1. Causes of aberrant segregation of gene S in the raspberry were investigated in several series of crosses, in two of which auxin was applied to alternate fruits 7 days after pollination.
2. Pollen parents usually had more influence on segregation than seed parents, but the aberrant segregation was probably due to post-fertilisation effects.
3. There was a difference in the seedling emergence time of the alternative phenotypes and failure to emerge probably caused aberrant segregation in some crosses. Variation in seed dormancy was correlated with variation in endosperm size and there was evidence that gene S affected the latter.
4. Aberrant ratios associated with the use of Burnetholm as pollen parent were due to other causes. They were improved by dilution of the pollen which probably reduced competition between pollen tubes of alternative genotype.