Mycobacillin adheres to the surface of seed or seedling but is not absorbed by rice plant tissue, whereas versicolin not only adheres to the surface but is also absorbed and subsequently translocated. The antibiotic re-extracted from the versicolin-treated plant tissue inhibits the growth of Helminthosporium oryzae. Thus mycobacillin is active only topically, while versicolin both topically and systemically. © 1979 Taylor and Francis Group, LLC.