A Physoderma found parasitic on Asclepias incarnata L. is noteworthy for the behavior of its zoospores from epibiotic sporangia. These, which bore either a colorless or ochraceous salmon colored globule, apparently lacked the capacity to produce new epibiotic sporangia and exhibited a marked tendency to fuse in pairs. The fate of the fused product could not be followed directly. Seedlings exposed to these, however, eventually had formed within them the polycentric endobiotic system bearing resting spores. The latter germinated after dehiscence of a lid. There is some evidence for believing the fungus is confined to Asclepias.