Plant galls are formed from abnormal vegetative growth produced by a plant under the influence of an insect, mite, bacteria, fungus or nematode. It involves the intimate association of the plant host and the gall maker. Galls can be found on any part of the plant, but are most often observed as large, swollen growth on a leaf or branch. However, there are many other types that exist. The nature of gall formation was not discovered until recent times, even though galls have been written about since the days of the Roman Empire. Galls are now believed to be caused by powerful plant-growth-regulating chemicals or other stimuli produced by the gallmaker. It is well known that galls form as a result of cell multiplication in meristematic (growing) tissue. Gall formation cannot take place after a leaf or stem has stopped growing. Oak galls are induced by a number of different groups of insects as the abnormal growths composed of plant tissues for providing protection and food to the gall inducing insect. Mites are usually found in erineum galls, blister galls, and various types of pouch galls, often on the buds of leaves.