SUMMARY Vesicular-arbuscular mycorrhiza were established in Trifolium parvij7orum in culture by inoculation with Endogone spores. In a medium containing 265 mg. phosphorus (P)/l., as CaHPO, and K,HP04, infection occurred only when the medium lacked nitrogen (N). In a medium containing only roo mg. P/l., infection occurred readily in the presence of 0.5 g. KNO,/I. Calcium monohydrogen phosphate, Ca phytate, Na phytate, Fe phytate, phytin, lecithin and DNA were adequate sources of phosphate for both plant and fungus. Ca phytate and DNA greatly stimulated fungal growth, and DNA also stimulated spore formation, in the agar medium. With Na in the medium infections in the root were sparse. Inositol may serve as a carbon source for Endogone. Mycorrhizal infection occurred with either FeCl, or Fe-EDTA in the medium; when so little iron was present that plants grew poorly, there was also little mycor- rhizal infection.