211 



can take place, Nabokich and Lehmann on the 

 other hand hold the opinion that this is quite possible, 

 Lehmann says, for example, that seedlings of He/zanf/ius 

 continued to grow for 24 hours and longer without 

 oxygen. Àfterwards they gradually stopped and when 

 air was introduced, became again normal. Nevertheless 

 he asserts explicitly that ail plants are not capable of 

 growth without oxygen. 



Thèse investigations are therefore partly in agreement 

 with my results. Even although it were to be shown that 

 no growth can take place in an atmosphère completely 

 free from oxygen, my results would not necessarily be 

 in contradiction therewith, because it might quite well 

 be possible that the seedlings which had lost their power 

 of growth through deprivation of oxygen, had again 

 recovered it in conséquence of a geotropic or phototropic 

 stimulus. 



Summary. 



Ail experiments were carried out with a stimulus of 

 definite, known intensity. 



In order to détermine the influence of oxygen with- 

 drawal, no complète or partial vacuum was used, but the 

 air was always replaced by nitrogen by means of graduai 

 diffusion. Thus the seedlings always remained under a 

 pressure of one atmosphère. 



When seedlings, which hâve been long enough removed 

 from the influence of oxygen, are stimulated geotropically 

 or phototropically, likewise in the absence of oxygen and 

 are then at once placed in atmospheric air, they are 

 unable to exécute a reaction. 



If the seedlings are given a similar fore-period in an 

 oxygen-free atmosphère, but if the stimulus is administered 

 in air, in which the plants are also left subsequently, a 

 reaction does occur. 



