Auxins are the driving force behind plant tropisms. A tropism is when a plant grows in a certain direction in response to environmental factors. In the case of phtotropism, more auxin is made on the shaded side of the plant, causing those cells to elongate, and thus the whole plant bends toward the light. 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.