In gymnosperms and woody dicots the roots and stems continue to increase in diameter forming secondary tissues (whereas in monocots and most herbaceous dicots  growth ceases with the maturation of the primary tissues ) This is called secondary growth and encompasses all lateral growth, a major component of woody plant tissues. It results from the activity of two lateral meristems:

1. Vascular cambium - gives rise to secondary xylem (wood) to the inside and secondary phloem to the outside

2. Cork cambium - gives rise to the periderm (bark) to the outside and phelloderm to the inside which replaces the epidermis, found only in woody plants