Each cell is cemented to its neighbor by a middle lamella and, consequently, plant cells cannot migrate from one site to another. Plant development is therefore orchestrated by patterns of cell division and enlargement, which are under hormonal regulation. Young, growing cells and metabolically active cells have only thin primary cell walls. When cell enlargement ceases, most plant cells deposit a secondary cell wall, between the primary wall and the plasma membrane, which is typically much thicker and stronger than the primary cell wall. Apical meristems , at the tips of the stem and roots, are the most active meristems in young plants.
Lateral branches emerge from axillary buds , which are apical meristems located at the stem nodes.
Lateral roots arise from the pericycle , an internal meristem tissue in roots. The development of the basic plant body and elongation of the plant is due to the activity of apical meristems and the pericycle and constitutes the primary growth. The formation of wood results from secondary growth. Plant Tissues . The epidermis is a dermal tissue.