ABSTRACT
Galls caused by mites are acarocecidia, by nematodes are nematocecidia, by fungi are mycocecidia, and by bacteria are baeteriocecidia. Oak galls produced by cynipids are the best known and, because they are rich in tannin, the most exploited. Galls were once considered as harmful to the plants, but now the tendency is to consider the gall as advantageous since it protects the plant against possibly even greater damage, the complete necrosis of the parasitized tissues. The formation of a gall, which is an hypertrophy or dysplasy of a tissue, restricts the damage not only to a certain region of the plant, but also to a particular time in the plant life cycle. The histological structure of galls is variable, sometimes rather complex. The chemical composition of the galls has been well studied and several of them are very rich in tannins and in anthocyanins which give them their colors.
