The cork cambium is the main tissue that is responsible for the formation of wood. The girth of the stem increases due to increased activity of the vascular cambium. As the girth keeps increasing the outer cortical layers starts rupturing. So, cork cambium produces new layers that replace the damaged or ruptured layers. Cork cambium is also called phellogen. The cork cambium has another name that is stellar cambium. Phellogen is thick and has two layers. The outer one forms the cork and the inner one forms the secondary cortex. The cells of cork are compactly arranged and in the beginning, they have thin cellulose cell walls. When they mature the living part is replaced by the non-living part which is the formation of wood material. The cell walls of the cork become thick by the deposition of suberin.