The cambium is a lateral meristem that produces xylem cells to one side and phloem cells to the other to form the vascular system.
Divisions in the vascular cambium provide lateral growth to a stem.
The initial cell is called a fusiform initial and its periclinal division creates cells on both sides of the cambium line.
In young stems, xylem and phloem appear in separated vascular bundles.
Cambium within the vascular bundle is called fascicular cambium, while the cambium between bundles is called interfasicular cambium.
With age, the vascular system and the cambium forms a complete ring within the stem.
Secondary growth occurs in woody plants as the stems continue to expand.
In addition to the vascular cambium, there is a cork cambium responsible for making bark or more correctly termed the periderm.
The periderm must continue to expand as the stem expands and the cork cambium is responsible for that axial growth.
The cork cambium is also called the phellogen.
It gives rise to cells that form the periderm, which is the term for the protective tissue that replaces the epidermis in a stem.
The periderm is made of three layers.
- The outer phellem (or cork) layer.
- The middle phellogen (cork cambium).
- And the inner phelloderm, which is living parenchyma cells formed to the inner side of the phellogen.