SUMMARYDevelopment of the protuberant conidial hilum, an important characteristic in the genusExserohilum, is markedly affected by temperature. Temperatures higher than 28 and 34 C inhibited the formation of protuberant conidial hilum inE. turcicumandE. rostratum, respectively. InE. pedicellatumprotuberant conidial hilum formation was partially inhibited at 34 C. These critical temperatures for inhibition of protuberant hilum coincided with those for inhibition of sporulation by light. Continuous light had no discernible effect on the development of hila, except for the stimulation of production of protuberant hila at 24 C inE. turcicum.