402 CHAP. XXXV. TORSION UNDER DIFFUSE STIMULATION 



and the rate was 24 at the twenty-fifth minute. The re- 

 sults are given in detail in the following tabular statements : 



Table L. — Effect of Diffuse 

 Sunlight on Porana. 



Table LI. — Effect of Diffuse 

 Sunlight on Thunbergia. 



The results given above show that the effect of the 

 stimulus of light is the same as that of other modes of 

 stimulation. The effect of minimal stimulation is seen in 

 the preliminary enhancement of the rate of torsion, while 

 maximal stimulation caused a retardation of the rate. 

 When exposure to light is continued for a longer period, 

 the retardation culminates in actual reversal. 



Effect of red and of blue light. — In my investigation of 

 growth under the action of light of different colours, I found 

 that blue light was very effective in the retardation of 

 growth. Red light induced practically no retardation 

 (p. 78). I could not be quite certain if it did not induce 

 the opposite effect of enhancement. 



The contrasted effects of red and of blue light on 

 autonomous torsion are, however, very marked. The 

 different lights were obtained by means of colour-filters 

 placed in the path of strong white light. 



Experiment 222. — The normal rate of torsion in Thun- 

 bergia was 14 ; this was enhanced to 38 under continuous 

 exposure to diffuse red light. On the cessation of light 

 there was a complete recovery to the normal rate of 14 

 in the course of 15 minutes. The same specimen was next 

 subjected to the action of blue light. The retardation was 



