1. Methods are described for obtaining cell sap from Nitella without contamination.
2. Tests of the cell sap show that in a balanced solution of NaNO3 plus Ca(NO3)2 there is a slow penetration of NO3 and that the cell remains in a normal condition, but in pure NaNO3 there is rapid penetration accompanied by injury.
3. Inasmuch as determinations of electrical conductivity give the same result it may be concluded that this method gives reliable information regarding permeability.
4. While observations on recovery from plasmolysis give similar results, the method is less satisfactory.