178 



^=^ 



À comparison of tables 5 and 6 makes it quite évident, 

 on account of the high percentage of curvatures of 2 m. ni. 

 in table 6, that the reaction time at a strength of 40 

 M.C.S. is 75 minutes and that the maximal curvature 

 is 2 m.m. 



C. Geotropic experiments with Sinapis seedlings. 



Sinapis seedlings grown in the dark show a curve in 

 the hypocotyl, so that the upper part of this organ, with 

 the two cotylédons, is at right angles to the lower portion. 



The cotylédons do not spread 

 out (fig. 1). The germinated 

 seeds were always planted in 

 such a way that ail plants had 

 the bent portion pointing in 

 the same direction. In order to 

 render good measurements, the 

 curvature was always induced 

 in such a manner, that they 

 became opposed to the natural 

 curve of the hypocotyl. 



A striking feature of the 

 experiments was the large number of plants which did 

 not curve. I hâve therefore introduced into the tables a 

 new column, for the plants which did not curve, which 

 I hâve left out of account in my détermination of the 

 maximal reaction. A few preliminary experiments with a 

 strength of stimulus of 900 m. g. -secs, showed, that this 

 gave with Sinapis a much stronger curvature than with 

 Avena, so that I chose a duration of the stimulus of 10 

 minutes, which consequently corresponds to a strength 

 of stimulus of 600 m.g.-secs. As I did the experiments on 

 Sinapis in the summer months, it was impossible to keep 

 the température constant at 20° C, so that for ail thèse 

 experiments I chose a température 3 degrees higher. 



Fig. 1. 



