IV.] VARIOUS THEORIES, &c. 113 



owing to the impermeability of the wet mem- 

 branes for air, and the enormous friction of the 

 air-bubbles. 



A paper of some interest at the time was published 

 by Max Scheit 1 early in 1884, in which the author 

 boldly denied that air-bubbles exist in the vessels, &c. 

 during the life of the plant, and surmises that they 

 have entered the sections, &c. at the moment of 

 cutting. He argues that only two modes of entrance 

 are possible for the air (i) through the stomata, 

 which do not communicate with vessels, and (2) as air 

 dissolved in the water entering at the roots. Von 

 Hohnel and Wiesner had proved that air cannot pass 

 directly into vessels, and we know it will not readily 

 traverse wet membranes and since water is always 

 to be found in the vessels, &c., their walls are never 

 dry during life. 



Scheit argued that any air dissolved in water at the 

 roots would be used before it reached the places where 

 it is said to separate out. He gives some conclusive 

 proofs of the impermeability to air of wet wood : 

 even 80 to 120 cm. of mercury failed to drive air 

 through 2 3 cm. of wood. 



He concluded that only water and aqueous vapour 



1 "Die Wasserbewegung im Holze." Bot. Zeitung, March, 1884, 

 p. 177. 



I 



