10. Studies of some of the Iowa inbred lines showed that in those inbreds which are poor pollen producers there was a considerable number of unpaired chromosomes at Metaphase I. These unpaired chromosomes undoubtedly cause some of the sterility found in these lines. Fertile inbred lines showed fewer univalent chromosomes. In the "sterile" inbreds the pairing pachytene was perfect and the unpaired homologous chromosomes showed at diakinesis an orientation to each other because of this earlier association.