Abstract
The level of spontaneous chromosome aberrations and other phenomena concomitant with mitoses in the meristematic cells of Allium cepa L. adventitious roots grown in water, depends to a large extent on the intensity of bacteria multiplication. From the water culture two strains of bacteria, which were most numerous, were isolated - Agrobacterium and Flavobacterium. A supernatant from bacteria grown on Davis medium induced chromosome sticking together, c-mitoses and the formation of polyploid nuclei in the roots of onion.