254 Mineral Nutrition of Plants 



ion is formed it can attract one additional negatively charged particle; 

 that may be an electron as in the above case, or it may be an anion 

 equivalent (A~). The A~ may denote any mineral anion. As soon as 

 ferrous iron is oxidized by giving off an electron and becomes trivalent, 

 it can bind an A~. That implies that there may be an exchange on the 

 iron atoms of electrons for anions. The iron loses one electron and 

 attracts one anion. 



To explain the transport of the anions through the cytoplasm, 

 Lundegardh assumes that there are tracks or bridges of cytochromes 

 arranged in transverse direction across the cytoplasm between its outer 

 boundary, called the o-level, and the inner boundary, the /-level, which 

 may be the toiioplast or central parts of the organ. Along these tracks 

 the anions are moved by successive exchanges for electrons. At the 

 o-level the anion is attracted by a ferri-cytochrome. This then takes 

 up an e~~ from an inner cytochrome, loses its anion, which is caught by 

 the second cytochrome, and so on. In this way the anion moves from 

 one iron atom to another through the system. 



Lundegardh suggests that there are waves of electrons going from 

 the i- to the o-level and, if such a transport of electrons occurs, anions 

 can be moved in the opposite direction. At the /'-level the anions are 

 released from the cytochromes and given off to the vacuole. It is of 

 course impossible, for electrostatic reasons, for a single anion to be 

 released unless it be combined with a partner having the opposite 

 charge, a cation. The anions are thus combined with cations at the 

 /-level. The cations may be hydrogen ions or more likely metal ions, 

 which are abundantly present, and thus the salt becomes stored in 

 the vacuole. 



The cations can easily be bound to the cytoplasm, because we know, 

 especially from Lundegardh's determinations of the surface potentials 

 of the cytoplasm, that it has a predominantly acid character. It con- 

 tains abundant acid groups with dissociating hydrogen ions, and at 

 these loci, metal cations can be adsorbed by an exchange for the 

 hydrogen ions. I have already mentioned that there are good reasons 

 to assume that in the first step of the absorption the cations really are 

 attached to the plasma by such an adsorption. Lundegardh now as- 

 sumes that the cations are transported through the cytoplasm by re- 



