Kuoriparenkymä

Kuoriparenkymä refers to the phellogen, a layer of meristematic cells found in the outer bark of woody plants. This actively dividing tissue is responsible for producing secondary phloem towards the inside and periderm towards the outside. The periderm, which replaces the epidermis as the plant grows, consists of three layers: the phellem (cork) on the outside, the phellogen in the middle, and the phelloderm on the inside. Together, these layers form the protective outer bark of trees and shrubs.

The primary function of kuoriparenkymä is to generate new bark tissue, which serves as a barrier against mechanical injury, desiccation, and pathogen invasion. As the plant stem or root increases in diameter, the outer tissues, including the original epidermis, are stretched and eventually rupture. The continuous production of periderm by the kuoriparenkymä ensures that the plant remains protected by a living, functional bark throughout its life. The thickness and composition of the periderm can vary significantly between species, contributing to the diverse textures and appearances of tree bark. In some plants, the phellogen may be replaced by new meristematic layers deeper within the stem as the bark expands.