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Mechanical Properties of the Rice Panicle ¹

Department of Land, Air and Water Resources, University of California, Davis, California 95616, Department of Chemical Engineering, University of California, Davis, California 95616, Department of Botany, University of Washington, Seattle, Washington 98195

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 10³ near the tip to 1.09 x 10⁴ in the middle to 5.35 x 10⁴ 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 centimeters⁴ near the tip to 8.21 x 10^–7 centimeters⁴ in mid regions to 6.0 x 10^–6 centimeters⁴ in the basal regions. Young's modulus increases from 4.8 x 10⁹ dynes per square centimeter near the tip to 1.4 x 10¹⁰ dynes per square centimeter in mid regions then falls to 7.4 x 10⁹ 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.

¹ Supported by grants from the California Agricultural Experiment Station and PCM 78-23-710 from the National Science Foundation to W. K. Silk and Contract DE-AM06-76 RL02225 from the Department of Energy to R. E. Cleland.

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