Water and minerals are absorbed, and move through all three pathways. Selective transport mechanisms allow minerals to accumulate to hundreds of times their soil concentration in cells of the epidermis and cortex. All water and mineral passing into the stele must go through the endodermis, which acts as the last selective passageway into the vasculature. A belt of suberin in the endodermal cell walls called the casparian strip blocks any other passage. Water flows in from the cortex, generating a positive pressure.
Excess water generated by root pressure at night can escape through leaf valves called hydathodes .
Hydrogen bonding prevents separation of the water column. Adhesion to the vessel walls helps counter-act gravity. Pulling water up the xylem vessel creates a lower water potential in the root xylem which can squeeze the diameter of the vessel walls. This negative potential helps water flow passively from the soil. Control of transpiration.