The term auxin is derived from the Greek word auxein meaning to grow. Auxins may, and generally do, affect other processes besides elongation, but elongation is considered critical.
Auxins are generally acids with an unsaturated nucleus or their derivatives.
IAA was first discovered in human urine. Since this time there have been numerous reports indicating that IAA is found ubiquitously within the plant kingdom. In addition, it has been shown that IAA is synthesized in numerous species of nonseed plants including bacteria, fungi, and algae. It is generally accepted that IAA is synthesized from tryptophan in pollen and actively growing tissues such as shoot meristems, leaf primordia, young expanding leaves, developing seeds, and fruits. Auxins are involved in many physiological processes in plants.