Geno- and plasmotypes of variegated pelargoniums

Conclusion

Variegated and periclinal pelargoniums offer some very puzzling problems. Chittenden (1927) collected some of these cases, which, however, have become simplified as the result of my investigations. Two forms of variegation were identified, the one due to sorting out of mixed plastids, and the other to recurrent exomutation of plastids induced by a recessive stimulant gene that is mutable itself. Various plasmotypes of plastids differ in their colour, the degree of crumpling of tissues, and mutability. The plasmotypic change of plastids is either automutable or exomutable, while sometimes the plastids transform in two directions. The white-over-green periclinals generally have albinotic epidermis. In the majority of cases unstable chlorophyll periclinal types change into stable types, probably at the growing points. Freak of Nature, Chittenden’s variety A, and the green crêpe sport from Hanamikado are periclinals with differentiated ectohistogens, it being green in the first named and albinotic in others. The extent to which the respective three histogens contribute to the ontogeny of the plant body is considered from both anatomical and genetic investigations. Since in leaf formation of the pelargonium the ectohistogen develops into the marginal mesophyll as well as the epidermis, the mesohistogen into the outer and submarginal mesophyll, and the endohistogen into the innermost mesophyll, the chlorophyll periclinals with differentiated ectohistogens bear leaves with margins of a different colour.