The effects of varying internal and external pH of Valonia upon penetration of arsenic.

A study was made of the penetration into Valonia macrophysa of trivalent and pentavalent inorganic arsenic by changing both the internal pH of Valonia and the external pH of the surrounding solution. The internal pH was decreased by subjecting the cells to NaHCO₃ solution, and increased by treatment with NH₄Cl solution. The external pH was varied from pH 5.0 to 9.0 by adding arsenic adjusted to the desired pH (by adding NaOH or HCl) before the addition of sea water, and kept constant at that pH by the addition of minimal amounts of HCl. The pH determinations were made with indicators. The cell wall, protoplasm and sap were separately analyzed for arsenic. The method of handling and testing the cells was the same as that used in a previous paper. 1

It was found:

1. That the concentration of arsenic in the sap was less than that in the protoplasm. With trivalent arsenic, the difference is less than with pentavalent arsenic.

2. The minimum amount of arsenic penetrates into the sap and protoplasm, when the external solution is approximately neutral.

3. When free CO₂ is alllowed to accumulate in the plant, and the plants are then placed in pentavalent arsenic solutions of various H ion concentrations, more arsenic is found in both sap and protoplasm than in normal plants placed in similar arsenic solutions. When trivalent arsenic is used instead, the concentration of arsenic in the sap is increased, while that in the protoplasm is decreased.