Galls are structures budded out from stems, leaves, or other pats of plants. Galls are made by insects for the protection of their young or immature larvae. Pictured is the oak apple gall, about two thirds its natural size. Also pictured is the young root of oak bearing galls.
Nicholson, George The Illustrated Dictionary of Gardening, Div. VI (London, England: L. Upcott Gill, 1884)