310 LIGHT AND THE BEHAVIOR OF ORGANISMS 



In the last two equations it is clearly shown that the 

 longer waves as well as the shorter are actinic. Stobbe 

 investigated the reactions of numerous so-called fulgides in 

 the different rays of the spectrum C'Steinheilschen Spectro- 

 graphen") and found seventeen which behave much like 

 triphenylfulgid. There is however considerable varia- 

 tion as to the specific effect of the rays in the different 

 forms. In general the shorter waves cause the fulgides to 

 become darker in color, while the longer ones cause them 

 to become lighter. But in some it is the violet which pro- 

 duces the dark shades, while in others it is the ultra-violet 

 or the blue. " Je mehr sich die Farbe eines Fulgides ver- 

 tieft, je w^eiter sich die Absorption eines Fulgides nach 

 dem rothen Ende des Spectrums erstreckt, um so weiter 

 riickt auch die Erregungszone nach derselben Richtung 

 vor" (1908, p. 31). 



In white light the fulgides turn dark, just as in mono- 

 chromatic light, but strange as it may appear the reac- 

 tion is much less pronounced, even if the white light has 

 more of the effective rays than the monochromatic light of 

 any given region in the spectum. The relatively feeble 

 effect of white light must be due to the presence of the 

 longer waves, which, as represented in the equation above, 

 tend to produce the lighter shades and consequently retard 

 the production of the darker. It may be well to call 

 attention to the fact in passing that the investigations of 

 Lubbock on Daphnia, of Wilson on Hydra and of Wiesner 

 on some of the higher plants show that as in the ful- 

 gides, monochromatic light consisting of certain rays is 

 more effective in causing reactions than the same light in 

 combination with other rays. 



It is evident from the last two equations that the longer 

 rays as well as the shorter may have a specific photo- 

 chemical effect. Triphenylfulgid, e.g., is changed from dark 

 brown to orange yellow by the longer waves and not by 

 the shorter. There are many other reactions which are 

 induced only by the longer waves. Among the most 



