Root cells expend energy during the night to pump mineral ions into the xylem. The endodermis prevents leakage of these ions back out of the stele. Accumulation of minerals in stele lowers water potential, and water flows in. This creates a pressure that pushes water upwards and is called root pressure. Branching, root hairs, and cortex cell walls provide large surface area for mineral ion and water uptake.
Transpirational pull takes place at the leaves.
Mesophyll cells are coated with a film of water. The meniscus will have the tendency to become less concave because of the surface tension of water. This tendency to reduce the surface area creates a pull. The cohesion of water due to hydrogen bonding enables transpiration to pull water up the narrow xylem vessels and tracheids. Secondary cell walls are hardened with lignin and fuction as support.