Grafts et al. 



114 



Water in Plants 



This discrepancy was attributed to various causes: 1) adhesion of the 

 protoplast to the wall ; 2) the slight difference in osmotic pressure between 

 a solution effecting limiting plasmolysis and that causing incipient plas- 

 molysis; 3) time of treatment, insufficient or excessive; 4) failure to ac- 

 count for the volume change between the normal and incipiently plasmolyzed 

 states; 5) excessive proportion of protoplasm in the cells; 6) inelastic 

 stretching of cell walls. 



/atmospheres 

 IS 6 10 



Fig. 36. — Osmotic pressure values of leaf cells of Bergenia cordifolia. Solid lines 

 represent initial plasmolysis, dashed lines d'eplasmolysis, and dotted lines cryoscopic 

 values on the expressed sap. (Buhmann, 1935). 



The sampling error involved in making plasmolytic tests usually one 

 day after the cryoscopic tests, and using different leaves for each, may 

 have influenced these results. Epidermis was chosen for many of the 

 plasmolytic determinations; these were compared with cryoscopic values 

 obtained on sap expressed from many whole leaves. Oppenheimer's 



