SPECTRAL COLOR AND STIMULATION 475 



Later Loeb and Wasteneys ('15-'16) found the region of 

 maximum stimulating effect in a carbon-arc prismatic spectrum 

 to be in the yellow (560-578 mm), for Balanus larvae; in the blue 

 (460-480 mm) , for Eudendrium ; in the Blue near 495 mm for Aren- 

 icola larvae; in the blue (460-490 ijlij.), for Euglena viridis and in 

 the green about 535 /jlh for Chlamydomonas. These results are 

 in full harmony with those of earlier workers in so far as they 

 indicate that the relation between wave-length and stimulation 

 is not the same for all animals. Loeb, however, still holds that 

 it is the same for plants and animals, for he maintains that the 

 fact, that the maximum in Chlamydomonas is in the green, shows 

 that for plants it is not exclusively in the blue, just as has been 

 found to be true for animals. This fact was, however, fairly 

 well established before his first work appeared, as reference to 

 the following table (table 1) containing a summary of the re- 

 sults obtained in previous experiments will show. Other con- 

 clusions reached by Loeb and Wasteneys will be considered 

 later. 



The more important conclusions that a study of this table 

 warrants may be summarised as follows: 



1. A large proportion of the investigations were made with the 

 use of prismatic spectra, insuring fairly pure monochromatic 

 light, but in some gaslight was used as a source of illumination, 

 in others electric light and in still others sunhght. Moreover, in 

 some experiments the effects of the different colors on the process 

 of aggregations were studied, in others the effects on orientation 

 and in still others the effects on activity. The distribution of 

 energy in the different spectra used is however, similar in all 

 and in all cases in which two or more of the three reactions men- 

 tioned were studied on the same organisms, the results were 

 essentially the same, indicating that the relative stimulating 

 effect of the different wave-lengths is the same for all three sorts 

 of response. It is consequently possible to compare directly 

 the results obtained by most of the different investigators as 

 they are given in the table; but these results refer only to the 

 relative stimulating effect of rather large regions in the spectrum 

 and they are of such a nature that they show but little more than 



