In multicellular tissues such as the cortex of roots and the mesophyll cells of leaves, where there are no specialized vascular elements, the pathways for the movement of ions are the symplast and apoplast. Observation of calcium transport in regions where these pathways are physically or physiologically blocked can provide information on the pathways of calcium movement. In roots, calcium movement to the central xylem is heavily reduced in regions where suberization and cellulose thickening of the endodernis constitutes a barrier to apoplastic movement. The implication that calcium moves with difficulty in symplastic pathways in general is supported by the relative immobility of calcium in the phloem, its slow rates of diffusion across layers of cells such as in fruit cortical tissue, and lack of redistribution from aging leaves to other parts of the plant. It is suggested that suberization of bundle sheath cells in many monocotyledons may have a restrictive effect on the transfer of calcium between leaf vascular tissue and surrounding cells.