Abstract
Desmarestia viridis（Phaeophyceae）accumulate a highly acidic substance in the vegetative cells of the thallus. Prior attempts to clarify the intracellular locality of the acidic substance have been inconclusive until now. As a result of D. viridis cell observation using an optical microscope, neutral red indicating an acidic compartment accumulated in vacuoles. Vital staining by the pH indicator bromophenol blue showed the strong acid accumulated in the vacuole. Furthermore, methyl violet showed intracellural pH was approximately 1.0, and accorded with past results that were derived from inorganic ion concentration.
