Abstract

During the last fifteen years, a large number of chemical compounds capable of inducing, even in very minute amounts a variety of effects on plant growth and development, have been discovered and also synthesised. These are known by the general name of growth-promoting substances, auxins or phytohormones. A hormone is any substance that can act as a "chemical messenger", which, after being produced in any part of the living organism, is transferred to another part and there influences a speci- fic physiological process. This term 'hormone was first used in connec tion with plants by Fitting in 1910, who showed that the shedding of flowers in orchids soon after flowering was brought about by the presence of the pollen grains and could also be effected by water extracts of the pollinia. The terms "Wuchsstoff", growth-regulator, growth-substance, growth-promot- ing substance, growth-hormones, plant-hormones, phytohormones and auxins, all refer to the same group of substances, so far as they relate to the plant kingdom. The literature on this subject has become very, voluminous within the last ten years and is still growing rapidly. Extensive reviews on the effects of these growth hormones, chiefly upon the rooting of plant cuttings, and curvatures in the oat coleoptile have been published by Went and Thimann (1937), Pearse (1939) and Nicol (1941) The present article is intended as a review of progress made on certain other effects of these auxins with special reference to the growth and yield of crop plants.

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