1. A method is given for the determination of the cation exchange capacity (CEC) of small quantities of Sphagnum material (50-100 mg of dry weight, dead material). The method is especially suitable for measurements with bivalent cations. 2. Branches and stems of Sphagnum plants have very different CEC. 3. Under the given conditions the CEC is 11,7 mequiv/100 g of Sphagnum for the monovalent cations Na+ and K+ and 23,3 mequiv/100 g of Sphagnum for the bivalent cations Ca++ and Mg++. 4. When mono-and bivalent cations are mixed (both 0.01 N), the CEC of the monovalent cation decreases to 1/7-1/40 of the CEC in pure monovalent solution; the CEC of the bivalent cation decreases only very little. 5. The CEC increases with decreasing amounts of Sphagnum in a constant volume of salt-solution; on the other hand it increases with decreasing volumes of salt solution containing a constant amount of Sphagnum. 6. Dead and living material have the same CEC (referred to dry weight). 7. Two methods are given for the separation of the total cation contents of living Sphagnum into the contents of the adherent water, of the cation exchanger and of the living cell. 8. Living Sphagnum contains most of the K+ and Na+ within the cells, Mg++ partly in the cells, partly in the exchanger, and most of the Ca++ in the exchanger. 9. Living Sphagnum seems to be able to keep the cation contents of the cells rather constant even when the contents of the adherent water and of the exchanger are varying widely. © 1968 Springer-Verlag.
