In vitro erythropoiesis from normal human CD34⁺ progenitor cells. (A) through (D) show Wright-Giemsa–stained cytospins at serial time intervals of cultures initiated with purified normal human bone marrow CD34⁺cells. Culture conditions used to induce erythroid differentiation are described in the Materials and Methods. Enucleated RBCs are marked with arrows. All photographs were taken at original magnification × 200. (A) Day 7; (B) day 9; (C) day 12; (D) day 19.