Formation of a new periderm cuts off ray contactwith the older periderm to outside.Because the energy supply is cut off, all tissueoutside the innermost periderm is dead.The names outer bark and rhytidome (落皮層 or 外樹皮) are both used to refer to all tissue outside the last-formed (functioning) periderm.Outer bark ranges from relatively thin (13-25 mm) in some species such as aspen to quite thick (0.3 m or more) in species such as Douglas-fi