Explanation
The apical meristem in roots is sub-terminal because it is covered by the root cap.
The root cap protects the delicate apical meristem as it grows through the soil, and the meristem is located just behind the cap. The apical meristem is responsible for the growth and development of the root, and it contains actively dividing cells that differentiate into different types of cells that make up the root. The tunica cells and corpus cells are layers of cells that make up the shoot apical meristem in the aboveground parts of plants and are not directly related to the sub-terminal position of the root apical meristem.
