312 LIGHT AND THE BEHAVIOR OF ORGANISMS 



ultra-violet, the region of the spectrum which contains 

 least energy. 



Precisely how light produces chemical changes is un- 

 known, but it is clear that only those rays which are 

 absorbed can be effective. The efficiency is however not 

 proportional to the absorption. According to the excel- 

 lent researches of Luther and Forbes (1909), the reaction 

 between quinine and chromic acid is only affected by the 

 rays absorbed by the quinine, and not at all by those 

 absorbed by the chromic acid. Only about 4 per cent of 

 the light absorbed by the quinine is changed to chemical 

 energy. The ultra-violet and violet are most readily 

 absorbed, but the green is most efficient, i.e., a greater 

 amount of chemical action is caused by a given amount 

 of light energy absorbed in the green than by the same 

 amount absorbed in the violet and ultra-violet, showing 

 clearly that the efficiency is not proportional to the ab- 

 sorption. The same is true in case of photosynthesis, 

 which is supposed to be due to the action of light ab- 

 sorbed by the chlorophyll. Chlorophyll dissolved in alcohol 

 has, according to Reinke (1884), a prominent absorption 

 band in the red, a weak band in the orange, the yellow 

 and the green, while from 500/^^ on, i.e., in the blue and 

 violet, practically all light is absorbed. The maximum rate 

 of photosynthesis however takes place in the red, from 

 which it decreases rapidly in either direction, so that be- 

 yond the green in the region of maximum absorption there 

 is scarcely any photosynthesis. 



The specific effect of the different rays on chemical 

 reactions as well as on brightness sensation is evidently a 

 function of the length of the waves and the rate of vibra- 

 tion. The effect of the different rays is not proportional 

 to the energy in these rays, but the effect of light of a given 

 wave length is of course dependent upon the amplitude of 

 the waves, their intensity, as well as upon their length. 



