182 



Since the percentage of seediings which after 45 minutes 

 show a curvature of 3 m. m., is considerably higher than 

 after 40, or after 50 minutes, it follows that in this case 

 the reaction time is 45 minutes and the maximal cur- 

 vature 3 m. m. 



D. Photottopic experiments with Sinapis seediings. 



So far we hâve seen, that in Avena at a température 

 of 20° there is required for a geotropic curvature of 



2 m. m. a stimulus of 900 m. g. -secs, and for an equally 

 strong phototropic curvature a stimulus of 40 M.C.S., 

 further that in Sinapis at 23^ a geotropic reaction of 



3 m. m. is brought about by a stimulus of 600 m. g. -secs. 

 We might therefore expect that for a phototropic cur- 

 vature of 3 m. m. in Sinapis a stimulus of less than 40 

 M.C.S. would be required. I began therefore with a 

 quantity of light of 25 M.C.S. but even after two hours 

 I could not see the slightest reaction. Then I tried with 

 40, 60 M.C.S. but always with the same négative resuit. 

 Finally I stimulated with 400 M.C.S. and in that case 

 observed a distinct curvature after one hour. 



TABLE 10. 

 Strength of stimulus 400 M.C.S. 



Température 23° C. 



Time elapsed "o 

 since begin- 



ning of 

 stimulation 

 in minutes 



cn-C 



Extent of curvature in m. m. 



2 IV2 

 2 1 



2 l'I, 

 IV2 IV2 



IV2 172 



'/2 IV2 1 



1 



1 1 



1 



