Comparisons of pyrene set were made between raspberry flowers pollinated with undiluted pollen and others pollinated with pollen diluted with talc, or killed pollen. Pollen dilution reduced set but the reduction was not the same for all maternal parents. It also reduced the rate of fruit ripening, increased the proportion of pyrenes without seed content and reduced the tendency for abortive carpels to develop into small empty pyrenes. Observations of numbers of pollen grains germinating in the styles revealed differences attributable to the maternal parents, the pollen germinating poorest on the parent whose pyrene set was reduced most by pollen dilution. There were also maternal x paternal interaction effects on pollen germination. It is concluded that pollen germination was conditioned by growth substances provided partly by the grains themselves and partly by the styles of the seed parent, and that there were inter actions between the two sources. Reduction in pollen concentration affected several aspects of early fruit development, but quantitative differences in the amount of pollen applied did not reduce the adverse effects of using diploid pollen. This suggests that such effects do not arise through direct action of the pollen on the maternal tissues.