CHAPTER 6 



STRUCTURAL ASPECTS OF SALT 

 ABSORPTION IN CELLS 



When new appearance is before the eyes, 

 New suppositions thereupon arise. 



C. Morton (1687). 



A. Location of Absorption Mechanisms 



1. Early Observations 



Early investigators of ion absorption viewed the cytoplasm 

 simply as a membrane across which transport into the central 

 vacuole occurs. Thus, they disregarded the morphological 

 complexity of protoplasm (Plate I) and ignored the possibiUty that 

 salts may be accumulated within it. Briggs (1932) was among the 

 first to call attention to the retention of ions in cytoplasm, and later it 

 became possible to investigate the situation experimentally using 

 algae with large cells. Brooks (1940) immersed Nitella plants in 

 salt solutions containing radioactive isotopes of alkali metals for 

 varying lengths of time and then determined the radioactivity of 

 cellulose walls, protoplasm and vacuolar sap separately. The wall 

 fraction attained an apparent concentration of salt similar to that 

 of the medium immediately upon immersion, and a few minutes 

 later the concentration of radioactive ions in the protoplasm was 

 several times higher than that of the medium. Entry into the 

 vacuolar sap proceeded rather slowly and little or no radioactivity 

 was detected there several hours after immersion (Fig. 34a). Similar 

 results were obtained in experiments with radioactive bromide 

 (*^Br). Hoagland and Broyer (1942) confirmed the rapid movement 

 of ions from the medium into the protoplasm of Nitella and its slow 

 transference into the sap. In contrast to Brooks, they found that 

 when the experimental period was prolonged, the apparent con- 



95 



