Interaction of Single Tobacco Plants With Direct-Beam Light

Abstract

The interaction of single plants of tobacco with direct-beam light was investigated using coordinate data describing the three-dimensional display of foliage. The projection of unit leaf area of single plants showed little variation with either plant size or azimuth angle of sight but showed a major dependence on the zenith angle. In contrast, the beam-lit area of foliage varied with each of these factors. Zenith angle also had the largest effects on the distribution of beam-lit foliage area with respect to the leaf-beam angle.

These variables were also estimated with a model which took account of the basic structural features of the plants. The assumption of a uniform distribution of the leaf projections on the plane normal to the beam led to systematic errors in estimates of the proportion of beam-lit foliage. These deviations were used for estimates of an empirical index of the dispersion of the projections of the elements of foliage. The index varied with plant size and zenith angle of sight. Satisfactory estimates of the projections of unit leaf area and of distributions of the beam-lit foliage with respect to the leaf-beam angle were obtained from the model orientation distributions and assuming that foliage intercepts light in proportion to its frequency in the orientation distributions. Results are discussed in terms of changes in the structure of the plant associated with growth and development.