Growth Hormones

The word 'hormone' was first coined by Starling in 1906, in the context of animal physiology. In plants, the internal chemical factors that influence growth -- by inhibiting, promoting or otherwise modifying it -- are called growth hormones, growth regulators, or phytohormones. According to Thimann and Pincus (1948), plant hormones are organic substances that occur naturally in higher plants, affect growth or other physiological processes at a site away from where they are produced, and are active in very small (optimum) amounts. Hormones are generally transported through the phloem parenchyma. Of the recognised phytohormones, auxins, gibberellins (GA) and cytokinins (CK) act mainly as growth promoters, while ethylene and abscisic acid (ABA) act mainly as growt …