| Acidity fluctuations typical of Crassulacean acid metabolism (CAM) were observed in flowers of CAM orchids such as Arachnis, Aranda, Dendrobium and Vanda hybrids, but not in flowers of a C3 orchid, Oncidium Goldiana. The range of fluctuation was however, much smaller in the flowers than in the leaves. Dark 14CO2 fixation yielded labelled malate while day fixation resulted in labelled intermediates of C3 photosynthesis. A diurnal CO2 production rhythm was observed in flowers of both CAM and C3 orchids irrespective of fragrance production. |