In the course of cytological studies of the genus Azotobacter, large bodies, buds, L colonies, and other peculiarities were observed in one particular strain, Azotobacter agile M.B. 4.4. The balloon shapes that have received attention in recent literature (Dienes, 1946; Shanahan et al., 1947; Tulasne, 1949a) were especially abundant among these morphological oddities. It should be emphasized that, unlike other strains of Azotobacter (Eisenstark et al., 1950), variety A. agile M.B. 4.4 does not go into an encysted stage. This strain is morphologically stable and rarely varies from the typical single and paired forms (figures 1 and 2) when grown on the usual laboratory nitrogenfree media. Even very old cultures contain only these regular cell types. However, when cells are transferred from a nitrogen-free medium to a medium containing ' This research was supported by the Research Foundation of Oklahoma Agricultural and Mechanical College.