NO. 1 1 



IMIOTOTROl'IC SENSITIVITY JOHNSTON 



13 



The efficiency value for line 4358 A falls below the curve. This is to 

 be expected if the points on the curve adjacent to wave length 4358 A 

 contained scattered light of more phototropic effectiveness. The value 

 for the 4047 A line is above the curve. It may be noted that this 

 radiation was not exactly monochromatic, since an examination with 

 the spectroscope showed very faintly the presence of lines 4078 A 



•4000 -4100 4200 4300 4400 



46O0 4TO0 4600 4900 SOOO 5IOO 5200 530O 



Fig. 4. — Phototropic sensitivity curve. The ordinates are relative sensitivity 

 values, the abscissae, wave lengths in angstroms, and the horizontal bars indicate 

 the wave-length ranges of the balance points. Circles indicate points obtained 

 with niters combined with the monochromator. The crosses show where mercury 

 lines were used. 



and 4358 A. This would make the apparent eiTectiveness of this line 

 (4047 A) greater than its actual elTectiveness and hence raise it above 

 the curve. On the other hand, the curve itself is doubtless a little 

 higher than that which would have been obtained had it been possible 

 to use filters in addition to the monochromator for this region. It 

 may be possible that the phototropic sensitivity curve actually begins 

 to rise at this point, although there is no indication of this from the 

 other data obtained in this work. It is to be expected that in the 

 ultraviolet region the curve would rise, owing to injury of cells on the 

 proximal side of the seedling. 



