Interruptions in the phellem

Allow for gas exchange

The phellem of the periderm is practically impermeable for gases and water. Lenticels are interruptions in the phellem through which gas exchange occurs. The phellogen beneath lenticels is more active in cell division. It bends inward and produces filling tissue consisting of loosely arranged cells. Large intercellular spaces permit gas exchange. The cells of the filling tissue are easily torn apart by the pressure of the thickening stem. In many woody species, these cells have suberized walls. Lenticels are often initiated at the sites of stomata.

Shown here is a lenticel in cross-sectional view from the stem of elder (Sambucus sp.).