Chapter VIII 



143 



Active Relations 



negatively charged; the movable liquid carries plus (H+) ions. The mem- 

 brane potential (E) across this pore is greater than that (e) across the 

 larger pore setting up a driving force that produces a movement of the 

 positively charged liquid toward the left. Since the normal flow is also in 

 this direction, the residual flow is termed positive anomalous osmosis. 



The membrane in B is positively charged. The smaller pore prefer- 

 entially transports anions, therefore exhibits a smaller positive potential 

 (e) than the larger (E). Movement of the vein of liquid in this pore is 

 toward the more dilute solution, and is termed negative anomalous osmosis. 



Vacuole \ Cytoplasm 



JugariiA— Sugar 



t 



Malic Ik Malic 

 acid I ^ acid 



£yternally 

 supplied 

 matate 



B 



+ + 

 + + 

 + + 

 + + 



4^ 



f\ 



+ + 



+ + 



Fig. 42. — Electroosmotic flow according to Bennet-Clark and Bexon (1943). 



Bennet-Clark and Bexon (1943) have introduced a theory of water 

 movement by which they attempt to explain secretion across the tonoplast 

 into the vacuole due to electrokinetic activity. Instead of the classical model 



solution I semipermeable membrane | water, 

 they prefer 



solution I permeable membrane | water 



as being more characteristic of the cell. They propose that the excess 

 turgor observed in their earlier work (Bennet-Clark, et al., 1936) is due 

 to continuous diffusion of solute. This might account for a potential differ- 

 ence across the tonoplast and provide the driving force for electroosmosis. 

 Or the water might move as water of hydration with the solute, a process 

 similar to Osterhout and Murray's anaphoresis. Turgor in cells is pic- 

 tured as resulting from such a continuous diffusion process rather than 

 from a "static osmotic equilibrium which could only be attained with an 



