cross section: One year Quercus stem magnification: 400x

Quercus is noted for rapid cork formation. By the end of the first year the underlying activities of the cork cambium have replaced the epidermal and outer cortical tissues with a protective layer of cork rich periderm. The outermost layer of periderm consists of layers of cork cells, the phellem, which produce the waterproofing substance suberin. Cork cells are dead at maturity.

Deep to the phellem is a layer of living cork cambium or phellogen and just beneath that layers of cork parenchyma or phelloderm. Many cells in the periderm contain dark staining tannins.

In certain areas, the cork cambium over produces cork cells, resulting in the formation of ridges and deep cracks in the periderm. These deep fissures, or lenticels, permit gas exchange with tissues under the periderm.

Deep to the periderm is a cortex of loosely packed parenchyma.

Due to meristematic activity the vascular bundles have expanded to form a cylinder consisting of a narrow outer ring of primary phloem, a middle single layered ring of vascular cambium and a deeper large ring of primary xylem. The phloem is overlaid by heavy continuous ring of sclerenchyma.