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
Blue-winged warbler Blue-winged warbler The blue-winged warbler ("Vermivora cyanoptera") is a fairly common New World warbler, long and weighing . It breeds in eastern North America in southern Ontario and the eastern United States. Its range is extending northwards, where it is replacing the very closely related golden-winged warbler, "Vermivora chrysoptera". The common name "blue-winged warbler" refers to the bluish-gray color of the wings that contrast with the bright yellow body of the male. The name of the genus "Vermivora" means "worm-eating". The genus used to include nine other new world warblers but now includes only the golden-winged warbler and Bachman's warbler