Animation of the cellular anatomy of the root of a plant. Roots serve to collect water (red blue) and dissolved nutrients from the soil (brown) and pass them to the rest of the plant. The outmost layer consists of hair cells (red), which are very fine and increase the surface area available for absorption. Water passes into the hair cell by osmosis, and crosses the epidermis (green) into the parenchyma (grey), a large mass of undifferentiated cells that forms the cortex of the root. The innermost layer of the cortex is the endodermis (yellow), whose cells are coated on all sides apart from those facing out and in by a waxy layer, the Casparian strip (blue). This serves to prevent the movement of water laterally between cells, only allowing it to flow from the cortex to the next layer, the pericycle (purple). This is the outer layer of the vascular tissue, which passes water into the xylem. Xylem is the vascular tissue that carries water upwards to the rest of the plant. Although osmosis is important at bringing water into the hair cells, it is the pressure created by evaporation (transpiration) from the leaves that draws water up the plant.