Abstract
The treatment of root tips of Allium carinatum, Allium cepa, and Allium flavum with colchicine, abscisic acid, kinetin, and indole‐3‐acetic acid, applied in appropriate concentrations, combinations, and durations, makes possible the selective blockade of the cell cycle in G1, G2, any mitotic stage, and between karyokinesis and cytokinesis. Moreover, treatment with abscisic acid followed by a recovery period stimulates polyploid nuclei in mature tissues to divide. Colchicine, kinetin, and indole‐3‐acetic acid applied together cause end‐to‐end association of metaphase chromosomes. These results together with earlier findings suggest that any step of the cell cycle is independently controlled both by specific balance of the growth regulators and by specific synthesis of the nucleic acids.