It has been found that rubidium added to the surrounding sea water as RbCl quickly appears in the sap of coenocytes of Valonia, and within 2 or 3 days attains a concentration there which greatly exceeds that in the surrounding medium (Brooks, '32). Although this process has been referred to as accumulation, it is perhaps best to consider it a s an exchange of ions which may or may not be the same as the process by which K, for example, is originally accumulated from sea water by these coneocytic living cells. I n this sense the process is of interest from the point of view of the relative permeability of the protoplasmic membranes of Valonia to different ions, an aspect which has already been reported upon. It is also possible to obtain interesting information as to the role of the protoplasmic layer in the absorption and distribution of ions. This is the subject of the present paper.
METHODS
Material
Valonia ventricosa was collected from the lagoon at Tahiti, was freed from the relatively few adhering organisms, kept at least 24 hours to allow recovery from the effects of manipulation, and then used in the experiments. No differences were observed which could be attributed to the time up to a week or more which was allowed for recovery from the effects of collection and cleaning. Two special experiments were done with plants collected at Tahiti and shipped to Berkeley where 169