been warmed to the desired température, and it leaves the 

 vessel A through a tube, fixed to the narrow bottom-end. 



Réservoir B contains the water that is prepared in the 

 way, which will be discussed further on. Moreover the 

 réservoir B is connected with a COo-apparatus in order 

 that the outflowing water may be replaced by gaseous COo. 



The water in the réservoir B is kept at a température 

 of about 65° C the thermometer Tj indicating the tem- 

 pérature of this water. 



The rubber-stopper of the flask B is provided with a 

 siphon a, leading ofF the water and with a tube g, which 

 can be closed by a valve. It reaches to the bottom of 

 the flask and its use will be explained while discussing 

 the préparation of the water. Before flowing along the 

 Helodea-shoots the water passes through a glass-tube b 

 that has been bent several times. This tube is placed in 

 a waterbath Wo which is warmed at a lower température 

 than W] . The température of Wo is to be regulated by a 

 current of tapwater and if necessary, also by a gasburner. 

 In connection with the velocity of the watercurrent through 

 the tube b the température of Wo is chosen so that the 

 water reaches the Helodea-shoots at the desired tempéra- 

 ture. This température is controlled at the end of the 

 tube b by leading the water through a short, wide tube 

 M, containing a thermometer To. 



Hère it should be noted that this way of regulating 

 the température of the overflowing water has been chosen 

 to exclude saturation and over-saturation of this water 

 by COo. In the case of experiments at a high tempéra- 

 ture a casual saturation and over-saturation might cause 

 a development of gas-bubbles in the cylindrical vessel 

 A, the resuit of which might be a loss of -oxygen, the 

 bubbles carrying away this gas. This saturation and over- 

 saturation of the water, possible in the réservoir B, 

 will be prevented by cooling the water in the bath 



