Fig. 1. Fitted linear (y = a + bx) or quadratic (y = a + bx + cx2) curves on year of release for (a) combine grain yield (15% moisture content), (b) grains per unit area, (c) ears per unit area, (d) grains per ear (no significant curve; SE of the difference of the means = 2.73, df = 28), (e) harvest aboveground dry matter (DM), and (f) harvest index. Fitted data were 2-yr means for eight cultivars released from 1972 to 1995.