CsCl gradients and DNA hybridization experiments of the kind discussed in chapter 1 do not address whether integrated foreign DNA can be biologically expressed in the plant. If foreign genes were expressed, one would want to know whether they are inherited by the offspring of the transformed plants. For this, classical genetic experiments are needed, in which DNA encoding a trait easily scored is first fed to plants. If this foreign DNA is expressed in a detectable way in the new host, crosses can be made with this transgenic (transformed) plant to study transmission of the new trait and to test whether Mendel's principles are obeyed (or violated). This chapter summarizes the early claims of genetic transformation in plants and their subsequent refutation.
Dieter Hess, now at Hohenheim University in Germany, seems to have been the first person to claim biological and genetic effects of exogenous DNA in plants. The fact that he published most of his results in the German language may have delayed their impact, but eventually his work came to be more widely recognized. Much credit for this gained notoriety should go to Bianchi and Walet-Foederer of the University of Amsterdam, who published in English an extensive summary of Hess's work and critiqued it (Bianchi and Walet-Foederer 1974). As their own article was published in a cryptic Dutch journal, it is mostly through the circulation of reprints that scientists learned about this new controversy.
Hess's early transformation work dealt with the effects of exogenous DNA on flower color in Petunia hybrida and was published between 1969