T. C. Broyer 



Active or metabolic accumulation 



201 



Simple diffusion leads toward an equilibrium in which a substance 

 in solution tends to approach equality of concentration within the 

 system. Under appropriate conditions, Donnan phenomena and/or ex- 

 change adsorption may lead toward a condition in which differential 

 accumulation of inorganic solutes may obtain within cells. However, 

 some evidence would suggest that these modes of migration are not all 

 inclusive. A complementary process has been proposed and recognized 

 (//, 2j, 28, 42, 59, j 5, 86), whereby inorganic solutes at least are ac- 



;^ 



© 



Jolution - 

 exchange 



Jur/ace 

 m/pmtm 



Contact 



exchange 



'/jf/uf/on 

 m^e/j 



Figure 7. Diagram of various modes of ionic migration, especially 

 adsorption exchange. — Jenny and Overstreet (jy) 



cumulated within cells of plants. This mode of movement is considered 

 to be directly related to metabolism of the cell and is a polar or "unidi- 

 rectional" migration. Each and all of these modes of accumulation, 

 induced as well as active, are probably involved in variable degrees in 

 the net movement into cells and tissues of plants. In this regard, roots 

 of higher plants are of particular concern initially, since they are the 

 organs concerned primarily with absorption for these species. 



FACTORS DETERMINING RATE AND EXTENT OF INORGANIC SOLUTE ABSORPTION 



Aeration 



There are two main groups of influences which determine the rate 

 and extent of solute absorption. These factors may be due either to 



