T. C. Broyer 235 



concentrations of inorganic solutes in vacuoles. Such solute must have 

 passed across the intervening protoplasmic layer from the external 

 medium. Depletion of salts accumulated in the roots is possible through 

 translocation to the shoot. Part of this solute may be transported from 

 vacuoles as well as from protoplasm of a particular cell. Certain ex- 

 perimental observations suggest that the inorganic solute need not 

 move across cells by way of the vacuole. On the contrary, wherever 

 continuity of protoplasm exists — some workers suggest a "symplast" or 

 protoplasmic continuity throughout the plant — inorganic solutes may 

 move along this pathway as well (j, //). 



Numerous interrelations, relative to inorganic solute absorption and 

 translocation, exist between the roots and shoots of plants. A suggestion 

 has been made that light may indirectly control the absorption and 

 retention of inorganic solute by the roots of plants. Lepeschkin (41) 

 has proposed a contrasting formation and destruction of compounds 

 within shoots, in dark and light, respectively, which may alter the 

 differential permeability of roots. The loss of inorganic solutes from 

 roots in relation to the illumination of shoots has been reported by 

 others (/, 48). That accumulation and retention of inorganic solute 

 may be indirectly related to illumination was recognized early. In 

 these latter experiments with algal cells, the effect was considered to be 

 concerned directly with carbohydrate supply, which, as has been pointed 

 out earlier, may control the rate of accumulation under certain circum- 

 stances. Although the carbohydrate factor is recognized, some still 

 consider a possible secondary effect of illumination on salt level in roots. 



There are pronounced effects of various substances on growth and 

 metabolism. The levels of auxin, produced in shoots and transported 

 to roots, can modify conditions and processes in the latter organ. Al- 

 though a direct effect of auxin on inorganic solute accumulation by 

 roots has not been clearly shown (47), modification in the rates of 

 exudation and the inorganic solute concentrations therein imply some 

 indirect effect on salt migration (75). This may be through permeabil- 

 ity phenomena, but further evidence is necessary to this point. Possibly 

 data are even now available to clarify these effects and they may be 

 elucidated in another monograph on hormonal phenomena. 



A number of experiments indicate a close interrelation between root 



