Under the protective outer bark lies another layer of protection, the phellogen.
2.
In some species, like ash, old and new segments of phellogen become attached through intertwined fibers, resulting in a characteristic furrowed appearance.
3.
Woody dicots and many nonwoody dicots have secondary growth originating from their lateral or secondary meristems : the vascular cambium and the cork cambium or phellogen.
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