This volume offers an account of the scientific outcome of a Priority Programme (Schwerpunktprogramm) which the Deutsche Forschungsgemein schaft (DFG; German Research Society) promoted during 6 years from 1976 to 1982. In the understanding of the DFG, a Priority Programme involves the financing and coordination of research efforts of a group of investigators, possibly from several institutions, and is in tended to concentrate on one particular topic and/or on one maJor area of interest over a period of, as a rule, 5 years. Discussions on the feasibility of a major programme on vertical move...