Root apical meristem contains:
Root apical meristem contains highly organized niche with quiescent center comprising rarely dividing organizer cells surrounded by distinct stem cell initials for epidermis, lateral root cap, columella, cortex/endodermis common initial, and stele. Immediate daughters proliferate rapidly in meristematic zone, transit through elongation zone where vacuolar expansion dramatically increases length, then differentiate in maturation zone forming root hairs, Casparian strips, and mature xylem. Thus meristem integrates self-renewing stem cells maintained by WOX5, PLT, SHR/SCR signals and differentiating progeny enabling continuous growth while preserving precise radial and longitudinal patterning.
Ref: Gilbert, Developmental Biology, 12th ed., Chap 20 Plant Development: root meristem organization, stem cells plus differentiated cells.