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The objective of this study was to examine seasonal changes in specific leaf weight (SLW) of soybean (Glycine max [L.] Merrill) leaves and to compare these with changes in leaf area, thickness, and anatomical features. For individual leaves, SLW generally decreased as leaf area increased, and then increased as leaves thickened. In most cases, leaves thickened after the period of greatest leaf area expansion. Specific leaf weight then decreased as leaves senesced. In general, the maximum SLW achieved by each leaf was successively greater with each successive node. Similarly, leaves at upper nodes were thicker than those of the lower nodes. Leaf thicken. ing was largely the result of concurrent thickening of palisade and spongy mesophyll tissues. An important discovery was that in the uppermost, thickest leaves a third layer of palisade mesophyll cells was formed 'by ~iericlinal division in the outermost palisade layer. The nal SLW and leaf thickness obtained were modified by solar radiation levels during the period of leaf development. Differences in radiation distribution seemed to accentuate differences among leaves in 1976 studies and reduce differences in 1977.

The objective of this study was to determine the variability in specific leaf weight (SLW) of 373 soybean [Glycine max (L.) Merrill] lines, to examine the seasonal changes in SLW, and to determine the consistency in the ranking of selected lines over a 3‐year period. Consistency in these data would provide a basis for selecting lines for further, intensive physiological study. The SLW was sampled in the field with a leaf punch on the uppermost fully expanded leaf that was in full sunlight. For the whole collection, SLW was sampled at two growth stages, R2 (full‐bloom) and R5 (beginning to mid‐podfill). The mean SLW increased between these stages from 3.08 to 6.46 mg/cm2, while the standard deviations were 0.36 and 0.77 mg/cm2, respectively. Significant differences among lines were found at both growth stages. Chlorophyll deficient genotypes generally had low SLWs, while dwarf types were high. Cultivars derived from ‘Harosoy’ had significantly higher. SLWs at R5 with a mean of 7.12 than those derived from ‘Lincoln,’ mean of 6.24 mg/cm2, respectively. For 20 lines in 1976 and 10 in 1977, SLW was sampled on a weekly basis. We saw an increase in SLW from flowering to after mid podfill, and then a sharp decline. The SLW at R5 in 1975 correlated well with maximum SLWs in 1976 and 1977. Solar radiation levels influenced SLW. We found a linear relationship between the mean SLW at each sampling date and the radiation received in the week before sampling at R2 in 1975, and maximum SLW was significantly affected in 1976 and 1977.

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