Examination is made of some botanical features relating to the applied genetics of raspberries and blackberries (genus Rubus and also of the relative roles of diploidy and polyploidy in Rubus improvement, The germplasm of diploid wild raspberry (R. idaeus) is examined for its possible use in cultivated raspberry improvement, particularly for quantitative characters, but it is considered to be of little benefit. Genetical problems for blackberry (R. fruticosus agg.) improvement at the tetraploid level are demonstrated, particularly in raising larger numbers of seedlings through the increased difficulty of retrieving recessives in a tetraploid F2. A discussion is given of apomixis and the constant species-hybrid, both of which are prominent features of the Rubus breeding-system, and attention is drawn to the possibility that somatic plasticity in perennial Rubi is more frequent than hitherto realised.