VISCOSITY, PERMEABILITY, PROTOPLASMIC STREAMING 559 



and Desmodium. His results could be interpreted on the basis of the 

 assumption that the changes in light gave rise to changes in the perme- 

 abiUty of the plasmatic membranes. These changes in permeability 

 would, in turn, lead to changes in turgor and the known turgor move- 

 m.ents of the leaves. Lepeschkin extended his experiments to other test 

 objects such as Spirogyra and the epidermal cells of Rhoeo. Since he 

 found similar changes in permeability, he considered that the sensitivity 

 of the permeability to light is not specific to the cells of the pulvini but 

 that it is a general phenomenon. 



In his first experiments Lepeschkin used three different methods to 

 demonstrate the effects of fight upon the permeability of protoplasm. 

 The first comprised a determination of the amount of substances diffusing 

 into water from the pulvini. The concentration of cell sap in slices 

 immersed in water was observed with the second method. The most 

 important method was that of the isotonic coefficients, since this was 

 subsequently used by many other investigators who worked on the prob- 

 lems of permeability. 



Experiments with Plasmolytic Methods. Lepeschkin compared the 

 experimentally found isotonic coefficient for the plasmolytic medium 

 with that calculated theoretically. He considered that, if the coefficient 

 found was greater than that calculated, it would imply that the plasmo- 

 lytic substance had penetrated into the cell. The difference between 

 the coefficients would then be a measure of the permeabifity of the cell 

 to the substance in question. Lepeschkin found this difference to be 

 accentuated by fight. 



At approximately the same time, Trondle (1910) reported experi- 

 ments that substantiated the accuracy of Lepeschkin's conclusions. In 

 Trondle's experiments, made on leaves of Buxus and Tilia and carried 

 out with the method of coefficients, an association was also found between 

 the permeability (to sodium chloride) and fight. In the dark, perme- 

 ability was very slight; it increased with a certain intensity of light and 

 decreased with still stronger light, this decrease continuing with even 

 more powerful illumination. He also found that the illumination with 

 an electric lamp of 32 cp at a distance of 10 cm from the plant first 

 resulted in an increase in permeability, followed by a decrease if the 

 illumination continued for more than 1 hr. In a later publication (1918) 

 Trondle repeated his earlier experiments and also tested another method. 

 This was based on the determination of the quantity of salts taken up 

 by the test object per unit of time. The results of these experiments 

 supported his earlier conclusions. 



Fitting (1915, 1917, 1920), who made a thorough study of the plasmo- 

 lytic method, introduced several improvements. Instead of the isotonic 

 coefficients, he made use of deplasmolysis. Provided that deplasmolysis 

 takes place owing to penetration of the plasmolytic substance into the 



