IV.] VARIOUS THEORIES, «lc. 8i 



to see that a slight pressure forced it into all the 

 cavities of the alburnum exposed by the section, and 

 even through the bordered pits, to a height of ten mm. 

 In this way he blocked up the hanina of the tracheides^ 

 and allowed the cacao-butter to congeal ; he then cut 

 a clean surface exposing the clean-cut walls of the 

 tracheides. A pressure of sixty cm. of mercury failed 

 to force water through, whence Elfving concluded that 

 apart from any possible molecular movements of 

 water imbibed in the cell-walls) the rapid currents 

 of water in the wood take place through the cavities 

 and not in the substance of the cell-walls. 



Elfving then goes on to discuss some other 

 phenomena, showing that water is held in the vessel 

 oi Aristoiochia, for instance, by exactly the same force 

 as it is held in a capillary tube of like calibre, and that 

 the tracheides and bordered pits are very impervious 

 to air. 



A piece of wood 3 cm. long allowed water to 

 pass easily under a pressure of i cm. of zuater^ 

 whereas the pressure of a column of niermry twenty 

 cm. high failed to drive air through. Now since one 

 cm. of water exerts a pressure roughly equal to t^-^-^ 

 atmosphere, we have to conclude that the shghtest 

 rise of pressure due to the expanding of an air bubble 

 in a tracheide, will drive water through. 



G 



