SPECTRAL COLOR AND STIMULATION 525 



2. In all of the species studied stimulation by light was found 

 to depend upon the wave-length, i.e., certain spectral colors are 

 much more efficient as stimulating agents than others. In the 

 spectrum from the region of the maximum the stimulating effi- 

 ciency decreases rather rapidly in either direction and the effec- 

 tive region is much shorter than the visible spectrum. 



3. There is no evidence indicating that stimulation in any of 

 the species studied is independent of luminous intensity, for if 

 the light in the spectrum on either side of the maximum be made 

 sufficiently intense it becomes more effective than that at the 

 maximum. This holds also for the reaction of plants to light 

 and probably for all photochemical reactions. There is conse- 

 quently no evidence indicating the presence of color-vision in 

 any of the forms studied. Bees are the lowest form in which 

 color-vision has been clearly established. 



4. The distribution in the spectrum of stimulating efficiency 

 differs in some species that are closely related (Gonium and Pan- 

 dorina) and is essentially the same in some that are not closely 

 related (Euglena and Lumbricus). The region of maximum, 

 efficiency is near 483 ^/x for Euglena, Trachelomonas, Phacus, 

 Gonium, Arenicola, and Lumbricus; near 524 nij, for Pando- 

 rina, Eudorina and Spondylomorum ; near 503 ^u^ for Chlamy- 

 domonas and blowfly larvae; near 465 mm for green plants and 

 somewhat nearer the red for fungi. 



5. It consequently differs for plants as well as for animals, 

 but the shorter wave-lengths are relatively more efficient for 

 green plants than they are for any animals and there is nothing 

 in the nature of color-vision in any of the plants. The conten- 

 tion therefore that the reactions to colors in plants and animals 

 is the same is not well founded, although some of the chromatic 

 reactions in animals may be essentially the same as those in 

 plants. 



6. The distribution in the spectrum of stimulating efficiency 

 in any given species is continuously the same, regardless of changes 

 in physiological states, environment and character of response, 

 e.g., it is the same in individuals when they are negative as it is 

 when they are positive. 



