688 



PLANT GROWTH AND PLANT COMMUNITIES 



Mechanism of transfer. In the contact zone, the carboxyl groups 

 may react with iron oxide as follows: 



COOH /COO. 



/ / \ 



Root-COOH + Vz FeoOa ^^^ Root— COO— Fe + IV2 H2O 



COOH ^COO'^ 



The H-root surface becomes an Fe-root surface, either as Fe+ + + 

 or Fe++ or as a complex Fe-OH cation. The Fe ions migrate into the 

 interior of the root via exchange di£Fusion with H ions, which move 

 from the interior toward the outer boundary. Should Fe diffuse mainly 

 as ferrous ions, a current of reducing electrons would have to migrate 

 from the interior to the surface. 



The influx of iron must have been accompanied by an influx of 

 calcium ions, according to the reaction: 



Root 



/ 



COOH 



\ 



+ CaCOa 



i^ Root 



,coo. 



COOH 



^COO'^ 



Ca + H2CO3 



The two equations gain support from Grunes's observation (Grunes 

 and Jenny, 1960) that only hydrogen surfaces will decompose haema- 

 tite particles; sodium and magnesium surfaces are ineffective. The ex- 

 istence of counter-flow may be demonstrated analytically by pressing 

 a Ca-amberplex membrane to one of hydrogen. Analysis of exchange- 

 able calcium and hydrogen in both membranes discloses equivalent 

 transfer in opposite directions (Glauser and Jenny, 1960b). For root 

 and milieu the counter-flows of ions may be as follows : 



inside 



