314 LIGHT AND THE BEHAVIOR OF ORGANISMS 



organisms which are not very sensitive it is, however, un- 

 hkely that a few stray foreign rays mixed with a given 

 color will alter the reactions. In reviewing the work on 

 reactions in colored light and formulating conclusions it 

 will consequently be necessary to consider carefully the 

 methods used in such work. 



Poggioli (1817) was the first to study the relative effect 

 of light waves of different lengths on the reactions of 

 plants. He exposed seedlings of Brassica and Raphanus in 

 different parts of the spectrum and found that they turn 

 toward the source of light in the red as well as in the 

 violet, but that the reaction in the latter occurs much 

 more rapidly than in the former. He does not mention 

 the reaction in other parts of the spectrum. These 

 results seem to have remained unchallenged for twenty- 

 five years, when Payer (1842), after studying the reac- 

 tions of different seedlings in a solar prismatic spectrum 

 and behind different color media, came to the conclusion 

 that red, orange, yellow and green act like darkness, and 

 that blue is more active than violet. This conclusion, 

 however, although supported by Sachs, is not in harmony 

 with the experimental results of Gardner, Dutrochet and 

 Pouillet, Guillemin, Wiesner and others. Gardner (1844) 

 found that all the seedlings in a trough which extended 

 beyond the solar prismatic spectrum into the ultra-violet 

 and the infra-red bent toward the sources of light, but that 

 they deflected slightly toward the indigo. The deflection 

 toward the indigo was no doubt due to light reflected by 

 the seedlings in this region of the spectrum. Dutrochet 

 and Pouillet (1844) obtained similar results in their experi- 

 ments with the roots of white and black mustard in a 

 strong solar prismatic spectrum. They concluded that 

 all the rays, including ultra-violet and infra-red, cause the 

 roots to bend from the source of the light, but that the 

 blue is most active. 



Guillemin (1858) made a more detailed study of this 

 subject than had previously been made. His methods 



