Dixon — A Transpiration Model. 



115 



osmotic solution within the membrane draws water from the 

 upper end of the tube, and, at the same time, distends the 

 membrane, while evaporation takes place from the upper side 

 of the cell into the space above. The membrane will be- 

 come and remain distended when the difference of vapour- 

 tension between the water at the top of the tube and in the 

 osmotic cell is greater than the difference between that of the 



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solution in the cell and of the space above the cell. For then the 

 amount of water evaporated will be less than the amount entering 

 into the cell, and the surplus will act in distending the walls. 

 Evaporation will continue to take place as long as the vapour- 

 tension of the solution is greater than that of the water-vapour in 

 the space above the upper side of the cell. 



I have since found that the conditions supposed in this 



