THE HETEROSTATIC METHOD 



189 



feeble it may be. The very great advantage of the auxiliary 

 stimulator is that under its action the sensitiveness of the 

 specimen remains constant for even very long periods. 

 This will be seen from the account of the following experi- 

 ment. The auxiliary stimulator was so adjusted that the 

 specimen was on the verge of response ; different rays of the 

 spectrum were now thrown on the plant by means of the 

 reflecting mirror m. Under red light (B, 680 XX) the relative 

 activity was 100 ; under blue light (486 XX) the activity 

 declined to 56 : hence the blue rays are less effective than the 



Fig. 50. Heterostatic Method for rendering ineffective 

 Stimulus effective 



Light from Pointolite k falls on the plant, and adjustment is made 

 for inducing verge of stimulation. Rays from different 

 regions of the spectrum are thrown on the plant by the reflect- 

 ing mirror m, the stand being provided with a tangent screw. 



red in the proportion of 56 : 100. The red was applied for a 

 second time, and the activity was now found to be the same 

 as before, namely 100. The activity under orange light 

 (656 XX) was 66 ; blue light was applied for a second time, 

 and the activity was found to be the same as before, namely 

 56. Carrying the observations backwards and forwards 

 gave similar results, showing the remarkable uniformity 

 secured by the method of auxiliary stimulation. 



Additive effect of light. — In order to prove that the effect 

 of incident radiation is added to that of the auxiliary light 

 I carried out the following experiments. The auxiliary 



