This book contains the proceedings of a symposium, held in the Limburgs Universitair Centrum, Diepenbeek, Belgium, from July 23 to 29, 1978.1t can be considered as a continuation of the publication 'Environmental and Biological Control of Photosynthesis' (Dr. W. Junk b.v. Publishers, The Hague, 1975). In the last meeting, however, emphasis was much more on the biological control of photosynthesis. The sequence of the different topic sessions and papers on the symposium programme is maintained in the publication; the editors are aware of the fact that different contributions might figure equally well in more than one session. A limited number of speakers was invited; time for discussion therefore could generously be provided to the audience. We thank all the participants for their active contribution to the success of this conception of organizing a meeting. The quality of a discussion session also depends on the performance of the discussion leader; thanks are due to Drs. G. Bernier, J.J. Landsberg, C.J. Pearson, R. Sachs, I.A. Tamas and K.J. Treharne who took the chair with scientific authority and enthusiasm. In order to keep in memory the flavor of this aspect of the meeting, an account of the discussion on one particular topic, the relationship between photosynthesis and flowering, was made by Dr. R. Sachs (reporter) and Dr. G. Bernier (discussion leader) and is published here after the reports on this topic.