Abstract: This paper is a further research on the origin of gynogenic structures of rice which have been induced by the method of unpollinated ovary culture in our laboratory for several years. Three cultivars were used as materials. The culture medium and technique were basically the same as in previously reported experiments. Samples were fixed, stained and sectioned by paraffin method. All the four components of embryo sac could be induced to division, however, with different frequency and results. Most of the gynogenic proembryos were originated from the synergids. The processes of synergid apogamy are described in detail. The egge cell, in contrast, usually vacuolated considerably and underwent free nuclear division, leading to coenocyte formation. The problem of why and how synergid apogamy takes place in such high frequency in ovary culture is discussed. The anomalous behavior of the egg cell is discussed in relation to the physiological as well as the phylogenetic aspect.