Sap concentration and inorganic constituents of mature citrus leaves

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Introduction

Previous investigations, Haas and Halma,⁽²⁾ on the sap concentration and inorganic constituents of citrus leaves suggested the need for further data as regards seasonal fluctuations. In general the sap of immature citrus leaves is very dilute and becomes more concentrated as the leaves become mature. It appears that the sap of mature leaves increases in concentration as the season advances and that the highest concentration is reached in the winter. The supposition prevails that the sap concentration remains at this level until the leaves absciss. It will be shown, however, that the high sap concentration during the winter months is only transitory and that it is probably related to ineffective translocation of elaborated food rather than to increased age of the mature leaves. As the tree becomes active in the spring, the leaf sap concentration decreases to approximately the same level as that reached during the previous spring when the leaves were mature, but a year younger; in other words, fluctuations in sap concentration of mature leaves is seasonal. On the other hand, the changes that occur in inorganic constituents of similar leaves appear to be related to the age of the leaves rather than to seasonal changes.