Cultures from field collections of Septoria avenae Frank produce "wild type" colonies of rather uniform appearance—a creamy-white mycelium, a brown substrate, and few, if any, pycnidia. Subculturing on potato sucrose agar usually leads to the production of a great variety of variants that fall into two broad classes: mycelial and pycnidial, the latter usually producing scant mycelium, many pycnidia, and a blue-green substrate pigment. In some cultures, staling, i.e., cessation of growth, occurs commonly but is generally followed, after an interval of time, by renewed growth. Cultures of the pycnidia! type show a marked tendency to produce mycelial type variants and, conversely, cultures of the mycelial type will give rise to pycnidial type variants. In certain cultures, strains have arisen that predominantly produce small pycnidia containing spermatium-like microspores, but which are still capable of producing macro-spores. Cultures from microspores show several distinct types including dark-pigmented cultures, albino cultures with dark pycnidia, albino cultures with colorless pycnidia, and cultures of purely mycelial type. Attempts to demonstrate that the microspores perform a function in the production of the perfect stage of the organism were unsuccessful.