Peridermgewebe

Peridermgewebe, often translated as periderm, is a complex tissue that forms the protective outer layer of the stems and roots of woody plants, and also of certain herbaceous plants. It serves as a replacement for the epidermis, which is typically shed as the plant grows in diameter. The periderm is a dynamic and multilayered structure composed of three main components: the phellogen (cork cambium), the phellem (cork), and the phelloderm.

The phellogen is a lateral meristem, meaning it is responsible for secondary growth in girth. It is a single layer of actively dividing cells that produces new cells both outwards and inwards. The cells produced on the outside differentiate into phellem, and those produced on the inside differentiate into phelloderm.

The phellem, commonly known as cork, consists of dead cells that are heavily suberized. Suberin is a waxy substance that makes the cork impermeable to water and gases, providing excellent protection against desiccation, mechanical injury, and pathogen invasion. The cork is the outermost layer of the periderm.

The phelloderm is formed inwards from the phellogen and consists of living parenchyma cells. These cells can store food and may play a role in the transport of water and nutrients.

Together, the phellogen, phellem, and phelloderm constitute the periderm. This tissue is crucial for the survival of woody plants, allowing them to withstand environmental stresses and grow larger over time. In many trees, the accumulation of periderm layers forms the bark. Lenticels, which are small pores or breaks in the periderm, facilitate gas exchange between the internal tissues and the atmosphere.