Abstract
The cellular adjustment of the pH of the external environment of soybean (Glycine max) hypocotyl elongating cells, frequently assumed to be hydrogen ion secretion when the pH is lowered, is unaffected by auxin. These elongating cells actively adjust the external hydrogen ion concentration (from any pH in the range of 4-8) to pH 5.4 + 0.2. This pH adjustment occurs in a medium which does not contain potassium. Growth-optimum auxin concentrations have no effect on cellular pH adjustment of the external medium, whether added at the beginning of the experiment or after the equilibrium pH is attained. The pH adjustment by the cells occurs rapidly and in spite of the presence of a cuticle.