SUMMARYExcrescences were observed on hyphal walls ofBipolaris ntaydisgrown under a variety of cultural conditions. These structures were more numerous on hyphae found in the older portions of the colony. By electron microscopy, it could be demonstrated that the excrescence was bounded by a surface pellicle. The latter is an electron-transparent layer which is detectable after its surface becomes coated with electron-opaque material. The pellicle was also found to continue away from the excrescence to form a surface layer over the hypha itself. Presumed young hyphae in the peripheral regions of the colony had neither a pellicle nor excrescences. The presence of a pellicle appears to account for the smooth appearance of the wall surface of older hyphae in contrast to the irregular, frayed appearance of younger hyphae.