I n a recent paper (Brooks, '35) I pointed out the active role of the protoplasm of the marine alga Valonia ventricosa in the accumulation of rubidium, and probably also other alkali metals, notably potassium. Rubidium entered the protoplasmic layer, reaching concentrations greatly exceeding those in the sea water or the sap of the large cells or coenocysts. From the protoplasm the rubidium normally passes on into the sap. When injury transpires the rubidium is released by the protoplasm and goes into both the sap and the surrounding sea water. I n time it is eventually distributed in all phases, the cell being now dead.
Recently many elements have been made radioactive, including potassium and sodium. Such elements can be followed by measurement of their radioactivity by the use of a Geiger-Miiller 'counter. ' The problem of chemical separation and estimation of these elements has been obviated, since small amounts can be estimated quickly by this method. We have first attempted (Brooks, '37) to follow the intake of potassium, using Nitella clavata, an alga, which, like Valonia, has relatively large cells with a single large vacuole and a thin surrounding layer of protoplasm and a cell wall. We have used radioactive KCll which contains 17C136 o r 17C138 and IRK4'. The C1 breaks down to essentially stabile lsA36 or lsA38, giving off 0 particles, and has a half-life of 35 minutes. The 19K42 'KCI was obtained from the Radiation Laboratory of the Uiiiversity of California through the kindness of Prof. E. 0. Lawrence. I am also indebted to Dr. B. G. Hurst f o r the preparation of the radioactive KCl, and to ?Hr. Dean Cowie f o r valuable assistance in coiistructing a Geiger-Miiller counter.