It was pointed out by Katagiri and Nakahama that the useful retling bacteria acted selectively on vegetable fiber materials and also they proposed that this selectivity was based on the specificity of protopectinase of the bacteria, and that the two characters might have certain parallel relation with each other. The result of the further experiments carried out by the author with mulberry-tree bark also confirmed the selectivity of some kinds of retling bacteria, but found no remarkably different action on protopectin from mulberry-tree bark. Accordingly no parallel relation between the selectivity of the retling bacteria and the specificity of the protopectinase was identified.