Atlas of plant and animal histology

The periderm consists of three layers. The first layer is the cork cambium, or phellogen, characterized by cells that exhibit the standard traits of undifferentiated meristematic cells. They undergo mitotic division along tangential planes, generating multiple layers of cork (phellem) externally and phelloderm internally. Cork cells experience secondary wall thickening along with suberin accumulation, occasionally lignin. Subsequently, they perish and create a highly dense and impenetrable barrier to gases and water. In comparison, phelloderm cells are alive and lack suberin, distinguishing them from the cortical parenchyma due to their organized stacked arrangement

Lenticels are lenticular or circular structures protruding from the surface of the stems and roots. They have a pore and underlying parenchyma showing thin primary walls that leave intercellular spaces. Lenticels are formed together with the first periderm in those areas where the cork cambium is more active. As the epidermis grows thicker, new lenticels are produced. Lenticels function as passages for the gas interchange.

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