UNICELLULAR FORMS AND COLOR 329 



faintly transparent from 380 to 450''''. The blue was trans- 

 parent from 430 to 490^^ and from 690^'' out, and opaque 

 from 590 to 670''''. The green was transparent from 380 to 

 400"^, from 450 to 550'''' and from 680"'' out. It was 

 opaque between 580 and 660 ''^ and faintly transparent 

 between 400 and 450''''. 



Several amoebae were mounted under a large cover- 

 glass surrounded by a thin ring of vaseline so as to pre- 

 vent evaporation, and give ample space for free movement. 

 In this inclosure they were found to remain active and 

 in excellent condition for several days. The observations 

 were made on the stage of a compound microscope under 

 a magnification of about 150 diameters with very faint 

 illumination from the mirror. A beam of direct sunlight 

 which passed through 8 cm. of water was thrown on the 

 slide at an angle of about 45° with the stage. 



The organisms were exposed to light of different colors 

 by intercepting the beam with the colored filters. It was 

 found that amoebae which moved actively in weak diffuse 

 light ceased moving shortly after being suddenly exposed 

 to strong red light, but soon began again. If they were 

 now exposed to green the movement again ceased; the 

 same was true for blue after green and for direct sunlight 

 after blue. A change from direct sunlight to blue, blue 

 to green, or green to red, produced no apparent effect. 

 After being exposed to any color or any combination of 

 colors for a short time the movement was resumed. In 

 direct sunlight or in blue light it required longer than in 

 green or red. As a matter of fact, in these two colors, in 

 the red in particular, there was no cessation of movement 

 in some specimens, and only a slight decrease in others, 

 while in still others the movement stopped entirely. In 

 case of direct sunlight or blue, on the other hand, the 

 movement stopped abruptly in nearly every specimen 

 almost as soon as exposed. Similar but somewhat more 

 detailed results were obtained in the spectrum. 



b. Experiments with solar spectrum. — In these experi- 



