Abstract: | SYNOPSIS. Synchronization of cell division in axenic cultures of the free-living ciliated eukaryote Tetrahymena pyriformis (W) may be achieved equally as well by a sudden increase in irradiance, DD→LL (switch-up), or by a sudden decrease in irradiance, LL→DD (switch-down), provided that the irradiance transition occurs after a critical time in the late ultradian exponential growth phase. Circadian division indices (~24 hrs) are associated with infradian generation times (GT>>24 hrs). |