SPECTRAL COLOR AND STIMULATION 473 



Some of these investigators maintained that all classes of 

 vertebrates, some of the arthropods and even some of the 

 worms have color-vision. They used the so-called preference 

 method in their investigations on the response of animals to 

 colors, and largely owing to this and to the fact that they 

 proceeded from a psychological point of view, their work has 

 been severely criticised. However, a number of them, Lubbock 

 in particular, used monochromatic light of high purity, and made 

 a very thorough objective investigation of the subject; and more- 

 over, a large proportion of their results has been abundantly 

 confirmed. But many of their conclusions, especially those con- 

 cerning subjective sensations have not been generally accepted. 



Botanists have been interested in the response to colors very 

 largely from a purely physiological point of view, and a num- 

 ber of them have made very extensive and thorough studies of 

 the subject, using spectra of high purity, e.g., Guillemin ('58), 

 Wiesner ('79), Strasburger ('78), and Blaauw ('09). In gen- 

 eral it has been found that the region of maximum stimulation 

 for green plants is in the blue, although some hold that it is 

 in the violet; and that for fungi it is somewhat nearer the red 

 end of the spectrum than it is for green plants. The most 

 extreme shift in this direction that is known was discovered by 

 Engelmann ('82) in his work on Bacterium photometricum in 

 which he found a primary and a secondary maximum, the former 

 in the infra-red and the latter in the orange. 



A number of investigators have also been interested in the 

 study of responses of animals to colors largely from the point of 

 view mentioned above. Prominent among these may be men- 

 tioned Engelmann ('82), Verworn ('89), Hess ('10) and others. 



Loeb should probably also be included in this group. His 

 aim was, however, quite different from that of the other inves- 

 tigators mentioned. He was not interested in the evolution of 

 consciousness, and he objected strenuously to the conclusion that 

 psychic phenomena are involved in the reactions of animals. 

 In support of this objection he attempted to prove that the 

 reactions in plants and animals are fundamentally identical, 

 maintaining that such a proof would show that there are no 



