238 Mineral Nutrition of Plants 



plants, an indirect influence on continued absorption may obtain under 

 certain circumstances. The inhibiting effect of a high-salt condition in 

 roots on further accumulation was pointed out earlier. Transport from 

 root to shoot may lead to a more rapid, continued salt absorption by 

 roots in such a condition. The indirect influence of transpiration in 

 enhancing the rate of translocation in some cases is clear, though 

 probably unimportant under usual growth conditions (12). 



DISTRIBUTION PATTERNS 



The distribution pattern of inorganic solute within plants is related 

 to the relative rates of accumulation by cells, translocation, and growth. 

 This subject will no doubt be presented by Biddulph elsewhere. It may 

 be well, however, to discuss certain observations in this direction. Ac- 

 cumulation of salt in cells, it has been pointed out, is intimately con- 

 nected with permeability and the process of metabolism. The energy 

 supply for metabolic or active accumulation has its source in proto- 

 plasm. It is of interest to see, if possible, whether a process of secretion 

 of inorganic solute from protoplasm to vacuoles or to stelar vessels is 

 concerned (2, 3; compare 46). Using unicellular algae for material, 

 Brooks has shown that accumulation levels of ions are, at least initially, 

 higher in the cytoplasmic fraction (9). Some experiments have indi- 

 cated a higher concentration of certain ions in the vacuolar fluid than 

 that in the residual portion of the cell samples (32). Such results are 

 presented in Table XI. From these data it might be inferred that a 

 secretory process exists. However, this observed difference between 

 lumen and protoplasm is probably related to less obvious moisture re- 

 lations within the protoplasmic fraction (//). Thus, for example, a 

 high nonsolvent water percentage under natural conditions in proto- 

 plasm might decrease the usual solute concentration through dilution, 

 on expression of composite sap from this fraction. In such a way, the 

 observed concentration differences between vacuole and aqueous solu- 

 tion phases of cytoplasm might be of opposite sign from those obtain- 

 ing under natural situations. 



Across the root, the transverse pattern of accumulation level is less 

 known. Some data, including exudates from decapitated plants, may 

 indicate a secretion from living cells to stelar lumina (32). However, 



