The history of cytological and genetical studies within the genus Pelargonium, especially P. x Hortorum Bailey, is reviewed, and the practical techniques for handling anal pelargoniums are described. Following the introduction, Part I describes the Mendelian inheritance of alternative traits for characters red spotted pink petals, White-eyed pink flowers, golden leaf, flower doubleness and nectary spur, male sterility, leaf zonation patterns, and flower colours; at least 16 genes are involved. An examination of the extranuclear character plastid inheritance in Part II led to the new hypothesis, that the switch between alternative patterns of plastid segregation after G x W plastid crosses was determined by the presence of both dominant alleles versus absence of either dominant allele of two nuclear genes. Finally, in Part III, many of the genes described in Part I and II are tested in various combination for their independent assortment. The complete linkage of the genes for flower doubleness and nectary spur could not be distinguished from the pleiotropic effect of one gene. There was no evidence for even partial linkage of any other genes.