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between the beginning of stimulation and the point at 

 which the curvature flrst becomes visible. Since I hâve 

 found that when the reaction takes place in the absence 

 of oxygen, whilst the stimulus is normally perceived, a 

 weaker curvature arises, it foUows directly that the first 

 beginning of the curvature takes place later. And this 

 is, what Arpâd Paâl regards as a lengthening of the 

 reaction-time. In this respect also therefore my results are 

 not in conflict with his. 



In most investigations, in which the influence of oxygen- 

 withdrawal was always determined by pumping out the 

 air, it is mentioned that the plants in a definite oxygen- 

 content are still able to exécute a geotropic or phototropic 

 stimulation-process. When, however, still more oxygen is 

 withdrawn, they lose this power. I cannot accept this 

 opinion and the cause must, I think, be sought for 

 exclusively in the method by which ail thèse investigations 

 were carried out, namely in the partial or total vacuum, 

 in which the expérimental material was placed. My 

 experiments, following an entirely différent method, also 

 led to an entirely différent resuit. In the fîrst place my 

 seedlings during the experiments were always under a 

 pressure of one atmosphère, so that any possible influence 

 of a vacuum was whoUy excluded. The material which 

 was kept in an atmosphère completely free from oxygen, 

 preserved in it for some time the power to perceive a 

 stimulus of 900 m. g. -secs, or of 40 M.C.S., which power, 

 however, was entirely lost after some hours. 



In the gas-mixtures with low oxygen-content, which I 

 investigated, stimuli of this strength were still normally 

 perceived, even when the seedlings had been for 10 hours 

 in this atmosphère after the application of the stimulus. 

 Yet this amount of oxygen was found to be insufïicient 

 for the seedlings in the long run, at least perception was 

 considerably weakened after a fore-period of 24 hours. 



