482 S. O. MAST 



which of these large regions is most effective. Concerning 

 relative efficiency all that can be ascertained is that all waves 

 longer than those in the region of maximum effect are less 

 efficient than those in this region, for they contain relatively 

 more energy. Regarding the efficiency of the shorter waves 

 which contain less energy than those in the region of maximum 

 effect no definite statement can be made. 



Only three of the investigators, Blaauw, Day and Gross, at- 

 tempted to ascertain the relative stimulating efficiency of the 

 different wave-lengths. Day and Gross used spectral colors 

 equal in energy but they tested only four different colors. 

 Blaauw tested more colors but I am not certain as to the 

 method used, having access only to an abstract of his paper. 



2. For seedfings of green plants, plumules and radicles, the 

 region in the spectrum of maximum stimulating effect is in the 

 blue or violet. For the fungi it is somewhat nearer the red. 

 For Bacterium photometricum it is in the infra-red and the 

 orange. For Oscillaria and Paramecium bursaria is it question- 

 able, activity and aggregation being probably determined by 

 chemical changes in the solution associated with the colors. 

 For Chlamydomonas it is in the green; for all other unicellular 

 forms tested it is in the blue, as it is also for the ccelenterates and 

 vermes and for a few of the molluscs and arthropods. But for 

 most of the molluscs and arthropods it appears to be in the 

 green or yellow. 



In none of the organisms mentioned in the table are the reac- 

 tions specifically associated with the wave-lengths; they are not 

 entirely independent of intensity. If, e.g., the green were made 

 relatively sufficiently intense, the region of maximum effect could 

 be changed from the blue to the green, etc. In the bees, how- 

 ever, and in many of the vertebrates, the evidence obtained indi- 

 cates that the reactions may be independent of the relative in- 

 tensity. Bees, e.g., can be trained to select any given color, 

 regardless of its intensity in relation to that of other colors ; and 

 such reactions to colors are the only ones which are like the 

 reactions associated with color- vision in man. 



