phellem

Older phellem cells are dead, as is the case with woody stems.

Suberin is found in the phellem layer of the periderm (or cork).

Mature phellem cells have suberin in their walls to protect the stem from desiccation and pathogen attack.

Cork is an external, secondary tissue that is impermeable to water and gases, and is also called the phellem.

Together, the phellem (cork), phellogen (cork cambium) and phelloderm constitute the periderm.

In bark, phlobaphenes accumulate in the phellem layer of cork cambium, part of the suberin mixture.

Cells that grow inwards from the phellogen are termed phelloderm, and cells that develop outwards are termed phellem or cork (note similarity with vascular cambium).

Often a secondary covering called the periderm forms on small woody stems and many non woody plants, which is composed of cork (phellem), the cork cambium (phellogen), and the phelloderm.