ABSTRACT
Since the dawn of agriculture, one of principal aims of human beings has been the control and promotion of plant growth to satisfy human needs. These two important aspects of people’s work with plants in the struggle to increase production are by no means synonymous. Humans soon realized that lush green growth does not always produce the best crop in the form of fruit and seeds and hence were forced to evolve such well-known cultural methods as pruning, balance manuring, and mineral fertilizers to regulate the nature and luxuriance of plant growth. This control of the plant development pattern-this adjustment of balance between root and shoot and between leaf and flowering-was until about seven decades ago mediated by appropriate and very large empirical combinations of what may be called dietary and surgery. More than 60 years ago proof was given of what Julius Sachs [1] in 1880 postulated: that endogenous substances regulate the growth of various plant organs. In 1926, Went [2], in Holland, provided convincing evidence of a diffusible substance (auxin) from oat (Avena sativa) seedlings that promoted growth of these seedlings. At the same time, Kurosawa [3], in Japan, discovered another substance (gibberellin) from cell-free fungus (Gibberella fujikuroi) filterate that promoted growth of rice (Oryza sativa) seedlings. But it was not until 1955 that Skoog and his associates [4] discovered kinetin in an autoclaved sample of herring sperm DNA, which was active in what Wiesner in 1892 called cell division factor [5].
