The correct option is D All the above
During the secondary growth in dicot stem, some of the hypodermal cells or the outer cortical cells becomes meristematic and starts giving away new cells. This layer is known as cork cambium or phellogen. This phellogen cuts off cells both on its outer side and inner side. The cells cut off on the outer side are phellem or cork cells, and the sections that are cut off on the inner side are phelloderm or secondary cortex. Phellem, phellogen, and phelloderm collectively constitute periderm.