392 



BOTANICAL GAZETTE 



[may 



ides and the rate of water movement through the membrane, 

 rhis emphasizes the caution that must be used in plasmolytic 

 xperiments on the rate of water movement through a membrane. 



is deals with solutions of different concentrations on 



Plasmoly 



membrane. The concentration of only one of 



>lysing solution , is known. In such 



the solutions, the plasmoly sing 

 experiments the internal concentration of the cells of plant or seed 

 is not known and is subject to change, that is, to variations in 

 pulling power. Results should not be referred to changes in the 

 permeability of the membrane alone until it has been found that 

 the internal concentration has remained constant during the 

 experiment (it is to be understood that this statement is intended 

 to apply to rate of water movement and not to the final equilibrium 

 attained by the two solutions). 



TABLE XV 



Rate of water movement as related to differences in con- 

 centration of solutions on opposite sides of membrane 



Osmotic pres- Osmotic pres- 

 sure OF EXTER- SURE OF INTER- 

 NAL SOLUTION NAL SOLUTION 



73-69 

 48.O. 



21.25 

 IO.3O 

 73-69 



73 69 



48.O. 

 21.25 



o 

 o 

 o 

 o 



10 



21 



IO 

 IO 



30 



30 

 30 



Effective 



OSMOTIC 



PRESSURE 



73- 

 48. 



69 







21. 



25 



10 



63 



30 

 39 



52 



42 



37 



.70 



10 



95 



Water (in mg.) passing 

 through membrane 



PER HOUR 



41.07 



37 65 



27.38 



13-59 

 21.39 



958 

 17. 11 



6.84 



Second 



37 65 



34.23 

 21.39 



17. 11 



20.54 

 11. 13 

 16.26 



8.56 



Comparison of permeability of membranes of different species 



Membranes from different species showed large differences in 

 permeability, as indicated by table XVI. Equal areas (19.635 



mm.) of membranes were measured 



sodium 



osmotic 



external 



will be seen that membranes 



species and different membranes of the same species show large 

 differences in permeability. The causes of these differences in the 



