Microclimate and Plant Growth in open-top Chambers : Proceedings of a workshop jointly organised by the Commission of the European Communities and the Kernforschungszentrum Karlsruhe (Projekt Europäisches Forschungszentrum für Maßnahmen zur Luftreinhaltung), Freiburg 17-19 September 1986 : Microclimate and Plant Growth in open-top Chambers