What distinguishes the periderm from the epidermis in woody plants?

The periderm is a protective layer that replaces the epidermis in woody plants as they grow and undergo secondary thickening. One of the most distinguishing features of the periderm is the presence of cork cells, which are specialized cells that make up a significant portion of this layer. Cork cells are known for their ability to form a barrier to protect the plant from environmental threats, such as pathogens and moisture loss, and their walls are impregnated with suberin, making them particularly durable and resistant to water.

In contrast to the epidermis, which is typically thin and may contain photosynthetic chloroplasts, the periderm is significantly thicker due to the accumulation of cork tissue. This structural difference is vital for the plant's protection as it matures. While the periderm does facilitate some gas exchange through structures called lenticels, its primary function is to act as a barrier, further distinguishing it from the epidermis, which is primarily involved in initial plant protection and water retention.

The presence of cork cells in the periderm also contributes to its insulating properties, helping woody plants to endure varying environmental conditions.