Mechanical properties of the rice panicle.

Curvature, bending moment, and second moment of stem cross-sectional area were evaluated from photographic data and used to compute flexural rigidity and Young's modulus in the panicle rachis of rice, Oryza sativa L. ;M-101.' Flexural rigidity C, and its components E, Young's modulus, and I, the moment of inertia of the area about the neutral axis, were evaluated 1.5 cm (tip), 9.5 cm (mid), and 16.5 cm (base) from the tip of the panicle rachis. In dynes per square centimeter, C increases from 1.1 x 10(3) near the tip to 1.09 x 10(4) in the middle to 5.35 x 10(4) in the basal region of the rachis. Of the components of C, the I changes have the larger effect, increasing from 2.12 x 10(-7) centimeters(4) near the tip to 8.21 x 10(-7) centimeters(4) in mid regions to 6.0 x 10(-6) centimeters(4) in the basal regions. Young's modulus increases from 4.8 x 10(9) dynes per square centimeter near the tip to 1.4 x 10(10) dynes per square centimeter in mid regions then falls to 7.4 x 10(9) dynes per square centimeter near the base of the main stem. Values of Young's modulus from Instron experiments were in satisfactory agreement with values calculated from the beam bending equation. Flexural rigidity in the curved region of the panicle proved independent of panicle load, indicating that the dissected panicle rachis behaves in some respects as a tapered loaded beam.