SUCTIONAL RESPONSE AND ASCENT OF SAP 



365 



the specimen is mounted by means of a water-tight india- 

 rubber cork. The vessel is closed at the bottom also by 

 means of a large cork through which enter four tubes. One 

 of these, controlled by the stop-cock A, is connected with 

 the capillary potometer-tube. The second, controlled by A', 

 leads to the compensating vessel C, filled with water. The 

 interior ends of these two tubes reach almost to the top 

 of the plant-vessel. The third, with stop-cock P,', leads to 



Fig. 156. Diagrammatic Representation of the Shoshungraph 



plant-vessel ; c, compensator ; r, reservoir. The potometer-tube is 

 controlled by stop-cock, A ; compensator by a' ; and reservoir by b'. 

 b is the stop-cock of the outflow pipe ; d, recording drum driven by 

 clockwork ; p, collar carrying recording pen, seen magnified above. 

 The water-index is followed by appropriate manipulation of the 

 wheel, w. 



the reservoir R, from which water at various temperatures 

 or different chemical reagents may be introduced. The 

 fourth is an outlet-tube controlled by the stop-cock B. 



Adjustment for Unbalanced Record. — The great 

 difficulty in connection with delicate experiments arises from 

 the presence of air-bubbles in the plant-vessel, which are not 

 easy to expel. This is done, however, by means of an escape- 

 tube, with a stop-cock, which runs through the upper cork, 



