Replicate race tubes are inoculated at one end and subject to a 6 hr, 18 hr, and 48 hr artificial day over 7 ordinary days. The clock is manifested by the appearance of orange bands (i.e., asexual production of spores) as the culture grows to the other end of the tube. In each artificial day the race tubes experienced (A) 3 hrs light and 3 hrs dark, (B) 9 hrs light and 9 hrs dark, or (C) 24 hrs light and 24 hrs dark. It can be seen that the number of conidial bands tracked the number of artificial days experienced. Race tubes were prepared as described in [30] and in Materials and Methods and were inoculated using the bd mutation (FGSC 1858).