Tree tissue. It protects the trunk against the elements, disease, animal attack and fire. It is perforated by a large number of fine breathing pores called lenticels, through which oxygen diffuses. Bark is continually replaced by a living layer of cells called the cork cambium or phellogen. The London plane ("Platanus × acerifolia") periodically sheds its bark in large flakes. Similarly, the bark of the silver birch ("Betula pendula") peels off in strips. As the tree's girth expands, newer layers of bark are larger in circumference, and the older layers develop fissures in many species. In some trees such as the
Pteryx Pteryx Pteryx is a genus of beetles that is typically found in northern bogs in the Northern Hemisphere. They belonging to the family Ptiliidae which is referred to as feather-winged beetles as the hindwings are narrow and feather-like. Like most of the rest of the family, "Pteryx" are very small and live in rotting vegetative matter. They prefer rotting wood and are generally found under the bark of rotting logs or stumps. The "Pteryx" are less than 1 mm in length. They are polymorphic, in that they frequently occur in two forms, a normal variety, and a neonate form that