Modern advances in genetics have allowed humans to more directly alter plants genetics. In 1970 Hamilton Smith's lab discovered restriction enzymes that allowed DNA to be cut at specific places, enabling scientists to isolate genes from an organism's genome. DNA ligases, that join broken DNA together, had been discovered earlier in 1967 and by combining the two technologies it was possible to "cut and paste" DNA sequences and create recombinant DNA. Plasmids, discovered in 1952, became important tools for transferring information between cells and replicating DNA sequences. 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 that caused the tumor and adding in novel genes researchers were able to infect plants with "A. tumefaciens" and let the bacteria insert their chosen DNA sequence into the genomes of the plants. As not all plant cells were susceptible to infection by "A. tumefaciens" other methods were developed, including electroporation, micro-injection and particle bombardment with a gene gun (invented in 1987). In the 1980s techniques were developed to introduce isolated chloroplasts back into a plant cell that had its cell wall removed. With the introduction of the gene gun in 1987 it became possible to integrate foreign genes into a chloroplast. Genetic transformation has become very efficient in some model organisms. In 2008 genetically modified seeds were produced in "Arabidopsis thaliana" by simply dipping the flowers in an "Agrobacterium" solution. In 2013 CRISPR was first used to target modification of plant genomes.