A large, yellow, one-celled spore 291-812[mu] in diameter was found to be common in Illinois field soils. Spores were separated from soil by wet sieving and decanting. They were surface sterilized and pure cultures were obtained. Cultures made only limited growth on all media tested. When spores were used to inoculate plant roots they produced a mycorrhizal infection of the phycomycetous type. Arbuscules were produced in abundance; however, vesicles did not form. Following penetration compact clusters of echinulate spores formed on the external mycelium. Cross inoculation experiments utilizing spores obtained from near corn and red clover roots indicated a wide host range.