68 



BOOT PRESSURE. 



[CH. Ill 



at E. When the rubber tube- is released a column of 

 air is drawn into the tube and serves as an index of the 



Fig. H. Exp. 88. 



rate of flow as it travels up the tube, which should be 

 graduated. 



By watering the earth with warm water a greatly 

 accelerated rate of flow is obtained, but whether it is due 

 to increased root pressure or to the expansion of air in the 

 tissues is not easy to say. 



(89) Root pressure. 



To demonstrate the force of root pressure a striking 

 method is that used by Mr Gardiner in his lectures. He 

 uses a plant of Sparmannia growing in a large pot. The 



