyps formed in blue light were exposed to red light (the 

 blue glass was replaced by a red one on September 6). After 

 five days all the newly developed polyps had perished. By 

 September 13 only a few diminutive polyps had developed. 



Experiment 3. On August 25 eight stems of Euden- 

 drium culture were placed behind light-red glass (which 

 allowed also some blue light to pass through), and nine 

 stems of the same culture behind blue glass which was not 

 very dark. On August 30 a number of polyps had devel- 

 oped, not only behind the light-blue, but also behind the 

 light-red glass. The light-red screen was then replaced by 

 a dark-red one; while the number of polyps constantly 

 increased in the blue light, development soon ceased behind 

 the dark-red screen. On September 1 the eight stems in the 

 red light had only sixteen small polyps, while the nine in the 

 blue light, which were of the same size and from the same 

 culture, had eighty polyps. On the following day eighteen 

 polyps had developed in the red light, while the stems in the 

 blue light were literally covered with them. 



On September 5 the glasses were exchanged ; the animals 

 which up to this time had been behind the red screen were 

 now exposed to blue light, while those which had been 

 exposed to blue light were placed behind the dark-red screen. 

 The number of polyps on the stems in the blue light (which 

 had formerly been in the red) increased rapidly ; on Septem- 

 ber 9 the number had grown to 27, on the 10th to 40, and 

 so on. The polyps on the animals in the red light (which 

 had formerly been in the blue) not only did not increase in 

 number, but they began to die, and on the llth only a few 

 were left which looked sickly. 



A fourth experiment corroborated the result that numerous 

 and vigorous polyps are formed behind a dark-blue screen, 

 while in red light only roots are formed. 



