Over street and Dean 



93 



the combinations RK, RNa, R'Cl, R'l, R'H,P0 4 , etc., represent 

 chemical attachments. It would be extremely difficult to interpret the 

 two-way movement of ions characteristic of the isotopic exchange re- 

 actions on the basis of a mere physical entrapment. 



It must be concluded further in the light of the exchange experi- 

 ments that the various combinations represent either different chemi- 



Live Roots 



TIME IN MINUTES 



Figure 2. Graphs showing the exchange for inactive isotopes of I 131 at 

 O C. for live and ether-killed roots. The percentage of the initially ab- 

 sorbed activity remaining in the root is plotted against time. — Jacobson and 

 Overstreet (23). 



cal entities or at least similar complexes with widely varying energies 

 of formation. 



Finally, it must be concluded that the binding complexes are rather 

 labile, since the mere injury or killing of the tissues is sufficient to de- 

 stroy them. 



The idea that ion absorption is chemical in nature is not in conflict 

 with a number of absorption theories that have been put forth — some of 

 long standing. Some of these postulations are of particular interest here. 



