Regeneration of buds, shoots, and roots in cells and explants in vitro has provided useful developmental systems to analyze the processes of cell differentiation and morphogenesis. Interest in these studies was greatly stimulated by the demonstration of chemical regulation of morphogenesis in 1957 by Skoog and Miller (1). They showed that a high ratio of cytokinin to auxin-stimulated formation of buds when these chemicals were provided in the culture medium. Subsequently, their observations have been applied, extended, and found general application with numerous genera and species.