ABSTRACT
A Committee of the American Society of Plant Physiologists published the nomenclature of chemical plant regulators in 1954, in which plant hormones and auxins are defined. An auxin was the first plant hormone to be chemically identified, and auxins played important roles in early research on plant hormones because they were the sole type of hormone available for plant physiologists to use in their physiological studies until gibberellin was recognized as a second type of plant hormone. Anti-auxins, which competitively inhibit the actions of auxins, have been discovered through biological studies on synthetic auxins and related compounds. Natural anti-auxins also have been isolated from higher plants and fungi. The diversity of the biological activities results from the nature of plant tissues to which auxins are applied and the concentration of auxins. Different tissues respond differently to the same concentration and the same species of auxin.
