T. C. Br oyer 217 



ral, bathing medium. He observed, under comparable external condi- 

 tions, the relative distribution of three monovalent cations in these 

 plants. It was found that the relative accumulation of sodium varied 

 markedly between the various types of plants. These data are presented 

 in Figure 17. The inference which may be drawn from these results is 

 that the sodium concentration was determined not only by the en- 

 vironmental conditions, internal conditions, and rates of processes but 

 limited in extent also by the hereditary potentialities of each species. 



Previous history of tissues 



Further, what a plant may do at any time under a particular set of 

 conditions is preconditioned by both hereditary and physiological fac- 

 tors. Its genetic potentialities are preconditioned by the phylogenetic 

 history of the species. The physiological preconditioning is related to 

 what the plant did during its past ontogenetic development. Thus, cur- 

 rent observations of processes in plants are dependent upon the previous 

 history of its tissues. If, for example, excised roots are low in salt, further 

 solute may migrate inward very rapidly during a subsequent interval 

 of time. With such low-salt tissues, the rate of salt absorption may be 

 as rapid for an excised root system as for entire plants. If, however, roots 

 have accumulated inorganic solutes in the past, under favorable en- 

 vironmental conditions approaching upper limits imposed by their 

 hereditary potentialities, they may be restricted, under such circum- 

 stances, from further accumulation. Such high-salt excised roots are 

 close to their dynamic equilibrium relative to inorganic solute con- 

 centration. Further inorganic solute movement into these organs will 

 depend upon some disturbance of internal conditions. If the organ, by 

 some means, (see discussion of external water supply) is reduced in its 

 inorganic solute concentration, further solute can then be absorbed 

 under appropriate conditions. Translocation of inorganic solutes from 

 root to shoot may accomplish this end. Data from such studies (» 

 are reproduced in Table IV. 



Continued accumulation of inorganic solute is dependent on another 

 internal condition, the supply of adequate amounts and type of sub- 

 strate for oxidative metabolism. The substance of importance in this 

 regard is sugar. During inorganic solute accumulation, there is a con- 



