Microsporogenesis was studied in 12 American commercial potato varieties. All of them were characterized by the formation of tn valents and quadrivalents at diakinesis and metaphase I of meiosis. Nine quadrivalents were observed in a microsporocyte of ChippeWa. The maximum number of quadrivalents per cell observed in a coichicine-induced autotetraploid of a diploid species was eight. The varieties studied had several meiotic abnor malities and varying degrees of pollen abor-tion. All produced seed when Katahdin was used as the pollen parent. It is suggested from the results that S. tubersum originated as an autotetraploid.