SUMMARYEmploying various reagents to dissolve or to digest portions of the teliospore ofTilletia contraversaKühn in conjunction with histochemical procedures, the morphology of the spore was determined and the parts were separated mechanically. The teliospore wall consists of several distinct layers, incorporating a sheath, a reticulum and a two-layered endospore. The reticulum is cemented to the endospore by a lipoid-containing material.By chemical tests and histochemical techniques, the chemical composition of the various layers was defined in part. The sheath was primarily a pectic material complex, incorporating hemicelluloses (including callose) and lipoids (possibly phospholipid in part). The reticulum contained pectic materials, hemicelluloses (including callose), proteins, melanin pigments and lipoids (possibly phospholipid in part). The material cementing the reticulum to the endospore contained lipoids. Other constituents of the material could not be defined as separate from other layer materials, although chitin was indicated. The outer endospore layer was primarily chitin, but some hemicelluloses (including callose in immature spores and sterile cells) were defined histochemically. The inner endospore layer contained at least chitin, hemicelluloses and pectic materials. Callose and protein were probably present but were not distinct from adjacent structures in the tests employed. The protoplast contained pectic materials, proteins, hemicelluloses (including callose in immature spores and sterile cells) and lipoids (mostly ergosterol).