here is the link you can check detail about oak galls.
https://www.google.com.pk/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwji1oGH1evUAhUMpY8KHSuuDw0QjRwIBw&url=https%3A%2F%2Fwww.shutterstock.com%2Fsearch%2Foak-gall&psig=AFQjCNHorpUuAysZ9fEbgtnkcIe3DLptsQ&ust=1499121517793063