How roots perceive and respond to gravity.

During their growth and development, plants exhibit several types of tropisms and movements (e.g., epinasty, circumnutation, gravitropism, phototropism). The tropism first exhibited by most plants in the positive gravitropism characteristic of their newly emerged primary roots. Indeed, these roots must quickly "locate" water and minerals in the soil so as to insure survival of the plant. Thus, it is not surprising that the evolutionary process has produced an elegant system for graviperception and gravitropism by plant roots.