CH. Ill] 



ROOT PRESSURE. 



75 



Phaseolus. An india-rubber tube T (Fig. 13) is tied on the 

 cut stump, S, of the plant and is filled with water : a capil- 

 lary glass tube G is tied into the tube, leaving about six 

 centimeters of rubber tube full of water between the 

 stump and the bottom of the glass tube. The glass tube 

 is now fixed in a clip and after a time drops of water fall 

 from the end E. To get an idea of the rate of flow it is 

 only necessary to gently pinch the rubber tube so as to 

 press the fluid out, and to absorb it with filter-paper held 



Fig. 13. Exp. 



at E.^ When the rubber tube is released and therefore 

 allowed to expand, a column of air is drawn into the tube 



1 The tube G, E, should be bent at right angles close to E, so that the 

 terminal centimeter points vertically downwards. 



