In trunks, periderm becomes replaced with rhytidome

In trunks of many woody plants the smooth periderm is separated from underlying layers by subsequent periderm. It is replaced with age by a cracked rhytidome (outer bark) consisting of several sequential periderms (layers of cork), and dead secondary phloem tissues between them as seen here for locust (Robinia sp.) stem. The accumulated outer bark therefore consists of alternating dead layers of secondary phloem and periderm with the oldest on the outside and the youngest on the inside, next to the living inner bark.