384 SCIENCE PROGRESS 



pressure. Then if Fp is the volume of the plasmolysed proto- 

 plast and vacuole, V, the original internal volume of the cell, 

 C the osmotic concentration of the plasmolysing solution, the 

 original osmotic concentration of the cell is given by 



V 



If the cell was originally in the turgid condition, its osmotic 

 concentration Oi is given by 



where G is a value called the degree of turgor tension, and is 

 the ratio of the volume of the turgescent cell to that of the non- 

 turgescent, but unplasmolysed, cell. 



In these formulae it is assumed that the protoplast con- 

 tracts at the same rate as the vacuole. It is, however, probably 

 more correct to assume that the protoplast does not contract 

 at all during plasmolysis. Accepting this as the true state of 

 affairs, we have in place of the above formula the following : 



= C 



and 0,= O 



where p is the proportion of the whole volume of the unplas- 

 molysed cell which is occupied by the protoplast. 



Should the protoplast change its volume by a fraction ap 

 the first equation becomes 



1 — ap 



The quantity y/ is called by Hofler the degree of plasmolysis. 



In cells of suitable shape which undergo a regular contraction 

 on plasmolysis, it is easy to measure both Fp and F,. In the 

 case of parenchymatous cells from the stem of Tradescantia 

 elongata, G. F. W. Meyer, it was shown by Hofler that the 

 degree of plasmolysis was inversely proportional to the con- 

 centration of the plasmolysing solution in the case of sucrose 

 solutions, varying in concentration from 0*30 to o'6o gram- 

 molecules per litre. With a number of solutions of different 

 concentrations consistent values for the osmotic concentration 



