These sprays may reduce the apparent rate of photosynthesis of Stayman apple leaves for 3 to 5 days after spray treatment, even though no visible burning occurs. When the maximum temp. reaches 90°-100° F assimilation is usually significantly reduced, regardless of the spray conc. in contact with the leaf tissues. Except for 3 cases in these expts., the rate of photosynthesis of sprayed leaves showed a reduction on the 1st day after treatment; otherwise the reduction in assimilation occurred not later than the 2d day following the spray application.