In 1907 a bacterium that caused plant tumors, "Agrobacterium tumefaciens", was discovered and in the early 1970s the tumor inducing agent was found to be a DNA plasmid called the Ti plasmid. By removing the genes in the plasmid which caused the tumour and adding in new genes researchers were able to infect plants with "A. tumefaciens" and let the bacteria insert their chosen DNA into the genomes of the plants.