Roots are organized into primary roots and side-roots . The latter may develop a frequently branched and extensive root system. Among the prominent types of roots are the tap roots where the primary root is dominant while the side-roots are hardly developed at all. The primary root goes deep into the soil. Swollen roots that have developed into storage organs are called turnips .
Adventitious roots are roots that originate directly at the shoot.
Rhizomes and shoots that touch the soil are able to form adventive roots. Epiphytes do often develop air roots . The picture shows a two-dimensional model of a root seeking water in the soil during its development. The initial water distribution has been predetermined, forming an S-shaped zone of high concentration indicated by the light colour. The growing tips of the main root and rootlets absorb water that diffuses in the soil.