Pycnothryria of Tubakia dryina on naturally infected sweet gum (Liquidamber styraciflua) leaves were examined using transmission electron microscopy. The conidioma was attached to mycelium within the leaf tissue by a multicellular columella. Columellar cells were multinucleate. The surface layer of the pycnothyrium, the scutellum, was composed of thick walled prosenchymatous hyphae. Numerous conidiogenous cells were associated with the ventral surface of the scutellum and the columella. Conidia were produced enteroblastically from conidiogenous cells exhibiting a prominent collarette at their apex.