Comparison of two preparations of Zea mays primary roots has shown that the salt concentration in the xylem fluid is altered as it passes through a region of the root where no absorption of salts or water from the external bathing medium can occur. Salts are secreted to the xylem by such a region, presumably from the vacuoles of the cortical cells. It has also been demonstrated that longitudinal water movement through the root cortex is negligibly small during root-pressure exudation.
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Meiri et al. (1970) studied this question.