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This experiment was conducted to clarify the effect of growth retardants on the morphogenesis and activities of GA-like substances in Bletilla striata in vitro. It was recommended that the desired concentrations of growth reduction in Bletilla striata were below 0.05 ㎎·L^(-1) of uniconazole, 0.2∼0.4 ㎎·L^(-1) of ancymidol and 0.4∼0.8 ㎎·L^(-1) of paclobutrazol. Paclobutrazol showed possibility for use not only as a growth retardant but also a growth promoter because of accelerating effect on both leaf and root growth in the treatment of 0.1∼0.2 ㎎·L^(-1). Besides, some plants treated with high concentrations of ancymidol (0.2∼0.8 ㎎·L^(-1)), paclobutrazol (0.8 ㎎·L^(-1)), and uniconazole (0.20.4 ㎎·L^(-1)) flowered infrequently. Activities of GA-like substances in leaves treated with ancymidol was seldom shown, but in roots, it was higher than the control. Leaf epidermis cells treated with uniconazole became more dense than the control. The number of stomata per unit leaf area was increased, but the total number of stomata was decreased compared to the control because of reduction of leaf area. With the microscopic examination of the longitudinal section of leaf, the number of cell layers was the same as the control, but the cell size was increased and the cuticle layer was thickened by uniconazole treatment.
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