A gall is an area of abnormal plant growth, usually induced by a virus or insect, such as a gall wasp. There are around 90 gall wasps in Britain, 42 of these are associated with oaks. Each species induces a gall of a constant shape and form for the purpose of shelter and food. Oak marble galls look like marbles attached to twigs at the base of leaves. They turn brown as they mature and small round holes where the wasp has emerged are often seen. The Oak marble gall wasp was introduced in the 1840s from the Middle East as the galls they produce are used to make inks and dyes. Before this time, the galls were imported. The galls were crushed and mixed with water, iron sulphate and gum arabic. The resulting ink was the main medium for writing in the western world. A huge number of important historical documents are written and dawn with iron gall ink including the Magna Carta, Leonardo da Vinci’s notebooks and the American Declaration of Independence. This process was described by George McGavin when filming the BBC’s ‘Oak Tree: Natures Greatest Survivor’, which featured a parkland oak at Wytham.