194 



Thèse experiments therefore ail hâve the same resuit. 

 We find that when the seedlings hâve been deprived of 

 oxygen for a sufRciently long time, a stimulus applied in 

 nitrogen cannot find expression, although immediately after 

 stimulation, the nitrogen was replaced by atmospheric air. 



May we then at once conclude, that the stimulus is 

 not perceived? I imagine not, for it is always quite possible 

 that in ail the cases described above, the stimulus was 

 really perceived, but that the processes in the plant which 

 cause the reaction had already been afîected in advance 

 by the prolonged absence of oxygen to such an extent 

 that no curvatures took place. In order to settle this point, 

 I did experiments in which the seedlings were given as 

 long a fore-period in nitrogen, as in those cases described 

 above in which a reaction no longer occured, but now 

 the stimulus was not applied until the nitrogen had been 

 replaced by air, so that therefore stimulation took place 

 in air. The passing through of air was of course continued 

 during the reaction-time. 



E. Geotropic experiments with Avena. 



A fore-period of 6 hours in nitrogen. Afterwards for 

 V4 hour geotropic stimulation in air. (PI. XVIII, fig. 3). 



TABLE 18. 



Strength of stimulus 900 m. g. -secs. Température 20^ C. 



Reaction-time 65 minutes. 



