Can Plants Get Cancer? - NYTimes.com A. "Plants don't get cancer like animals do," said Susan K. Pell, director of science at the Brooklyn Botanic Garden, "and the tumors they do get do not metastasize because plant cells don't move around." Rather, they are held in place by cell walls. Plant tumors - aggregates of cells that have multiplied excessively - are usually caused by a bacterium, virus or fungus, or may develop as a result of structural damage, Dr. Pell said. "The bacterium Agrobacterium tumefaciens is one of the most common culprits in plant tumors and is the cause of crown gall," she said. The resulting growths are visible on trees in Brooklyn and elsewhere. Dr. Pell listed fungal infections like black knot, caused by Dibotryon morbosum, and azalea knot, caused by Exobasidium vaccinii, among other common plant tumors. Excess plant cell production in the form of galls sometimes benefits future generations of insects, Dr. Pell said. Wasp galls are perhaps the most frequently encountered of this type; the gall wasps Callirhytis cornigera and C. quercuspunctata affect oak trees. "These wasps lay eggs in new tissue that is still growing," Dr. Pell said, "and the plants produce excess tissue around the egg that ultimately both protects and feeds the insect larvae." Not much is known about the biology of the process, she said, but it is likely that chemicals, released either when the eggs are laid or in early development stages, interfere with how the plant regulates its growth.