MUCH of our recent knowledge of plant hormones we owe to the Utrecht botanists, whose investigations led to the recognition of the nature and function of these substances. Earlier experiments carried out with seedling oats showed that the shoot apex produced substances capable of regulating growth. When cut off and placed on gelatin, quantities exuded from the tips of the active substances proportional to the number of seedlings used for a fixed period of exudation. These substances could be transferred to other seedlings. A wide search was made for a ready source of these compounds, found to be present in small quantity in grain, pollen and leaves. Higher concentrations are available in urine.