If the same phellogen functions from year to year, as in beech and oak, then the bark is smooth and consists only of tissue external to the phloem, mainly cork.
If the same phellogen functions from year to year, as in beech and oak, then the bark is smooth and consists only of tissue external to the phloem, mainly cork.
如在榉木或橡木中，相同的木栓形成层年复一年的活动，那么树皮是光滑的，并且仅形成韧皮部的外方组织，主要是木栓（软木）。