Before revision: The movement of water out of the leaf stomata sets up a transpiration pull or tension in the water-column in the xylem vessels or tracheids.
After revision: At night when the stomata are closed, water pressure can build up in the plant, and excess water is excreted through pores known as hydathodes.Guttation: A Pressure Relief for PlantsThe movement of water out of the leaf stomata sets up a transpiration pull or tension in the water-column in the xylem vessels or tracheids.