In plant tissue water molecules move through two routes apoplasm and symplasm. Apoplast transport is through non-living portion of the plant and symplast is through cell to cell via plasmodesmata. The symplastic (living) pathway to the vascular stele involves cell to cell transport by plasmodesmata. Plasmodesmata are channels of cytoplasm lined by plasma membrane that transverse cell walls. These channels allow to move from cell to cell without passing through the cell wall. Plasmodesmata represent direct cytoplasmic connections from one cell to the next.
The apoplastic (non-living) pathway provides a route toward the vascular stele through free spaces and cell walls of the epidermis and cortex. An additional apoplastic route that allows direct access to the xylem and phloem is along the margins of secondary roots. Secondary roots develop from the pericycle, a cell layer just inside the endodermis. The endodermis is characterized by the Casparian strip, a suberized layer that forces all plants to move in the symplast in order to enter the vascular system. Since secondary roots grow through the endodermis, a direct pathway to the xylem and phloem is available that bypasses the Casparian strip and allows the plants to enter the vascular system without moving into the symplast (living tissue). The non-living portion of plants is called apoplasm, while the entire living portion of the plant forms a continuous single entityand is called symplasm.
Once the water join the symplastic pathway, xylem conduits it spontaneously moves upwards through xylem of root, shoot, petiole and finally in the tracheid of leaf vein and mesophyll cells. Most of the water evaporates from the mesophyll cells and diffuses out to the air through stomatal pore present in the leaves.