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. The decreased water concentration is indicated by dark areas that emerge around the root system. In areas with insufficient water concentration the rootlets cease to grow before they have reached their potential full length.