The microsporogenesis of the 1st backcross generation of (Oryza sativa X O. officinalis) X O. sativa was similar to that of the F1 of O. sativa X O. officinalis with the rare exception of an extremely long spindle found in the backcross generation. The pairing of the 24 homologous sativa chromosomes in this blackcrossed generation with 36 chromosomes was not constant. On an average, there were only 6.86 bivalents/cell instead of having 12 pairs. The major types of microsporogenesis were studied. The 1st column of the diagram indicated that the expected meiosis takes place in megasporocytes. The backcrossing to recurrent parent might artificially construct O. sativa with the possible 12 individual O. officinalis; chromosomes of some of the ovules produced would have 12 A chromosomes plus one or more C chromosomes. There were few other types of meiosis observed and they were described in detail. Restitution nucleus was formed. These might lead to the formation of unreduced gametes. Again as in the F1 with non-syn- chronization of mitosis and cytokinesis, triads instead of tetrads were formed which in turn lead to the formation of the unreduced gametes.