Lenticel

Lenticels are small, often lens-shaped porous structures on the bark surface of trees that facilitate gas exchange between the living tissues inside the trunk and the outside atmosphere. They appear as raised bumps, horizontal lines, or corky patches on bark and are particularly visible on young, smooth-barked trees like birch and cherry, where they form distinctive horizontal markings.

Living cells within the trunk and branches require oxygen for respiration and release carbon dioxide as a waste product. Since the bark's primary function is protection, it is largely impermeable to gases. Lenticels provide the necessary ventilation, containing loosely packed cells with abundant air spaces that allow gases to diffuse in and out. They develop from the same cork cambium that produces bark.

While lenticels serve an essential function, they can also serve as entry points for pathogens. Some bacterial and fungal diseases gain access to internal tissues through lenticels, particularly when bark surfaces remain wet for extended periods. Fire blight bacteria, for example, can enter through lenticels during warm, humid weather. This is one reason why maintaining good air circulation around trees helps prevent disease. Lenticels can also become waterlogged during flooding, which impairs oxygen exchange and contributes to flood damage in trees.