Fig. 2. Regression of percent pollen viability to seeds per boll for four different pollen viability assays. Three-parameter logistic curves were fit to data. Each data point represents the pollen viability and corresponding seed set per boll for one of the four methods. Equations of curves and R² are as follows: B & K method, y = 155.9/(1 + (x/27.2)^-1.29), R² = 0.57; Alexander stain, y = 150.9/[1 + (x/15.3)^-0.74], R² = 0.61; B & K + aniline blue method, y = 237.8/[1 + (x/68)^-0.95], R² = 0.47; and FCR method, y = 103.3/[1 + (x/20.8)^-4.3], R² = 0.63.