Meristeems

Meristems are specialized regions of undifferentiated plant cells that are capable of continuous division. These actively growing tissues are responsible for the plant's primary and secondary growth. Primary growth, which leads to an increase in length, occurs at the apical meristems located at the tips of roots and shoots. These apical meristems are responsible for producing new leaves and flowers, as well as extending the root system deeper into the soil.

Secondary growth, which results in an increase in girth or thickness, is facilitated by lateral meristems. The two main types of lateral meristems are the vascular cambium and the cork cambium. The vascular cambium produces secondary xylem (wood) and secondary phloem, increasing the diameter of stems and roots. The cork cambium, also known as the phellogen, produces the outer protective layer of bark.

Meristematic cells are typically small, isodiametric, and have thin primary cell walls. They possess dense cytoplasm and prominent nuclei. Their rapid rate of division allows plants to respond to environmental changes and develop complex structures. The activity of meristems is regulated by a variety of internal and external factors, including hormones and environmental cues like light and temperature.