A breath of fresh air
Most of the tree's gas exchange is done through its leaves. The trunk and branches also need to absorb oxygen and release carbon dioxide. Whoops! The bark, that wonderful invention that does such a great job of protecting the trunk and branches from the tree's hostile environment, is impermeable and actually blocks gas exchange.
That's where the lenticels (Lens-shaped, biconvex spot on the surface of a plant, which serves as a pore.) come in. These windows on the outside world make it possible to confine the gas exchange needed for the trunk and branches to a small, well defined area without interfering with the bark's ability to protect the tree.
