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
Mesoraphidiidae genera. Mesoraphidiidae are similar in overall appearance to modern snakefly species, having an elongated prothorax, giving a snake-like profile and from which the common name snakefly is derived. The family was likely tree-dwelling by nature, with larvae being active predators in trunks and branches. Female mesoraphidiids, where known and complete enough, have a long and densely annultated ovipositor which would have been used to lay eggs in crevices of bark. The family was restricted to the Northern Hemisphere, living in the warm temperate and paratropical forest belt that covered portions of Eurasia and North America. As currently described, Mesoraphidiidae contains