He explained that there are two ways of splicing foreign genes into a plant: by infecting it with agrobacterium, a pathogen whose modus operandi is to break into a plant cell’s nucleus and replace its DNA with some of its own, or by shooting it with a gene gun. For reasons not yet understood, the agrobacterium method seems to work best on broadleaf species such as the potato, the gene gun better on grasses, such as corn and wheat.