VISCOSITY, PERMEABILITY, PROTOPLASMIC STREAMING 563 



occurred at 625 m-c. The large disaccharide molecules were affected to 

 a greater extent than the monosaccharides. 



Approximately at the same time Steward (1932) studied the effect of 

 light on the intake of bromide ions by potato tissue but was unable to 

 demonstrate any influence. 



In test objects with large cells it is possible to study the permeability 

 by means of a direct analysis of the cell sap. The salt intake of Nitella 

 was investigated in this way by Hoagland and Davis (1923) and by 

 Hoagland et at. (1926). They found that illumination enhanced the 

 intake of chlorine, bromine, and nitrate. Thus the sap of plants that 

 had been exposed to light had a higher content of these substances than 

 did the sap of those which had remained in the dark for a similar period, 

 this varying from a few hours to 5 days. According to the afore-men- 

 tioned authors, this difference was dependent not only on the perme- 

 ability of the protoplasm but also on the abihty of the cell to utilize the 

 light energy for the Avork involved in the transport of salts. 



Hoagland and Davis called attention to the fact that most of the 

 inorganic elements of the cell sap are present in dissociated form and 

 that the cells are able to cause the movements of ions from a solution 

 of low concentration into one of higher concentration. This condition 

 requires that energy relations be taken into account. In other words, 

 the plant must apparently do work in absorbing ions from dilute solu- 

 tions. Hoagland and Davis presumed that, in the case of autotrophic 

 plants, light- either directly or indirectly — is necessary for the process 

 of absorption. This is because light furnishes the ultimate source of 

 energy to the plant. 



Jacques and Osterhout (1934), working with Valonia imder different 

 illuminations and in dark, found that, in all cases in which a pH differ- 

 ence was maintained, the rate of intake of potassium was greater at the 

 higher pH. Since the value of the hydroxyl group just outside the proto- 

 plasm would increase as a result of photosynthesis, they assumed this 

 process to be the primary cause of the phenomenon. 



In a later work Jacques (1939) returned to the same view of the pH 

 effect on rate of intake. He studied the entrance and exit of ammonia in 

 daylight and in darkness, using V. macrophysa as the test object. After 

 exposure, analyses for potassium, sodium, and ammonia were carried out 

 on small samples. He stated that accumulation of ammonia takes place 

 more rapidly in light than in darkness and that the accumulation appears 

 to continue until an equilibrium is attained. He found that the equi- 

 librium concentration of ammonia was approximately twice as great in 

 light as in darkness. According to Jacques, both effects may be due to 

 the fact that the external pH — and hence the concentration of undissoci- 

 ated ammonia — is raised by photosynthesis. 



The exit of accumulated ammonia from the sap of Valonia into normal 



