The flower which remained covered by calyptra after bloom (called hereafter as abnormal flower) tended to occur in 'Kyoho' and 'Pione', and the rates of its occurrence were higher in vigorous shoots showing reciprocal relation to the set of seeded berries. Though the shoot spraying with SADH before bloom promoted the set of seeded berries, the abnormal flowering was not inhibited by the treatment. The cluster dipping with 4-CPA before bloom induced almost complete seedlessness accompanied by the increment of the abnormal flowers. When the normal and abnormal flowers were cohrpared as for the set of seeded berries in the strong shoots, in which the abnormal flowering occurred at relatively high rates, they did not differ significantly each other in all treatments except in the SADH. The number of pollen tubes detected on the cross section of style was smaller in the abnormal flowers than in the normal ones, but no significant difference was found between them in the number of ovules which a pollen tube penetrated. Further, the abnormal flowers were shorter in the length of style, which was a favorable character for self pollination in such a condition. Thus, self pollination is possible in the abnormal flower, and there seems to be little causal relation between the abnormal flowering and the set of seeded berries in 'Kyoho' and 'Pione', eventhough these two phenomena show often a reciprocal relationshrp.