Seed balls, also known as earth balls or nendo dango (Japanese: 粘土団子), consist of a variety of different seeds rolled within a ball of clay, preferably volcanic pyroclastic red clay. Various additives may be included, such as humus or compost. These are placed around the seeds, at the center of the ball, to provide microbial inoculants. Cotton-fibres or liquefied paper are sometimes mixed into the clay in order to strengthen it, or liquefied paper mash coated on the outside to further protect the clay ball during sowing by throwing, or in particularly harsh habitats.