CHAPTER III. 

 Experiments in Air. 



The experiments described in this chapter, were per- 

 formed in order to obtain a measure of the déviations 

 which occur, if during a definite period the ordinary 

 atmosphère was replaced by nitrogen. Thèse experiments 

 are of four kinds: 



1. Geotropic experiments with seedhngs of Avena 

 sativa. 



2. Phototropic experiments with seedUngs of Avena 

 sativa. 



3. Geotropic experiments with seedhngs of Sinapis alba. 



4. Phototropic experiments with seedhngs of Sinapis 

 alba, 



In ail four cases the same method was foUowed in 

 principles. 



The boxes with the seedlings remained for half an hour 

 in the thermostat before stimulation. Two boxes of Avena 

 were always arranged together and fastened in the clamp 

 as described on p. 165. During the fore-period of half an 

 hour they were rotated on the axte of the clinostat. This 

 was of course also done after stimulation. In the experi- 

 ments with seedlings of Sinapis only one box at a time 

 was placed in the thermostat, because thèse, as stated 

 (p. 165) could not be rotated on the clinostat. 



À stimulus of definite strength was applied in each set 

 of experiments as follows: 



