The word hormone is derived from Greek and means 'set in
motion.' They are naturally produced within plants, though very
similar chemicals are produced by fungi and bacteria that can
also effect plant growth. A large number of related chemical
compounds are synthesized by humans, they are used to regulate
the growth of cultivated plants, weeds, and in vitro grown
plants, they are called Plant Growth Regulators or PGRs for
short. At the beginning of the study of plant hormones,
"phytohormone" was the commonly-used term, but its use is less
widely applied now. Plant hormones are not nutrients, but
chemicals that in small amounts promote and influence the
growth, development and differentiation of cells and tissues.
The biosynthesis of plant hormones within plant tissues is often
diffuse and not always localized, because, unlike animals, which
have two circulatory systems (lymphatic and cardiovascular)
powered by a heart that move fluids around the body, plants use
more passive means to move chemicals around the