Abstract
When the living cells of Nitella are placed in a solution of brilliant cresyl blue containing NH4Cl, the rate of accumulation of the dye in the sap is found to be lower than when the cells are placed in a solution of dye containing no NH4Cl and this may occur without any increase in the pH value of the cell sap. This decrease is found to be primarily due to the presence of NH3 in the sap and seems not to exist where NH3 is present only in the external solution at the concentration used.