1. By the use of a special analytical technique it has been possible to study the accumulation of halogens in the cell sap of Nitella.
2. From a dilute solution, Br may be accumulated in the sap in a concentration much greater than that of the external solution. The conductivity of the sap may be markedly increased by such accumulation. The process is a slow one so that a month or more may be required to approach equilibrium.
3. Cl may be lost from the cell as a result of the accumulation of Br and vice versa. Other reciprocal relations between Cl and Br are indicated.
4. At equilibrium practically as much Br accumulated in the sap with an external solution containing 1 milli-equivalent of Br as with one containing 5 milli-equivalents.
5. Light energy was indispensable to the accumulation of Br. The temperature coefficient was characteristic of a chemical process.