In vascular plants, the root is the organ of a plant body that typically lies below the surface of the soil (compare with stem). However, this is not always the case, since a root can also be aerial (that is, growing above the ground) or aerating (that is, growing up above the ground or especially above water). On the other hand, a stem normally occurring below ground is not exceptional either (see rhizome). So, it is better to define root as a part of a plant body that bears no leaves, and therefore also lacks nodes. There are also important internal structural differences between stems and roots. The two major functions of roots are 1.) absorption of water and inorganic nutrients and 2.) anchoring the plant body to the ground. Roots also function in cytokinin synthesis, which supplies some of shoot needs. They often function in storage of food. The roots of most vascular plant species enter into symbiosis with certain fungi to form mycorrhizas, and a large range of other organisms including bacteria also closely associate with roots.