Morphology-based erythrokinetics. CD34⁺ cells from 3 separate donors were cultured in EPO (A) versus EST (B). On days 0 to 14 (x-axis), differential counts of Giemsa-stained cells were enumerated. The mean percentages of each cell type are shown on the y-axis. Undefined blasts (▤), preproerythroblast/proerythroblast (▦), basophilic normoblasts (▥), polychromatic normoblast (□), and orthochromatic normoblasts (▪) are indicated.