66 Henry H. Dixon. 



which, SO far as the writer can understand, does not differ essentially 

 from that advocated by Quincke andBöhm. Underlying Askenasy's 

 account is the same fallacy which invalidates these authors' views,, 

 viz. that the tension can be transmitted in the water between 

 bubbles of considerable size and the walls. He appealed^) to hypo- 

 thetical adhesive properties of the imbibed walls to explain how a 

 layer of water might be held between the bubbles and the walls, 

 and he assumed that the tension would be transmitted in this layer. 

 It is evident, however, that no advantage can be obtained by in- 

 creasing the range of the adhesive forces between the water and 

 the walls. In view of the mobility of water such a hypothetical 

 attraction between the comparatively far removed water particles 

 and the walls would increase the tendency of the films round the 

 bubbles to thin out, and all the more preclude the transmission of 

 tension between the bubble and the wall of the containing trachea. 

 Askenasy exporimentally produced tension in water by evaporation 

 from porous clay, in the same way as B ö h m did, by the evaporation 

 from the leaves of a plant. He assigned a similar rôle to the surface 

 tension forces in the cell- walls of the evaporating cells as was assigned 

 by the authors of the theory of the Tensile Transpiration Current. 



^) E. Askenasy, Ueber das Saftsteigen. Loc. cit., p. 19. 



