Figure 2. Correlation between the ratio of constant fluorescence and the peak of variable fluorescence (O/P) and chlorophyll content expressed as percentage of control (plants not exposed to heat) in the flag leaf from 12 cultivars of winter wheat. Data from five replicate plants of each cultivar were averaged and used for correlation analysis. Plotted data are from Experiment 1; n = 12. Similar results were obtained in a duplicate experiment. HS, heat stress.