630 BIOLOGICAL EFFECTS OF RADIATION 



60 min. illumination the permeability was 75 per cent below that of the 

 controls, as in the time curves of Trondle. 



Kisselew (188) and Lvoff (246) were primarily interested in the 

 interpretation of the opening of stomata as an action of light on the 

 permeability of the guard cells. The former tested the guard cell 

 permeability to dyes, diastase, saltpeter, sucrose, and by estimation of 

 the rate of plasmolysis, to water. In all of Kisselew's measurements, 

 the guard cells of open stomata showed a reduced permeability. Light 

 is the agent that commonly induces stomatal opening. Lvoff measured 

 isotonic coefficients in the leaf cells of Runiez, using controlled illumina- 

 tion. His results contradict those of Kisselew. He discovered that 

 illumination caused a 60 to 100 per cent increase in the permeability 

 coefficient of the guard cells, and a smaller but noticeable increase in /x in 

 the neighboring cells. This author, and later Lepeschkin, criticize 

 Kisselew's use of starch digestion as a measure of the penetration of 

 KNO3; but Kisselew used other methods, as noted, and particularly the 

 rate of plasmolysis, which (according to this author) is a sounder measure 

 of permeability than the isotonic coefficient (cf. Stiles, 349, page 20), 

 although its application is to water penetration. 



A more exact osmotic method, the Hofler plasmometric method, was 

 used by Hoffmann (154) on Spirogyra cells. The Hofler method con- 

 sists of following the rate of deplasmolysis or reversal of plasmolysis when 

 cells are immersed in a solution of a substance which penetrates slowly. 

 Hoffmann found that Spirogyra cells in daylight showed 60 per cent 

 higher permeability to glycerin than those in the dark. Considering 

 possible errors, Hoffmann states that the permeability increase in the 

 light is at least 20 to 30 per cent. Cells without nuclei behave in the 

 same manner as normal cells. 



Although plasmolytic methods such as that of Hofler are very much 

 in favor at the present time, the results they give are not to be accepted 

 unreservedly. The experimental studies of Weber (388) indicate clearly 

 that in some cases, at least, the plasmolytic method does not provide a 

 measure of the normal permeability of the cell but rather the permeability 

 as altered by the plasmolytic agent. Here again the release of free 

 electrolytes noted above may be a factor; Iljin (169) found that immer- 

 sion of cells of Iris in isotonic salt solutions, particularly Na salt solutions, 

 caused an increase in the osmotic pressure of the cell interior with respect 

 to the cell membrane. Furthermore, Weber (388) has presented evi- 

 dence that plasmolysis always implies a rupture of the cell membrane, 

 which reforms very rapidly if Ca is present. 



Various authors have attempted to determine the influence of light 

 upon exosmosis of substances. Lepeschkin (218) placed pulvini of 

 Phaseolus in water for a fixed period of time, some in daylight, some in 

 darkness, and then analyzed the water for total solids. About 1.5 to 2 



