T. C. Br oyer 213 



of another salt. The interionic effects observed by Hoagland (26) were 

 concerned with low concentrations throughout, usual to natural con- 

 ditions in soils. Such effects, where more than a single inorganic solute 

 is present in the external medium, are not always of a sort to suggest 

 interionic lowering of energy intensity of constituent ions in the ex- 

 ternal medium nor decreased permeability of the membrane, since 

 reductions in absorption of an indicator ion are not always obtained. 

 On the contrary, under appropriate conditions, the presence of a com- 

 plementary salt may lead to increased inward migration of the primary 



TABLE III 



Effect of a Divalent Cation on Accumulation of Salt and on Respiration by 



Excised Barley Roots 



Accumu- Respiration 



lation Rate 



Experimental Conditions Br* Ratio 2 C0 2 



counts/ 



min./set mm. /h 



r. 



H,0 o 34.0 33.5 



KBr* 0.005 N 334 4- 2 37-5 37-° 



KBr* 0.005 Af+ CaS0 4 0.015 A 7 43° 5-7 4 2 ° 4 10 



External medium 83 



Note: Plants grew in darkness for five days in dilute calcium sulfate solution. Experimental 

 period 8 hours; temperature 20 C. 



inorganic solute ions. Addition of polyvalent cations in appropriate 

 concentrations to a single indicator salt medium may increase the rate 

 of entry of both cation and anion of the inorganic solute in question 

 over the absorption rate from the single component salt solution alone. 

 Figure 16, from Viets (87), shows the increased migration rate of 

 potassium and bromide into roots when calcium bromide is supplied in 

 addition to potassium bromide in the external medium. Similar data 

 for radioactive bromide only are shown in Table III. In addition, these 

 latter data indicate corresponding increases between the indicator anions 

 absorbed and respiration. It may be noted in passing, that this poly- 

 valent cation effect is not observable under environmental conditions 

 which inhibit oxidative metabolism (8y). These results suggest that 



