Within about 10 days after inoculation with Agrobacterium rhizogenes, the vascular bundles of storage root disks of turnip or radish developed small outgrowths with numerous root hairs. Thereafter, adventitious roots (hairy roots) emerged extensively from these outgrowths. The hairy roots which emerged fully supported the growth of host plants, though they lacked geotropism. An excised hairy root could be subcultured as an axenic root culture in the absence of phytohormones. Hairy root cultures with extensive lateral branches grew much more rapidly than those with few lateral branches or ordinary roots. Calli were induced from hairy root cultures in the presence of 2,4-D, and root proliferation from these calli occurred in the absence of 2,4-D. Both the primary hairy roots and the roots which grew from them synthesized agropine and mannopine.