SUMMARYIncubation of spores ofGigaspora margaritaon agar medium containing activated charcoal resulted in an increased rate of hyphal growth. Circular patterns simulated by hyphal growth from groups of centrally plated spores following germination permitted assessment of“colony”diam. Pretreatment of spores or water with activated charcoal did not enhance fungal growth. These results suggest that an inhibitor of fungal growth is produced or released during and/or after germination.