T. C. Br oyer 215 



studied with relation to inorganic solute absorption and the concomi- 

 tant respiratory activity. It has been shown that mycorrhizal roots ex- 

 hibit a greater rate of respiration than comparable nonmycorrhizal 

 organs. A higher level of inorganic solute accumulation is attained 

 where this symbiotic association exists. Whether the increased rate of 

 inward migration of inorganic solute is related to a greater surface ex- 

 posure to the root medium, to increased permeability, or to a differential 

 metabolic rate has not been established (^9). 



Hereditary limitations 



In addition to the external or environmental conditions, there are 

 internal controlling conditions which may determine the rates and ex- 

 tent of inorganic solute absorption. These two groups are not wholly 

 mutually exclusive, but the latter are dependent upon the former in 

 many cases. Thus, the factors of aeration and temperature, for example, 

 while applicable to discussion as external conditions altering rates of 

 processes, also alter the internal conditions where, perhaps, they may 

 be more aptly recognized as effective. 



Of particular concern are the hereditary potentialities of the indi- 

 vidual which are predetermined by its ancestry. These potentialities 

 limit and determine the physico-chemical conditions and the extent to 

 which internal processes may proceed. The specific structure, implying 

 the molecular structure and arrangement in protoplasm, with all its 

 inherent potentialities, is relatively constant for each elementary species. 

 This concept is strikingly exemplified in the differential movement of 

 inorganic solute ions and their accumulation within specific organisms. 

 Thus, although exposed to like external conditions, two distinct genetic 

 types of plant may exhibit markedly different permeabilities to, and/or 

 net influx levels of, inorganic solutes. In Table I, it may be seen that 

 Halicystis ovalis and Osterhoutii display salt concentrations in their 

 vacuolar fluids which are quite distinct one from the other, each charac- 

 teristic of the species under their similar natural conditions. Environ- 

 mental conditions may alter internal conditions and processes within 

 an organism, but the extent of the effect will be limited by its genetic 

 potentialities. Thus, in one experimental study, Collander (18) exposed 

 the roots of various species of plants to a common, yet perhaps unnatu- 



