From the culture medium of Penicillium islandicum, malonic acid was isolated by Yamamoto and later 3-hydroxyphthalic acid by Gatenbeck. However, these acids could not be detected in the present experiments.
Among several organic acids excreted into the culture medium, the substance which is responsible for the pH-change of culture medium was identified paper-
chromatographically as gluconic acid, which seems to have no direct bearing on the biosynthesis of mycelial pigments.