In a plant organ which is covered by periderm and in which the stomata are absent, some gaseous exchange still takes place through
aerenchyma
trichornes
pneumatophores
lenticels.
D.
lenticels.
Due to continued formation of secondary tissues in the older stem and roots however the epidermis gets stressed and ultimately tends to rupture and followed by death of epidermal cells and outer tissues, and a new protective layer is developed called periderm.
Structurally it consists of three parts Phellogen or Cork cambium, phellem or cork and phelloderm. Usually in the periderm of most plants, certain areas with loosely arranged cells have been found, which possess more or less raised and corky spots where the underneath tissues break through the epidermis. Such areas are universally found in the stems of woody plants. These broken areas are called lenticels, which perform the function of exchange of gases in the absence of stomata.
