Chapter VII 



87 — Osmotic Quantities of Cells 



results from the dissociation of the former into ions resulting in a greater number of 

 solute particles per unit volume. With sucrose taken as one, Fitting (1917) calcu- 

 lated isotonic coefficients of many solutes by comparing their ability to produce limit- 

 ing plasmolysis in leaf cells of Rhoeo discolor. Table 24 lists some of his values, as 

 well as those calculated from freezing point measurement. There is good agreement 

 in most instances. De Vries used this method to determine the molecular weight of 

 raffinose. 



Further Uses of Plasmolysis: — In addition to osmotic pressure 

 measurements, the plasmolytic method may be used in permeability studies 

 to determine the effect of solutes on the behavior of protoplasm, and as a 

 criterion of the physiological state of cells. 



Fig. 22. — Plasmolysis types as illustrated by Strugger 

 (1935). Convex plasmolysis, a; concave plasmolysis, b; 

 "krampf" plasmolysis, c and d. 



The form which the cytoplasm assumes upon contraction and separa- 

 tion from the wall is usually indicative of its viscosity (Weber, 1924), 

 which in turn may reflect other conditions in the cell. Its form is also re- 

 lated to the nature and concentration of solutes in the plasmolyzing solu- 

 tion, and often is characteristic for any one type of cell. Figure 22 illus- 

 trates some of the forms which have been described. Convex plasmolysis 

 (Figure 22a) is attended by, or is the result of, low viscosity, and the 

 separation from the wall appears to progress smoothly and without per- 

 ceptible adhesion. It is generally observed in normal uninjured cells, and 

 particularly in mature cells. Concave plasmolysis (Figure 22b) indicates 

 a relatively high viscosity, w^here the separation occurs with more difficulty. 

 The form identified as spasmodic ("Krampf") by the German workers 

 (Figure 22c and d) is an advanced concave type which indicates an even 

 higher viscosity. Weber (1925) made the interesting observation that 

 guard cells of Vicia faba in the closed condition exhibit a convex form when 

 plasmolyzed, while those in the open condition showed the concave or 

 spasmodic form. 



Several forms of plasmolysis are allegedly due to differential permeabil- 

 ity of ectoplast and tonoplast. Solutes may diffuse into the protoplasm but 

 not into the vacuole ("Intrabilitat"). 



