122 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



transpiration co-operates in bringing about equal 

 pressure all over. 



Hartig and others also practically establish the 

 truth of the view that osmosis is the sole cause of 

 absorption and root-pressure, for the root's activity 

 is increased as the temperature of the soil rises 

 a fact irreconcilable with any notion of pressure 

 | at the roots being the cause. 



Hartig, as we have seen, ascribes osmotic activity to 

 all the parenchymatous and living cells, and claims 

 for the air-bubbles no other function but that of 

 moving the water from lumen to lumen : he also 

 accepts Theodore Hartig's experiment with the 

 vertical piece of branch, using it to prove how slight a 

 pressure is needed for movement. The water once 

 moved through the closing membrane of the pit, 

 becomes arranged by molecular forces in the new 

 cavity, rising in it by capillarity. 



But, Godlewski points out, the experiment with the 

 vertical stick has never been properly explained : 

 each writer in succession has assumed properties for it 

 which it does not possess, and the various proposed 

 explanations have again contradicted the principles 

 of physics. 



Suppose a glass tube, one meter long and filled 

 with water ; both ends closed by membrane perme- 



