What is a gall?
Abnormal growth/swelling in a plant. Can be induced by infection from bacteria or fungi, or by attack from mites, nematodes or insects. Can form on any of a plant’s organs. Some indiciated a type of disease, while others cause no harm to host. Some are beneficial (nodules in the legume family fix N2). Many galls are caused by cynipid wasps that lay eggs in plant tissues. The CA gall-fly produces large-diameter oak apples and many other species associate with the gall.