GROWTH RETARDANTS 
The growth retardants are a diverse group of synthetic compounds that reduce stem elongation and generally increase the green color of leaves. These compounds inhibit cell division in the subapical meristem of the shoot, but generally have little effect on the production of leaves or on growth. The physiological effects of the growth retardants can be reversed by application of GA, but generally no other compounds are effective. Incorporation of growth retardants into the media of cultures of G. fujikuroi generally inhibit GA production. In higher plants, the activity of the enzymes involved in kaurene synthesis and oxidation are by Three general classes of compounds have emerged. Compoundssuch as AMo1618 and phosphon D inhibit the enzymes involved in kaurene synthesis, ancymidol and the triazole analogs inhibit the oxidation sequence of reactions. The cyclohexanetriones such as prohexadione-Ca(BX-112) later stages of GA oxidation l). In all three cases the level of active gibberellin reduced. A number of the compounds that inhibit GA biosynthesis also inhibit sterol in plants. There is, however, little evidence that sterols are involved in stem elongation, and it would appear, therefore, that the primary effect of the growth retardant on internode length is due to an inhibition in GA biosynthesis.