210 



This fore-period of the material in a given atmosphère, 

 plays therefore an important rôle in determining whether 

 perception is still possible in this atmosphère or not. 

 Without further data no limits of oxygen-withdrawal can 

 be fixed at which perception still is, and is no longer 

 possible. 



Adopting the method of exhausting in a short time 

 one can easely investigate the influence of oxygen with- 

 drawal on perception and reaction separately; in the first 

 case by applying the stimulus in and vacuum and allowing 

 the reaction to take place in ordinary air, in the other 

 case, by stimulating in air and letting the reaction take 

 place in a vacuum. Although I found it impossible to 

 carry out this method of investigation, because in my 

 experiments it took IV2 to 2 hours for the air in the 

 thermostat to be replaced by nitrogen, I nevertheless 

 consider I hâve determined separately the influence of 

 oxygen-withdrawal on the perception and on the reaction. 



Closely connected with this investigation are the papers 

 dealing with the influence of withdrawal of oxygen on 

 growth ^), because the geotropic and phototropic stimu- 

 lation movements are both growth-movements. Now the 

 opinions as to how growth in seedlings is influenced by 

 an oxygen-free environment are greatly at variance with 

 each other. Wortmann, Correns, Wieler and Shull 

 State that without the least trace of oxygen no growth 



M Wortmann. l.c, p. 509. 



Correns. l.c, p. 139. 



Wieler, Le. p. 189. 



A. ]. Nabokich. Ueber die Wachstumsreize. Beih. z. Bot. Centralbl. 

 XXVI, 1. 1910, p. 7. 



E. Lehmann. Zur Kenntnis des anaeroben Wachstums hôhercr 

 Pflanzen. Jahrb. f. wiss. Botanik. Bd. 42, 1911. p. 61. 



Ch. A. Shull. The oxygen minimum and the germination of Xan- 

 thium seeds. The Botanical Gazette LU, 1911, pag. 453. 



