In the case of geotropism, the upper side of roots growing horizontally make more auxin. This elongates the top cells, causing the root to turn downward. Gibberellins are hormones that are found throughout the plant. They encourage stem lengthening and the setting of fruit. Many times commercial fruit trees and vines will be sprayed with gibberellins to increase the amount of fruit produced.
Ethylene is a gas that also serves as a plant hormone.
It is usually connected to the ripening of fruit. Another of the important physiological activities of plants is the movement of water throughout the plant. Part of the homeostatic needs of the plant is to keep a certain amount of water in it to maintain cell rigidity and for use in photosyntheisis. The movement of water throughout a plant is called transpiration. The water enter plants through tiny root hairs which may only be a couple of cells thick.