AP BIOLOGY

Detailed explanation-1: -Periderm is the corky outer layer of a plant stem formed in secondary thickening or as a response to injury or infection.

Detailed explanation-2: -The thickening of the stem that occurs in secondary growth is due to the formation of secondary phloem and secondary xylem by the vascular cambium, plus the action of cork cambium, which forms the tough outermost layer of the stem.

Detailed explanation-3: -The phellem, or cork, forms a series of cell layers at the outermost level of the periderm and is derived from the underlying meristematic phellogen layer (cork cambium).

Detailed explanation-4: -The lateral meristem tissues are responsible for the secondary growth of plants. The secondary growth of plants increase in stem thickness and it is due to the activity of the lateral meristems, which are absent in herbs or herbaceous plants.

Detailed explanation-5: -The cork cambium or pericambium or Phellogen initially forms from the parenchyma cells in the cortex and at times in the primary phloem. It produces new dermal tissues which gradually replaces the epidermis which is formed by the protoderm.