Chapter VII — 83 — Osmotic Quantities of Cells 



and Barlund, 1933; van Overbeek, 1942). Sodium chloride, calcium 

 chloride (and their mixture), glycerin, and urea have also been employed. 

 The time necessary for equilibrium between the cell contents and external 

 solution has been variously reported to be from 20 minutes to 2 hours. 

 Ernest (1935) objects to the plasmolytic method on the ground that there 

 is no critical point for incipient plasmolysis in the plasmolysis-time curve, 

 and that the time necessary for equilibrium may be so great that changes 

 occur, introducing errors. This is opposed by Bennet-Clark, Green- 

 wood, and Barker (1936), who point out that after 30 minutes the amount 

 of water still to be transferred is insignificant. See also Oppenheimer, 

 1936.) Generally, for suitable tissues and under proper conditions, water 

 transfer in plasmolysis tests should attain equilibrium in 30 minutes. Red 

 beetroot cells have been shown to remain in a condition of incipient plas- 

 molysis for 16 hours with no detectable change (Currier, 1944c). 



Penetration of sucrose or loss of solutes are more likely to occur where 

 cells are bathed in hypertonic solutions or pure water than in isotonic 

 solutions (Meyer and Wallace, 1941). Steward (1928) found that 

 potato tissue discs placed even in distilled water failed to lose significant 

 quantities of solutes during reasonably long periods. As an indication of 

 the low permeability of cells to sucrose, Huber and Hofler (1930) cal- 

 culated the permeability of stem cells of Majanthemum for water to be 

 10,000 times greater than for sucrose. 



That adhesion of the cytoplasm to the walls occurs in certain cells upon 

 plasmolysis has been frequently reported (literature by Buhmann, 1935). 

 ScARTH (1923) observed that the protoplast of Spirogyra separated from 

 the wall smoothly when plasmolyzed with salts of monovalent alkaline 

 earths, but di- and trivalent cations increasingly produced adhesion. Ex- 

 posure to very dilute solutions of di- and trivalent salts, followed by plas- 

 molysis in a solution of the monovalent salt, similarly resulted in adhesion. 

 The efifects were reversible and could be removed by washing in water. 

 Methylene blue was found to completely prevent the trivalent salt effect, 

 and to remove the effect once established. Scarth suggested that in some 

 cases the adhesion may be due to the imparting of a positive charge to the 

 cell wall, which would attract the protoplasm, and that this may be accom- 

 panied by changes in viscosity or adhesive properties of the protoplasm. 



Quantitative estimations of the magnitude of adhesion pressure were 

 sought by Buhmann {loc. cit.). Values found for leaves of Rlioeo dis- 

 color were of the order of 1 atm., for Bergenia cordifolia 1-3 atm., Hook- 

 eria lucens 3-6 atm., and for Pinits laricio 5-10 atm. Her method involved 

 1) determination of the limiting plasmolysis value, POg, 2) plasmolysis in 

 hypertonic solution, 3) redetermination of the limiting plasmolysis value, 

 DOg, this time approaching it from the plasmolyzed state, 4) complete 

 deplasmolysis in hypotonic solution, and 5) again determining the limiting 

 plasmolysis, ROg. It was assumed that the POg, DOg, and ROg values 

 should be identical in the absence of adhesion. Actually, POg values ap- 

 peared to be generally higher. ROg values slightly exceeded DOg values ; 

 this was attributed to a new, but weaker, adhesion with the wall. 



Buhmann's adhesion values for beetroot tissue amounted to one to 

 three atmospheres (Table 21). Using the same tissue and a similar tech- 

 nique, one of us obtained somewhat lower values as shown in Table 33, 

 Chapter VIII (Currier, 1944a). A complicating factor in such tests in- 

 volving de- and replasmolysis relates to the extensible nature of the cell 



