195 



If this table is compared with the results obtained after 

 a fore-period in oxygen of 6 hours, which are collected 

 in table 13, then the différence can only be explained by 

 the fact that in the earlier expérimenta the stimulus was 

 given in the absence of and in the later ones in the 

 présence of oxygen. We hâve now therefore become 

 entitled to the conclusion that the seedlings can no longer 

 perceive a geotropic stimulus when they hâve been for 

 a long time deprived of oxygen. 



We should note, however, that the curvature of table 

 18 are smaller than those wich arise under normal con- 

 ditions. This suggests, that, as a resuit of continued want 

 of oxygen, the seedlings undergo a harmful influence, 

 which is still felt when normal conditions are re-estabUshed. 



F. Phototropic experiments with Avena. 



Fore-period of 8 hours in nitrogen. Àfterwards photo- 

 tropic stimulation in air. (PI. XVIII, fig. 4), 



TABLE 19. 

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

 Reaction-time 75 minutes. 



The resuit is exactly the same as in the geotropic 

 experiments and it follows in the same way that the 



