What is hollow that absorbs water like a stone?

Water-absorbing stones are also used as water-absorbing stones, because after water is stored in the basin, it can be sucked up slowly. Weeds and moss can be planted on the stone, which is green and moist and is a good stone for making bonsai. The essence of water-absorbing stone is sand, which is brittle and absorbent. Water-absorbing stone is brittle and easy to shape because of mystery, and can be chiseled, drilled and carved into various shapes at will. There are many natural caves of water-absorbing stones, some of which are interconnected and breathable, and there are small caves such as pores, which are the main reasons for strong water absorption?