Peeling bark on a London Plane tree, Platanus x hispanica. Tree bark has areas of thin walled cells called pores that allow the exchange of oxygen...

Peeling bark on a London Plane tree, Platanus x hispanica. Tree bark has areas of thin walled cells called pores that allow the exchange of oxygen and carbon dioxide. Pollutants in cities block the pores. However, the Plane, a popular tree in city streets, remains healthy by regularly shedding its bark which renews the pore structures.