242 



Mineral Nutrition of Plants 



O 



CO 



O 



10 



20 



30 



MINUTES 



Figure 26A. Graphs here and in Figure 26B show the absorption at 

 O C. of Rb 86 , P 32 , Sr 85 , and I 131 by apical root segments and the subse- 

 quent release of the elements in exchange for inert isotopes. In 26A root 

 segments 2 cm. in length and about 0.4 mm. in diameter were repeatedly 

 immersed in Rb*Cl or KH,P*C> 4 ; in 26B, in Sr*Cl 2 or KI* solutions. 

 Following each immersion the segments were washed in distilled water 

 and counted (curves A and B). The segments were then transferred to 

 0.005 AT nonradioactive solution of the same salts and the process of suc- 

 cessive immersions repeated (curves C and D). The amount of radicele- 

 ment in each segment is expressed in terms of counts per second.— Over- 

 street and Jacobson ($6) 



