VISCOSITY, PERMEABILITY, PROTOPLASMIC STREAMING 50 i 



plasmolytic method. Riihland (1912) studied the permeability of leaves 

 of Beta vulgaris to glucose and fructose both in sunlight and in darkness. 

 Plasmolysis covered a period of 24 hr. In general, it was not possible to 

 establish any definite and measurable increase in the permeability under 

 the' influence of light, but some of the experiments possibly pointed in 

 the same direction as those of Trondle. 



Ruhland and Hoffmann (1925) used Beggiatoa as the test object. They 

 were also unable to find any definite effect of light. Meindl (1934), on 

 the other hand, found that the permeability of Elodea to urea was up to 

 50 per cent higher in sunlight than in darkness. 



A modification of the plasmolytic method is based on the plasmometric 

 method of Hofler (1918). It consists in the observation of the rate of 

 deplasmolysis during the slow penetration of a substance in the solution. 



Hoffmann (1927) used the afore-mentioned method in an investigation 

 of the effect of light on the permeability of the cells of Spirogyra to 

 glycerol. He found that it was approximately 20-30 per cent lower in 

 the dark. 



Hofmeister (1935) made use of the same method in a study of the 

 intake of glycerol and urea by Zygnema. He was unable to establish 

 any effect of light on the intake of these substances. 



Wahry (1936) tested the permeation of about twenty organic sub- 

 stances in the submerged and aerial leaves of Hippiiris, using the plasmo- 

 metric method. His experiments showed that, as a rule, light hastened 

 the penetration of these substances into the submerged leaves, whereas 

 the effects varied in the case of the aerial leaves. The intake of certain 

 substances was increased in light, in others there was a decrease, and in 

 some cases the intake was unaffected. Thus the reaction differed in the 

 two types of leaves. Jarvenkyla (1937) raised the objection to this 

 investigation that the experiments had not been performed under uni- 

 form conditions of illumination, that no parallel experiments had been 

 made simultaneously in light and in darkness, and that therefore they 

 could not be considered as comparable. 



Experiments with the Turgor Method. Important contributions to the 

 study of the effect of light on the permeation both of water and of solutes 

 have been made by L. and M. Brauner. M. Brauner (1932) initiall}- 

 used the same test object as Lepeschkin, i.e., the pulvini of Phaseolus 

 multiflorus. She studied their reaction to light in several media, such as 

 air, water, cane-sugar solution, and paraffin. The changes in the turgor 

 of the cells of the pulvini were used as an indicator of the intake of water 

 by the cells. She found that the direction of the photonastic reaction 

 was dependent on the suction force of the medium. Thus unilateral 

 illumination with 1000 m-c caused a positive reaction in air but a negative 

 one in paraffin and in water. Because the turgor of the illuminated side 

 decreased in air but increased in both the liquid media, it was concluded 



