Plant Growth and Development — BIOLOGY STD 11 Science — Question

Apical, lateral and intercalary are the special regions, where growth is localised in plants. At the apex of every root and shoot apical meristems are present which are responsible for the elongation of plant along their axis. This is known as primary growth of the plant.
The lateral meristems, vascular cambium and cork cambium appear later in life in dicotyledonous plants and gymnosperms and are responsible for the increase in the girth of the stem.
This increase in girth is known as secondary growth of the plant.

Diagrammatic representation if locations of root apical meristem, shoot apical meristem and vascular cambium. Arrows exhibit the direction of growth of cells and organ.