Lenticel

A lenticel is a raised opening or pore that develops on the epidermis or, later, on the bark of a stem or root during secondary growth. It forms in a region where the phellogen becomes locally more active than in the surrounding tissue, producing a mass of loosely arranged, thin-walled parenchyma cells there instead of compact cork - this loosely packed patch is called the complementary tissue or filling tissue, and it is what keeps the lenticel from sealing over the way the rest of the cork layer does. Functionally, lenticels are the periderm's answer to the stomata it has replaced: they allow the living tissues beneath an otherwise near-impermeable corky bark to keep exchanging gases with the at …