There are five major classes of plant hormones (a.k.a. Plant growth regulators (Pgr's)) with perhaps a few others as candidates to take that place in the future. The five major hormone classes are Auxins[?], Cytokinins[?](CK’s), Ethylene, Gibberellins[?] (GA’s), and Abscisic Acid (ABA). Recently it has been suggested that Brassinosteroids[?] (BA’s), Jasmonates[?] (JA’s), Salicylates[?] (SA’s), and Polyamines[?] are new classes of major hormones.
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Source: U.S. Office of the Federal Register (http://www.archives.gov/federal_register/electoral_college/scores.html#1804)
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