1078 



BIOLOGICAL EFFECTS OF RADIATION 



the light of a monochromator for different exposure periods. For a stand- 

 ard of comparison the visible part of the spectrum of a Hefner lamp was 

 used. Minimum action was obtained at 0.86 X 10~^ gm. cal./cm.-/sec. 

 The energy was measured by a thermoelement. The results are sum- 

 marized in Table 1. 



Table 1. — Data Showing Phototropic Sensitivity Determined from the 

 Amount of Energy Required to Produce a Minimum Response in Oats 



{From Sonne, 40) 



It will be seen from this table that the amount of energy which just 

 causes phototropic curvature is very different for different wave-lengths. 

 The yellow (5700 A) is about 600 times as intense as is the white light 

 necessary to bring about the same response, while the green (5460 A) is 



o 



approximately 400 times as intense, and the blue (4360 A) only 0.03 as 

 strong as the energy of his standard white light. The blue is thus 

 approximately 10,000 times as effective phototropically as the green 

 and 20,000 times that of yellow. The violet (4050 A) is also very effective 

 but only about half that of the blue. 



Wiechulla (45) using the sporangiophores of Phycomyces found the 

 phototropic action of light passed through Schott color filters as com- 

 pared with that of white light to have the following values, in terms of tiie 

 time required to give the same bending: 



Orange 8000 



Yellow 180 



Yellow green 36 



Blue green 13.6 



Blue 4 



Bergann (3) made a very careful study of the effects of monochromatic 

 light on the growth and bending of Avena saliva as well as the effects 

 produced by a change of intensity and length of exposure. Employing 

 the method of placing the young plant between two opposite lights, he 

 concludes that the regions other than the red and infra-red produce 



