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Daily Variations in Products of Photosynthesis, Water Content, and Acidity of Leaves Toward End of Vegetative Period

Paul P. Stanescu
American Journal of Botany
Vol. 23, No. 5 (May, 1936), pp. 374-379
Stable URL: http://www.jstor.org/stable/2436100
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Daily Variations in Products of Photosynthesis, Water Content, and Acidity of Leaves Toward End of Vegetative Period
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Abstract

The important daily variations of carbohydrates ordinarily observed in the green leaves occur also in the last days of the vegetative period, and they have the same rhythmic character as during the summer. The curves of the hexose sugars frequently show an opposite course to those of sucrose or starch. This character is particularly marked during the daytime. Toward the end of the vegetative period the beginning of starch accumulation (determined by the iodine test) is generally observed later in the morning than during the summer. The monosaccharides predominate in petioles, starch is second in quantity, and sucrose is found in very small amounts or is often completely lacking. The water content of laminas also presents rhythmic oscillations. In petioles these variations have a much less marked amplitude. The absolute water content of the petioles is always higher than that of the laminas. Water absorption by the tissues is associated with a synthesis of organic substances. A relation between the marked variations of carbohydrates and of the water content and the weak oscillations of the actual acidity is not observed. In the majority of cases, however, a contrast seems to exist between the curves of the acidity in lamina and petiole. Toward the end of the autumn the temperature apparently represents a limiting factor in the sense of Schoder.

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