The Uptake of Cations by Vallisneria Leaves

1. Cations absorbed by Vallisneria leaves could be separated into three fractions, viz: 1. a fraction which was washed out in deionised water (fraction A) 2. a fraction which can be removed by exchange (fraction B) 3. a fraction which can be neither washed out nor exchanged. 2. Absorbed anions could be separated into two fractions only, viz: a fraction A and a fraction C; an exchangeable fraction being absent (chapter n). 3. The formation of the exchangeable fraction B depends on the physicochemical and that of the fraction C on the biochemical properties of the plant (chapter in). 4. It is concluded that a Donnan equilibrium determines the exchangeable fraction B (chapter iv). 5. The transfer of rubidium ions from the exchangeable fraction B to fraction C is strongly affected by temperature and is inhibited by monoiodoacetamide (chapter v). 6. Of each number of rubidium ions accumulated as fraction B (exchangeable fraction) one part is more readily transferred to C than the rest. The rate of transfer of the first part is approximately linear to the number of ions present in B. The second portion is transferred at a much lower rate (chapter vi). 7. In contrast to exchangeable rubidium-ions, exchangeable calcium-ions of the fraction B are practically not transferred to fraction C, though Ca-ions are taken up in C from the external solution. This uptake depends on metabolism. It is concluded that adsorption-exchange in fraction B does not constitute a necessary link in the uptake of cations from the external solution into fraction C (chapter vn). 8. It is made probable that the exchangeable fraction (fraction B) is located in the cell-wall, and that the metabolic process which accumulates cations into the fraction C is located at the outer boundary of the cytoplasm. (Chapter VIII and General Discussion).