cross section: Pinus stem magnification: 100x

During the first year of growth the cutinized epidermis is replaced by protective growth of cork rich periderm. The outer periderm consists of layers of cork cells, the phellem, which produces waterproofing suberin. Cork cells are dead at maturity. Deep to the phellem is a living layer of cork cambium or phellogen and beneath that, layers of cork parenchyma or phelloderm. Many cells in the periderm contain dark staining tannins.

The cortex is divided into a thin outer hypodermis of lignified sclerenchyma cells and thicker inner cortex of thin walled parenchyma cells containing chloroplasts. Large resin ducts are surrounded by secretory parenchyma that produces resins and turpentines. Some cells enlarge into dark staining tyloses.

Conspicuous resin ducts are found in the cortex, primary and secondary xylem, but rarely the pith. The ducts are surrounded by secretory parenchyma that produces resins and many toxic terpenes including the turpentines. This antiseptic material solidifies when exposed to air, acting to seal wounds, to protect the plant from fungi, insect and bacterial infection and to discourage herbivores. Some secretory cells enlarge into dark staining tyloses that block the resin dusts.