Tobacco plants that are somatic mosaics for the expression of a cytokinin‐synthesizing gene have viviparous leaves. Epiphyllous buds can be either vegetative or floral. Floral adventitious buds can be either normal or abnormal. Abnormalities of floral development correlate with: (i) a local activation of the cytokinin‐synthesizing gene, (ii) a drastic increase in floral cytokinin content, and (iii) a decrease in the steady‐state levels of mRNA homologues of the homeotic genes DEFA, GLO and PLENA of Antirrhinum majus. Thus, these data show in planta that cytokinins, a class of phytohormones, are able to alter the development of floral organs and to decrease the expression of three homeotic floral genes.