meristems

Meristems are plant tissues composed of undifferentiated, actively dividing cells that drive growth and development. The cells in meristems retain the ability to proliferate and to give rise to specialized tissues, enabling the continual formation of new organs throughout the plant’s life.

Meristematic tissue occurs in specific regions: apical meristems at the tips of shoots and roots for primary growth; lateral meristems, including the vascular cambium and cork cambium, for secondary growth; and intercalary meristems, common in many monocots, at leaf bases or internodes to add length.

During primary growth, three primary meristems form from initial cells: protoderm, which gives rise to the epidermis; ground meristem, which forms the cortex and pith; and procambium, which differentiates into the vascular tissues (xylem and phloem).

Lateral meristems produce tissues that thicken the plant: the vascular cambium generates secondary xylem and secondary phloem, while the cork cambium produces the protective periderm (cork).

Meristematic cells are small, with dense cytoplasm, large nuclei, thin primary cell walls, and minimal vacuolation. They divide by mitosis and are often arranged in clusters or longitudinal files. Growth is regulated by hormones such as auxins, cytokinins, and gibberellins, as well as genetic controls responsive to environmental cues.

Meristems enable lifelong growth, tissue repair, and regeneration. They are central to propagation and biotechnology, where meristem culture can produce clonal plants and recover tissues from damaged material.