The Production and Distribution of Dry Matter in Maize after Flowering

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Abstract
An experiment in which different groups of leaf laminae were removed, or ears shaded, shortly after silking showed that most of the dry-matter increase after flowering was produced by upper leaves. The top five, the middle four, and the bottom six laminae accounted, respectively, for 26 per cent, 42 per cent, and 32 per cent of the leaf area duration (D) of the laminae after flowering; the estimated contributions of the three groups to dry-matter production by the laminae after flowering were about 40 per cent, 35–50 per cent, and 5–25 per cent, respectively. The sheaths provided about one-fifth of the total leaf area and probably contributed about one-fifth, and laminae four-fifths, of the total dry matter produced after flowering. The contribution from photosynthesis by the ear was negligible, presumably because its surface area was only 2 per cent of that of the leaves. Leaf efficiency (dry matter produced per unit area) decreased greatly from the top to the base of the shoot. When laminae were removed, the grain received a larger fraction of the dry matter accumulated after flowering, less dry matter remained in the stem, and the photosynthetic efficiency of the remaining leaves was apparently increased. When alternate laminae were removed at the time of silking (half-defoliation) D was decreased by 40 per cent, and the subsequent production of dry matter decreased nearly proportionately, so that net assimilation rate (E) was not affected but grain dry weight was decreased by only 32 per cent. At the final harvest, the grain of half-defoliated plants constituted 80 per cent of the dry matter accumulated after flowering, compared with 65 per cent for intact plants. Stem weight decreased from two weeks after flowering in half-defoliated plants, but remained nearly constant in intact plants. When pollination was prevented and no grains formed, E during the first month after flowering was unaffected; the dry matter that would have passed into the grain accumulated in the stem and husks, not in the leaves. The decrease in stem weight caused by defoliation suggests that previously stored dry matter was moved to the grain. That such movement is possible was shown by keeping prematurely harvested shoots in the dark for two weeks with their cut ends in water; the dry weight of the grain increased and that of the stem, laminae, husks, and core decreased. Nevertheless, dry-matter production after flowering was more than sufficient for grain growth, and previous photosynthesis probably contributed little to the grain.