The process begins with transpiration at the leaf surface, where water evaporates from the stomata, creating a water vapor deficit in the leaf. This deficit generates a negative pressure or tension in the leaf's mesophyll cells. This tension is transmitted down through the water column in the xylem, all the way to the roots. The cohesive property of water molecules, due to hydrogen bonding, maintains the continuous column of water, allowing the negative pressure to pull water up from the roots.
