Symplastic movement may be aided by cytoplasmic streaming. For e.g., cytoplasmic streaming in cells of the Hydrila leaf, and the movement of chloroplast due to streaming etc.
Most of the water flow in the roots occurs via the apoplast, since the cortical cells are loosely packed, and hence offer
no resistance to water movement. However, the inner boundary of the cortex, the endodermis, is impervious to water,
because of a band of suberized matrix called the casparian strip. Water molecules are unable to penetrate the layer, so they are directed to wall regions that are not suberized, into the cells through the membranes. The water then moves through the symplast, and again crosses the cell membrane, to reach the cells of xylem. The movement of water through the root layers is ultimately symplastic in the endodermis. This is the only way water and other solutes can enter the vascular cylinder.
Once inside the xylem, water is again free to move between cells as well as through them. In young roots, the water enters
directly into the xylem vessels and'or tracheids. These are non-living conduits, and so are parts of the apoplast.
Some plants have additional structures associated with them that help in water (and mineral) absorption. A mycorrhiza
is a symbiotic association of a fungus with a root system. The fungal filaments form a network around the young root
or they penetrate the root cell. The hyphae have a very large surface area that absorb mineral ions and water from a much larger volume of soil, that perhaps, a root cannot do. The fungus provides minerals and water to the roots in turn, the roots provide sugars and N-containing compounds to the mycorrhizae. Some plants have an obligateasso associationh the mycorrhizae. For example, Pinus seeds cannot germinate and establish without the presence of mycorrhizae
