Figure 1. Examples of suberized cork tissues. The outer cork cells of the gymnosperm bark pictured at left represent the most abundant form of suberized cork in above-ground plants. The potato tuber, on the right, has a highly suberized periderm that is only five to six cell layers thick, but helps this storage organ maintain a high water content, even with prolonged storage. In the centre, a champagne cork illustrates one of the major industrial uses for suberized cork tissues.

Figure 2. Schematic diagram of a typical wood stem periderm. The phellogen is evident as a single continuous layer of rectangular, radially flattened cells. Note the position of the phellogen relative to the vascular cambium. Cells to the outside of the phellogen become suberized and form the phellem, or cork. Cells to the inside of the phellogen form the phelloderm, a segment of living parenchyma cells. The common term ‘bark’ refers to all the tissues outside of the vascular cambium, including both the phloem and periderm.

Figure 3. Electron micrograph of a suberized potato tuber cell wall. The picture is of a potato tuber cell that has been induced to suberize by wounding. Notice the multilamellar bands (arrow) between the cell wall and the plasma membrane. Bar, 0.5 m.

Figure 4. The chemical components of ‘suberin’. The major aliphatic components are the long-chain (i.e. C₁₆–C₃₂) fatty acids, alcohols, -hydroxyalkanoic acids and ,-dioic acids and glycerol. The dioic acids are considered diagnostic for suberized tissues. Minor components include 9,10-epoxy-18-hydroxy- and 9,10,18-trihydroxy-octadecanoic acids as well as 9,10-epoxy- and 9,10-dihydroxy-1,18-octadecandioic acids. For the aliphatics, only the C₁₈ octadecanes are shown. The aromatic components include the hydroxycinnamic acids, hydroxycinnamoyl amides and monolignols. Hydroxycinnamic acids can either be esterified to the aliphatic components, either directly or through glycerol, or covalently crosslinked to each other via C–C and C–O–C bonds as well as to other aromatic components and cell wall polysaccharides.