Plant hormones are natural chemicals produced in minute quantities in one part of a plant and have a physiological effect when moved to another part of the plant; a chemical messenger. Hormones control growth or other physiological functions such as root initiation, flowering, fruit drop, etc. Unlike animal hormones, phytohormones are not produced in individual organs, but are produced by every cell at various times during a plant’s growth cycle. They are necessary for communication in plants because plants do not contain nervous systems. Naturally-produced hormones are properly called hormones or phytohormones. There are three major groups of plant hormones:
Auxins are plant hormones that influence cell enlargement, root initiation, and bud formation. They suppress the initiation of lateral buds.
These messengers cause cells to elongate. When cells elongate on one side of a plant only, they cause the plant to bend. The elongation is irreversible and widely used in horticulture and agriculture. Perhaps one of the most familiar uses is in the elongation of green grapes, which provide growers with more fruit substance per bunch.
The common rooting hormones available in most garden stores all contain auxins in minute concentrations. Auxins, usually indole-butric acid, are formed naturally in fruits, seeds, pollen, growing points, young leaves and developing buds. Auxins cause cells to grow and especially to elongate & auxins promote apical dominance.
Keikiroot with a minute concentration of the auxin has been found advantageous for orchid root initiation and development.