For example, the tumor-inducing (Ti) plasmid of "Agrobacterium" and the root-tumor inducing (Ri) plasmid of "A. rhizogenes" contain genes that are capable of transferring to plant cells. These genes turn plant cells into factories producing chemicals used by the bacteria for nitrogen and energy. Infected cells form crown galls or root tumours, respectively. The Ti and Ri plasmids are thus endosymbionts of the bacteria, which are in turn endosymbionts (or parasites) of the infected plant.