Geotropism and Phototropism in thc absence 

 of free oxygen 



by 



U. p. VAN AMEIJDEN. 



INTRODUCTION. 



The reason which led me to begin this investigation 

 was the fact that the problem of geotropism and photo- 

 tropism in the absence of free oxygen has so far been 

 very Uttle considered in connection with the more récent 

 investigations on gravitational and Hght stimuUs. In the 

 hterature Correns' view is still accepted who claims to 

 hâve shown, that seedHngs are able to exécute geotropic 

 curvatures in the présence of the minutest traces of 

 oxygen, whereas a higher oxygen-content the air is required 

 for phototropic movements. Considering the state of 

 knowledge at that time, we can understand how Correns 

 arrived at this conclusion. 



Later Àrpâd Paâl pubhshed a paper on this same sub- 

 ject. Àlthough he already took into account factors which 

 were still quite unknown at the time of Correns' 

 investigation, yet his conceptions with regard to the 

 problem in question, are not whoUy satisfactory. 



Thus there existed every reason for me to take up 

 this question up again and now on entirely différent lines. 

 In the first place I hâve taken care not to place experi- 



