A lenticel is an airy aggregation of cells within the structural surfaces of the stems, roots, and other parts of vascular plant. It functions as a pore, providing a medium for the direct exchange of gasses between the internal tissues and atmosphere, thereby bypassing the periderm, which would otherwise prevent this exchange of gases. The name lenticel, pronounced with a soft c, derives from its lenticular shape. The shape of lenticels is one of the characteristics used for tree identification.
Lenticel formation begins during the development of the first periderm. In the stem, they usually appear below a stoma or group of stomata. Lenticels are found as raised circular, oval, or elongated areas on stems and roots. As stems and roots mature lenticel development continues in the newly forming periderm found at the bottom of cracks in the bark.
Lenticels are also present on many fruits, quite noticeably on many apples and pears. On European pears, they can serve as an indicator of when to pick the fruit, as light lenticels on immature fruit darken and become brown. Certain bacterial and fungal infections can penetrate fruits through their lenticels, with susceptibility sometimes increasing with its age.