AbstractTwo diallel crosses between red raspberry parents were made and auxin applied to alternate fruits 7 days after pollination. In a diallel made in 1964 interaction effects between pollen and the maternal effect considerably influenced the set of pyrenes, but maternal effects predomin ated in a diallel made in 1965. Application of auxin in the first diallel reduced the interaction effects, It is postulated that the set of large pyrenes was largely determined by the interaction of physiological effects contributed by the male and female parents, but that maternal effects were so strong in the second diallel that variations in those of the male parent were less important. These factors were probably concerned with the arrest of flower growth and its sub sequent recommencement following pollination. Auxin apparently affected late acting factors associated with seed tissues, but these were relatively unimportant for pyrene set. Self pollination inproved the set of pyrenes in the first diallel, perhaps because the conditions were similar to those under which the varieties were originally selected. Maternal parents differed in the rate at which their fruits ripened, but the pollen parent also influenced the rate of ripening.