Fig. 4. Path diagram describing the interrelationships between spikes m^–2 (1), panicles m^–2 (2), kernels spike^–1 (3), seeds per panicle (4), kernel weight (5), seed weight (6), grain yield (7), and seed yield (8) under the small seed size class. Single-headed arrows indicate path coefficients between variables i and i' (P_ii', i > i') and residual coefficient in variable i (E_i). Double-headed arrow indicates simple correlation coefficient between the exogenous variables (r₁₂). Arrow thickness indicates the magnitude of the effect; broken arrows describe the effect of spring wheat on wild oat and broken-segmented arrows describe the effect of wild oat on spring wheat. *, ** Statistically significant at the 0.05 and 0.01 probability levels, respectively.