1167 
that he did not yet attach to them the meaning which was after- 
wards given them by Arisz). [ have always used both terms in the 
sense in- which Arisz uses them, hence the apparent contradiction 
between the results of ArPáp Paár and my own. 
§ 2 Methods. 
The experiments were all carried out at the same temperature 
by placing the boxes with seedlings in an electrically heated thermo- 
stat, in’ which the temperature was kept constant by means of a 
thermoregulator. In the middle of the back wall of the thermostat 
there was an opening through which the axle of the clinostat passed, 
enclosed in an oil packing, so that no air could enter from outside ; 
this also secured the easy rotation of the axle. The end of the axle 
in the thermostat could be screwed into the clamp intended for 
holding the boxes with seedlings. The latter remained in the thermostat 
throughout the duration of the experiment and could in this way 
be stimulated geotropically as well as phototropically since the front 
and side walls were of glass, so that the plants could be rotated 
on the horizontal clinostat axis immediately after stimulation. All 
experiments were carried out with a single box of seedlings. The 
clamp was arranged for and held two boxes, but the second 
merely acted as a counterpoise in order to obtain as far as possible 
a uniform rotation of the clinostat. 
All experiments were carried out under a total pressure of one 
atmosphere and therefore the air in the thermostat was gradually 
replaced by nitrogen diffusing in from the commercial metal cylin- 
ders. Since the latter contain 4-—5 percent of oxygen, the gas was 
first passed through washing bottles containing alkaline pyrogallol, in 
order to remove the oxygen. Since, however, not all the oxygen 
was absorbed and CO was moreover formed, the gas was passed 
through a red-hot tube containing copper, in order to absorb the 
rest of the oxygen, and a little CuO, in order to oxidize the CO 
formed to CO, The gas treated in this manner was allowed to 
enter the thermostat and the air contained in the latter was thus 
gradually driven out through an exit. It took 14 to 2 hours to 
wash out all traces of oxygen, as was shown by estimations with 
a phosphorus pipette. 
In order to trace the influence of oxygen deprivation on the 
geotropie and phototropie stimulation processes I first carried out a 
1) W. H. Arisz. Untersuchungen über den Phototropismus. Recueil des Travaux 
Botaniques Néerlandais. Vol. All, 1915. 
