vascular strand, pericycle and pith are formed by ?

dermatogen forms ?

Vascular strand, pericycle and pith are part of stele (the central region) are formed from PLEROME. It is the central core of primary meristem of a plant.
Dermatogen meristem gives rise to epidermis. In roots it also gives rise to root cap along with epidermis.
Periblem is inner to dermatogen which gives rise to cortex part.