phelloderm. in old stems, the epidermal layer, cortex, and primary phloem become separated from the inner tissues by thicker formations of cork. due to the thickening cork layer, these cells die because they do not receive water and nutrients. this dead layer is the rough corky bark that forms around tree trunks...
, woody main stem or trunk. neither shrub nor tree is a single taxon (unit of biological classification ) but each include members of many plant taxa. examples of shrubs include the lilac , forsythia , and azalea . shrub is an imprecisely defined term. there are some "trees" that have two or more trunks...