Three pseudogamous Rubus species were pollinated by their own pollen, and by pollen from R. nitidioides. Two of the apomictic progenies from self-pollination were weaker than the corresponding pollinations by R. nitidioides. This was also reflected the following year in their later flowering and in the proportion that flowered.
Pseudogamous R. laciniatus was pollinated by a polyploid series of apomictic species. There was an improvement in early germination and in first-year germination with increase in the ploidy of the pollen parent; but pollination by the sexual diploid R. ulmifolius gave the most vigorous germinations.
Generally there was marked stimulation of the pseudogamous vigour of the apomictic progenies of R. laciniatus from pollinations with other species. This is termed pseudogamous heterosis, It varies with the pollen source, and is affected by the degree of ploidy and genetic differences between the pollen parents.
The pollen parent affects seed shape in R. laciniatus. Lengths and breadths of seeds were correlated for most cross-pollinations, but self- pollination may reduce the correlation through increasing the variation in seed shape, particularly their lengths. This could be related to the sexuality of the endosperm in pseudogamous Rubi.
The occurrence of sexuality in R. laciniatus was tested by pollinations with British species of known taxonomic position. Lidforss’ conclusion was confirmed that the frequency of sexual seedlings is not related to the relative taxonomy of the parents. The sexual hybrids are generally weaker than the apomicts.