Chrysanthemum, ‘#3 Indianapolis White’, subjected continuously to atmospheres containing 1-4 ppm ethylene failed to initiate and develop flower buds under short day conditions. The plants showed typical epinastic symptoms, shortening of internodes, thickening of stems and loss of apical dominance. The plants developed many short axillary shoots, each with a few small leaves. The top leaves on the plant became smaller and smaller and were less dissected than the controls. Subjecting plants alternatively to ethylene containing and normal atmospheres generally prevented flowering also, but occasionally crown budding occurred. Bioassay of endogenous auxins showed that these growth promoting substances were maintained at high levels in the ethylene treated plants, which may account for their failure to flower. In addition, ethylene also seemed to affect the polar auxin transport system of the plant.