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
Northern Hemisphere to draw air toward it in a counter-clockwise pattern. Hurricanes and tropical storms (massive low-pressure systems) spin counter-clockwise in the Northern Hemisphere. The shadow of a sundial moves clockwise in the Northern Hemisphere (opposite of the Southern Hemisphere). During the day, the Sun tends to rise to its maximum at a southerly position except between the Tropic of Cancer and the Equator, where the sun can be seen to the north, directly overhead, or to the south at noon dependent on the time of year. When viewed from the Northern Hemisphere, the Moon appears inverted compared to a view from