<P> Plant hormones (also known as phytohormones) are chemicals that regulate plant growth . In the United Kingdom, these are termed' plant growth substances' . </P> <P> Plant hormones are signal molecules produced within the plant, and occur in extremely low concentrations . Hormones regulate cellular processes in targeted cells locally and, moved to other locations, in other functional parts of the plant . Hormones also determine the formation of flowers, stems, leaves, the shedding of leaves, and the development and ripening of fruit . Plants, unlike animals, lack glands that produce and secrete hormones . Instead, each cell is capable of producing hormones . Plant hormones shape the plant, affecting seed growth, time of flowering, the sex of flowers, senescence of leaves, and fruits . They affect which tissues grow upward and which grow downward, leaf formation and stem growth, fruit development and ripening, plant longevity, and even plant death . Hormones are vital to plant growth, and, lacking them, plants would be mostly a mass of undifferentiated cells . So they are also known as growth factors or growth hormones . The term' Phytohormone' was coined by Thimann in 1948 . </P>

The chemicals produced in plants which stimulate growth are called