Lateral meristems add thickness to woody plants, a process called secondary growth.
There are two lateral meristems: the vascular cambium and the cork cambium.
The vascular cambium adds layers of vascular tissue called secondary xylem = wood and secondary phloem.
The cork cambium replaces the epidermis with periderm, which is thicker and tougher.
An overview of primary and secondary growth
Shoot tip (shoot
and young leaves)
Primary growth in stems
Secondary growth in stems
The root tip is covered by a root cap, which protects the apical meristem as the root pushes through soil.
Growth occurs just behind the root tip, in three zones of cells:
Zone of cell division
Zone of elongation
Zone of maturation - differentiation.
Primary growth of a root
Zone of cell
The primary growth of roots produces the epidermis, ground tissue, and vascular tissue.
In most roots, the stele is a vascular cylinder.
The ground tissue fills the cortex, the region between the vascular cylinder and epidermis.
The innermost layer of the cortex is called the endodermis.
Root with xylem and phloem in the center
(typical of eudicots)
Root with parenchyma in the center (typical of
Organization of primary tissues
in young roots
Lateral roots arise from within the pericycle, the outermost cell layer in the vascular cylinder