Crown gall is a plant tumor incited on dicotyledonous plants by infection with a bacterium, Agrobacterium tumefaciens. During this process, a portion of a large plasmid contained in the bacterial cell is transferred and incorporated into the genome of the host plant cell. The transferred plasmid DNA, the T-DNA, carries information for products that either control or code for the synthesis of plant hormones. The increased level of phytohormones causes the transformed cells to escape from host control mechanisms and proliferate limitlessly, thus causing a tumor. The T-DNA also contains...