Growth in plants occurs by cell division and cell enlargement, followed by cell differentiation.
Growth in plants is generally limited to regions of growing points known as meristems. The two important growing points present in the root apex and stem apex are called apical meristems and growth due to them is known as primary growth. The formation of tissues of a plant, the increase in the length of the plant and the differentiation of various appendages are due to the primary growth.
In certain kinds of plants e.g., bamboo, mint, increase in length is also due to intercalary meristems. These are actually a part of the apical meristems which get separated from the apex by the intervening permanent tissues. These meristems are of a temporary nature. A third type of growing point is known as the lateral meristems, which is responsible for the thickness of the plant in girth. This is called secondary growth. Here meristematic cells, in the form of cambium are present in the vascular bundles of root and stem, thus increasing their thickness.