Cells (BF305-15d, HWL148, HWL145, and HWL146) were transformed with an empty vector (pBA70, grey line) or the same vector carrying an insert with four tandem copies of an SBF binding site (“pSCB”) (pMT3579, black line). Cells were grown to early log phase, and fractionated by centrifugal elutriation. Fractions containing small unbudded cells with a mode volume of about 20 fl were chosen and re-inoculated. Cell size (x-axis, in fl) and budding (y-axis, percent) were followed with time. The median experiment of five total wild-type experiments is shown in the upper left. “Critical size” was defined to be the size (in fl) at which 50% of the cells became budded. This critical size is shown next to each curve.