189 



If the percentage-flgures are compared with those of 

 table 3, the agreement is very striking, for both tables 

 show a maximal curvature of 2 m. m. When there is a 

 fore-period of 5 hours in nitrogen a great weakening of 

 the reaction is traceable, whilst there is absolutely no 

 reaction when the fore-period in nitrogen amounts to 6 

 hours. (PI. XVIII, fig, 1). 



B. Phototropic expedments with Avena. 



Everything that has been said of the course of the 

 geotropic experiments, applies also mutatis mutandis to 

 thèse, with the différence naturally, that the stimulus used 

 was 40 M.C.S. and that the extent of curvature was 

 measured after 75 minutes. Hère also the curvature-process 

 was followed out for a longer time, but no increase in 

 the reaction was ever observed. 



TABLE 15. 



Strength of stimulus 40 M.C.S. Température 20° C. 



Reaction-time 75 minutes. 



