Dixon — The Cohesion Theory of the Ascent of Sap. 61 



differences of vapour- and gas-pressure. These differences were 

 possibly quite local, not being able to equalise themselves, owing 

 to the resistance offered by the plaster of Paris to the passage of 

 water. 



Criticisms, based on the behaviour of an apparatus involving 

 the peculiar properties of plaster of Paris and on readings of 

 manometers so arranged, cannot be valid against any theory of 

 the elevation of water in the conducting tracts of plants. Nor 

 can we for one moment admit that "the behavior of this apparatus 

 was like that in trees as we know it," nor that " it is most prob- 

 able that the same fundamental physical principles are operative 

 in both cases." 



Botanical Laboratory, 

 Trinity College, Dublin, 

 Jan. 14th, 1903. 



SCIENT. PROC. R.D.S., VOL. X., PART I. Q 



