In The Study of Gene Action, Bruce Wallace and Joseph O. Falkinham III review the problems that confronted geneticists in successive eras. New technologies, developed to solve the problems, inevitably stimulated an awareness of subtler problems that awaited still more sophisticated technologies. The rediscovery of Mendel's studies of inheritance in 1900 catalyzed two branches of research: an investigation of the physical nature of the gene and an elucidation of the means by which the gene performs its function. In The Search for the Gene, Wallace described efforts to identify and characterize the physical basis for the phenomena Mendel observed. The Study of Gene Action, the companion volume, documents the research, accelerating over time, to specify how genes carry out their functions. Initially limited to an examination of external features and subsequently to classical genetics and cytogenetic analyses, research was revolutionized by Watson and Crick's discovery of the double helix structure of DNA. The domain of genetics became inseparable from chemistry, biochemistry, and molecular biology.