The presence of casparian strips on cork cells, and the structure and the development of the lattice-work phellem are described. Three to four subsequent periderms are formed during a growing season in the young branch. Most of these arc parallel to each other. Each periderm is composed of layers of radially elongated thin-wall non-suberized *cork ray cells', alternating radially with a flattened casparian strip bearing suberized cells. The significance of the casparian strip in the cork of the stem is also described.