SUMMARYAn examination of the type material ofEndogone fasciculatahas given rise to substantial doubt that the chlamydospores and zygospores included belong to the same species. Therefore, the chlamydosporic sporocarps have been designated as the lectotype for this species.Maize and tuliptrees inoculated withE. fasciculatadeveloped vesicular-arbuscular mycorrhizae. Sporocarps formed in pot culture on or near maize roots. Vesicles in roots and spores borne free in the soil or in sporocarps do not differ in any important respect and are all regarded as chlamydospores. Gaullaud's Arum type of mycorrhiza developed on inoculated maize plants. On inoculated tuliptrees, mycorrhizae very similar to Gallaud's Paris type formed. Vesicles produced byE. fasciculatamechanically damaged the cortex of maize roots. However, maize inoculated withE. fasciculataand grown in soil low in phosphorus produced more than twice as much dry weight as uninoculated maize. Mycorrhizal maize removed more phosphorus and potassium from soil than nonmycorrhizal maize. Tuliptrees grown in moderately fertile soil and inoculated withE. fasciculatamade good growth. Uninoculated tuliptrees grown in this soil remained stunted.