124 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



periment is that the drop of water is absorbed to 

 replace the partial vacuum caused by the down flow 

 of the whole column, and the phenomenon is opposed 

 to and not in accordance with Hartig's and Boehm's 

 theories. The drop, as it sinks through the upper- 

 most membrane causes the concave meniscus in each 

 upper tracheide to become more raised and convex, 

 and therefore, for the moment, it cannot support so 

 much as before. 



All that the experiment really proves is that the 

 sum of the resistances to filtration of all the 

 membranes is smaller than the pressure of a column 

 of water as long as the wood used. 



After further criticisms, Godlewski decides that 

 every hypothesis which requires no further forces than 

 root-pressure, transpiration, and capillarity, must be 

 cast aside as insufficient ; for root-pressure may sink 

 to o when transpiration is active ; transpiration at 

 most cannot produce a vacuum, and hence cannot 

 lift beyond the pressure of one atmosphere ; and the 

 capillary machinery is not adapted to raise water more 

 than a few meters. 



Some other factor must be brought into requisition, 

 and Godlewski, like Westermaier, invokes the aid of 

 the living cells of the wood parenchyma and medul- 

 lary rays, which are never absent. These living cells, 



