“…2. A strong decrease in net photosynthesis of the fumigated plants occurred within the first 20 min of exposure to so2 and stable rates were obtained within 2 h. This pattern is in agreement with the results of Sij & Swanson, 1974;Black & Unsworth, 1979b;Barton et al, 1980;Sisson, Booth & Throneberry, 1981;Darrall, 1986). Because steady photosynthetic rates were obtained after a short fumigation period, it can be concluded that the concentration of toxic intermediate oxidation metabolites (sulphite, bisulphite) also reached stable values.…”