A plant needs roots for anchoring itself to the ground and to absorb mineral salts and water from the soil. Most plants have their roots growing in the soil.
Roots regularly elongate at their tips and come in contact with new portions of the soil. Roots can be of two kinds, some plants have large, bulky roots called tap roots; some plants like grasses have fibrous roots. Fibrous roots protect soil from erosion.
There are some plants whose roots do not grow in the soil. Some tropical orchids that grow on trees have spongy roots.
Below Plant’s Root info from Wikipedia (Read More):-
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial (growing above the ground) or aerating (growing up above the ground or especially above water). Furthermore, 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 first root that comes from a plant is called the radicle. The two major functions of roots are 1) absorption of water and inorganic nutrients and 2) anchoring of the plant body to the ground. In response to the concentration of nutrients, roots also synthesise cytokinin, which acts as a signal as to how fast the shoots can grow. Roots often function in storage of food and nutrients. 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.
http://en.wikipedia.org/wiki/Plant_root
