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The dimensions of the thermostat were chosen as small 

 as possible in order to expedite the replacement of 

 the air in the inner box by nitrogen. In the centre of 

 the back walls there was an opening through which the 

 axte (PI. XVI, a) of the clinostat passed, contained in an 

 oil-packing (PI. XVI, b) so that the wall was completely 

 air-tight and the axte could turn without appréciable 

 friction. To the end of the clinostat-axte in th'e thermostat 

 a clamp (Pi. XV and XVI, c) could be screwed for the 

 purpose of attacking the vessels containing the seedlings. 

 Since it was necessary before measuring the curvatures 

 to take the seedlings out of the thermostat, it was 

 désirable so to construct the fastening that this could be 

 done as quickly as possible. For this reason a screw 

 (PI. XV and XVL d) was attacked to each top corner 

 of the inner box, in such a way that the lid, provided 

 on the under side with ad indiarubber plate, could still 

 just be placed free on the inner-box. Two springs (PI. XV, e) 

 were now placed through the screws, and pressed the lid 

 on the box so as to make it air-tight, after a nut (PI. XV 

 and XVI, f) had been screwed down on each of the 

 screws. In the space between the inner and outer box, 

 two heating-lamps (PI. XV and XVI, g) were placed, and 

 in addition, a mercury thermoregulator {h) and two stirring- 

 arrangements (i), which were driven by an electric-motor, 

 and finally, there was a thermometer. For the rest, this 

 space was completely filled with water. In order to open 

 the thermostat, each time enough water was syphoned 

 out to make the level descend just below the hd. Through 

 the lid two tubes passed, of which one (k) was bent at 

 a right-angle just under the lid, and ended blindly, but 

 was provided with many small holes. This sewed for the 

 admission of nitrogen. The other tube (/) reached almost 

 to the bottom of the inner-box, and served as exit of 

 nitrogen. 



