When a seed germinates, the radicle of the embryo comes out. The radicle of the embryo develops into first root or primary root. The primary root gives rise to other roots called secondary roots or lateral roots. Finally lateral roots give rise to tertiary roots. When the primary root alone continues to grow, the type of root system formed is known as tap root system. Here, the primary root develops from the radicle of the embryo and remains as the main root throughout the life of the plant and grows straight downwards in the soil. The best example of this type are dicot plants.