An abnormal localized swelling or outgrowth produced by a plant as a result of attack by a parasite. Galls are caused by bacteria, fungi, nematodes, insects, or mites or by a combination of these agents. *Crown gall
is a common gall produced as a result of bacterial infection. The root knots produced by nematodes of the genus Meloidogyne are another example. Galls caused by insects are very diverse and include the oak apple caused by the gall wasp Neuroterus lenticularis and the pincushion galls on roses caused by the gall wasp Rhodites rosae.