Absorption of Phosphate and Potassium Ions in Poplar Stems

Phosphate and potassium ions were drawn through segments of poplar stem using a vacuum. Analysis of the activity-time curves for selected points along the stem were consistent with a mathematical model of mass flow combined with irreversible lateral flow along the conducting vessels. However, the phosphate ion could be flushed out of the stems with water, so that it was necessary to consider this as a limiting case of a reversible-flow model. Comparison is made with the activity-time curves for ion absorption into plant tissue, which are considered similar in shape. A value of 50 μm min−1 was obtained for the lateral velocity, and the ratio of tracer lost laterally to tracer moving on along the pipe was calculated to be about 0.7