Once inside the stele, water is again free to move between cells as well as through them. These are nonliving conduits so are part of the apoplast. The Pathway of Minerals Minerals enter the root by active transport into the symplast of epidermal cells and move toward and into the stele through the plasmodesmata connecting the cells. At any level, the water can leave the xylem and pass laterally to supply the needs of other tissues. At the leaves, the xylem passes into the petiole and then into the veins of the leaf.
Water leaves the finest veins and enters the cells of the spongy and palisade layers.
Here some of the water may be used in metabolism, but most is lost in transpiration. The mechanism is based on purely physical forces because the xylem vessels and tracheids are lifeless. Roots are not needed. This was demonstrated over a century ago by a German botanist who sawed down a 70-ft oak tree and placed the base of the trunk in a barrel of picric acid solution. The solution was drawn up the trunk, killing nearby tissues as it went.