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A method of extraction of tracheal sap from shoots of apple-trees in quantities sufficient for analysis is described. Total solids, conductivity, nitrogen, phosphate, potassium, and magnesium levels were determined in saps from trees of a single variety on different stocks through one season. A marked seasonal fluctuation in levels of each of the four elements was noted.
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E. G. Bollard (1953) studied this question.
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