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SUMMARY

Secondary xylem tissue of Coleus and Helianthus internodes, and both parenchyma and vascular tissue of Zea and Triticum coleoptiles, were found to be capable of active polar auxin transport; pith parenchyma from Coleus and Helianthus internodes was not. Electron microscopy revealed the presence of ‘plasmalemmasomes’ in parenchyma cells from tissues known from present and previous work to contain the transport system, and their absence from cells of tissues known to lack the transport system. A possible link between the presence of plasmalemmasomes and the capacity for polar auxin transport is discussed.