Q. CAN PLANTS GET CANCER? IF NOT, WHAT WOULD CAUSE A BULBOUS GROWTH ON A TREE?

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.