Phellem (Cork)

Phellem, commonly called cork, is the outermost component of the periderm - a protective tissue made of dead, non-living cells with walls impregnated with suberin (a waxy, waterproofing substance), cut off centrifugally (outward) by the phellogen. It replaces the epidermis in the older stems and roots of many seed plants, and is characterised by cells arranged in regular, compact tiers and rows with essentially no intercellular spaces between them - an arrangement that makes cork an efficient barrier against water loss and pathogen entry. That barrier is not completely unbroken, however: it is punctuated here and there by lenticels, raised pores that allow limited gas exchange to continue even after the epidermis has been replaced. A related but distinct cell type, phelloi …