Primary Root Structure
The seedling radicle ultimately becomes the primary root (tap root), which frequently develops side branches (lateral roots). In monocots the seedling radicle commonly dies at an early stage; the stem-borne (adventitious) roots of the mature plant originate from differentiated cells (Fig. 3.4). Adventitious roots can be branched or unbranched. Although roots can originate from various organs, their basic primary structure retains a characteristic root groundplan that is different from that of the stem. Each root possesses clearly-defined concentric tissue regions: dermal tissue (epidermis), ground tissue (cortex, including the endodermis) and central vascular tissue surrounded by a pericycle (Fig. 3.3).