Anatomy of a tree trunk.
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   Periderm consists of the cork cambium plus the layers of cork cells it
   produces.
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   Bark  consists  of tissues external to the vascular cambium, including
   secondary phloem and periderm.
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   The  older  layers  of secondary xylem (heartwood) no longer transport
   water and minerals, leaving that function to the outer sapwood.
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   In  temperate  regions,  the  vascular  cambium becomes dormant during
   winter. leaving annual rings.