The marine alga Valonia macrophysa contains in its cell sap K and Na in the proportion of 5.72 to 1. In a form regarded as closely related, Valonia ventricosa, growing in similar environment, the ratio of K to Na is as 0.0278 to 1. The former contains no Mg but in the latter it is present. There are other differences in the composition of the sap.
These differences bring about a remarkable contrast in behavior in that Valonia ventricosa floats in sea water while Valonia macrophysa sinks.