FIG. 3.

DNA frequency distributions of Prochlorococcus strain MIT 9302 at 1800 to 2100 at division rates of 0.69 div d⁻¹ (30 microeinsteins m⁻² s⁻¹) (A) and 1.34 div d⁻¹ (120 microeinsteins m⁻² s⁻¹) (B). Note that when the division rate is less than 1 div d⁻¹ (panel A), there is no sign of new G₁ cells entering S phase, in contrast to the clearly visible cohort of cells reentering S phase during ultradian growth (panel B).