külgmeristeemideks

Külgmeristeemideks are lateral meristematic tissues in plants responsible for secondary growth. Unlike apical meristems, which are located at the tips of roots and shoots and contribute to primary growth (lengthening), lateral meristems are found parallel to the stem or root axis and cause an increase in girth. The two main types of lateral meristems are the vascular cambium and the cork cambium.

The vascular cambium is a cylindrical layer of actively dividing cells located between the xylem and phloem. It produces secondary xylem (wood) towards the inside and secondary phloem (inner bark) towards the outside. This continuous production of secondary vascular tissues is what leads to the thickening of stems and roots in woody plants. The annual growth rings observed in tree trunks are a result of the seasonal activity of the vascular cambium.

The cork cambium, also known as the phellogen, is another lateral meristem found in the outer layers of stems and roots. It produces cork cells (phellem) towards the outside and, in some cases, phelloderm towards the inside. Cork cells are generally dead at maturity and suberized, providing protection against mechanical injury, desiccation, and pathogens. The formation of bark in trees is a consequence of the activity of the cork cambium and the tissues it produces. Together, these lateral meristems enable plants to increase in diameter, which is crucial for structural support and transport of water and nutrients in mature woody plants.