Phellogen, also known as cork cambium, is a type of lateral meristem found in the stems and roots of many plants. It is responsible for producing the outer protective layer of bark, which is primarily composed of cork cells. This layer helps to protect the plant from environmental damage and water loss. The phellogen forms a continuous layer of cells that divides to produce cork cells on the outside and phelloderm cells on the inside. This process contributes to the secondary growth of plants, allowing them to increase in girth over time, which is essential for the overall health and stability of woody plants.