Any substance or mixture of substances intended, through physiological action, for accelerating or retarding the rate of growth or maturation or for otherwise altering the behaviour of ornamental or crop plants or the produce thereof, but not including substances intended as plant nutrients, trace elements, nutritional chemicals, plant inoculants or soil amendments.There are several phytohormone groups; the best known is the auxin group. In plants, phytohormones control the intensity of metabolism, the production of other phytohormones, production and decomposition of pigments, displacement of certain substances into certain organs or storage in them, elongation of the cell wall, the development of flowers, and also growth and growth rate. Это и многое другое вы найдете в книге Interaction between auxin and Vigna radiata L. under cadmium stress (Mohd Mazid and Taqi Ahmed Khan)