Abstract
Applications of various amounts of GA3 onto the shoot apex of biennial rosette-plantHyoscyamus niger L., exposed to long days and non vernalized, caused internodes formation and stem elongation. The stem length was proportional to the amount of GA3 applied. Number and length of developed internodes and the whole length of the shoot were maximal in plants treated with a greater amount of GA3. In the end, stem elongation stopped and plants formed perchedrosettes without flowering. Hence, gibberellic acid participates in mechanisms of flowering only by indirect effect on stem elongation and not directly on flower formation itself.