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(also cork cambium), a secondary formative tissue of plants, consisting of vacuolated thin-walled parenchyma cells. Phellogen cells, divided by septa growing parallel to the surface of the organ, deposit cork cells on the exterior and phelloderm cells in the interior. Phellogen and its derivatives make up the periderm.
In trunks of willow and apple, phellogen is deposited in the epidermis, while in elder and ash it is deposited in the subepidermal layer. It is deposited in the primary cortex in currant and larch and in the central cylinder in grape. In the roots of conifers and dicotyledons it is deposited in cells of the pericycle located around the conducting tissues, which retain their capacity to divide. A heavy deposit of phellogen in the secondary phloem of woody plants and the development of internal periderms cause the formation of crust.