I n a recent paper, Brooks ( '39) has described rather fully the changes in ion concentrations involved when Nitella are treated with relatively dilute solutions of radioactive ions. It is here proposed to discuss only one phase of this penetration process, namely that designated as "induced accumulation", or the accumulation of ions without the perforniance of metabolic work.
Previously it has been found (Mullins and Brooks, '39) that Nitella lose ions slowly when placed in solutions of 0.02 M sucrose or in distilled water, but that rapid ion loss occurs when cells are placed in solutions of monovalent cations. I n this work, ion exchange experiments were carried out and a number of experimental factors varied such as the time of immersion, the concentration of external ions etc. The methods used were essentially those described in Mullins and Brooks, ibid. The cells used throughout were mainly N. coronata.
DATA
Ion. ezchange rates at various times. I n previously described experiments, Nitella were immersed in radioactive salt solutions (0.01 M) for 15 minutes (when it was supposed that induced accumulation was at its maximum) and then the exchange rates were tested (see table ). I n subsequent experiments 0.01 M Rb*Cl (Rb" connoting the radioactive isotope ,,Rbss) was used and the rate constant of the exchange process, k was measured after immersions of 0.25, 0.50 and 10.0 hours in this solution. At 10 hours there was appreciable Rb" in the sap; but its concentration was only 10% of that in the protoplasm. Figure and table 2 give the k value or rate of loss of Rb" from the protoplasm. This k value is given by equation 1 as representing the logarithmic decrease in ion concentration with time. d In C,, dt k =