 He remained in Hamburg to complete a doctorate in Botany (plant physiology) in 1978.In 1978 he moved, as an Assistant Professor to the Botany Department at the University of Münster, where he stayed until his appointment as Full Professor and Chair of Botany at the University of Cologne in 1988.In 1982 he was Visiting Assistant Professor at the Albert Einstein College of Medicine of Yeshiva University (Bronx, N.Y.).