-in most dicots and gymnosperm, secondary thickness growth also occurs in the root

-cambium forms from the parenchyma between xylem and phloem and partly out of the pericycle

-as in shoots, it produces secondary phloem (to the outside) and secondary xylem (to the inside)

-the pericycle also becomes a cork cambium forming a periderm (in shoots it is the layer below the epidermis)

-thus, all layers outside the periderm (cortex and rhizodermis) die and are shed