Plant hormone concepts and hormone experiments for the high school level
Buoscio, Alfred Anthony
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Among the substances which markedly influence the reactions and metabolism of the animal body are those internally-produced compounds called hormones. Many of the hormones of the higher animals are secreted by the ductless glands; examples are adrenalin, thyroxin, and insulin. Within the last decade or two convincing evidence has accumulated that hormone-like substances also occur in plants. Those compounds are called growth substances, hormones, growth hormones, or phytohormones. Like animal hormones plant hormones quite commonly affect parts of the organism other than those in which they are produced. It is a characteristic of both plant and animal hormones that they usually exert their physiological effects while present in minute concentrations; it is principally on this basis that they differ from compounds ordinarily classified as foods. ”The starting point for growth-substance investigations was the demonstrations of a growth-promoting material in the tip of the Avena coleoptile, as shown by phototropic curvature. Historical evidence indicates that the growth-substance explanation of phototropism and geotropism had its origin many years ago. About one quarter of a century has elapsed since a hypotheses was displaced by the effect of unilateral light, or gravity (Boysen Jensen). Other contributions to the solution of the problem followed (Paal, Stark, and Seubert). A new impetus was given to the subject when Went (1927, 1928), published his method of procedure for extracting growth substance and demonstrating the quantitative relationship between it and growth in the Avena coleoptile. An ever increasing fund of knowledge about hormone activity is continually extending our understanding of tropisms and the whole problem of normal growth."