Formative phase - It is also called cell formation or cell division. New cells are produced by mitotic division of the pre existing cells.
Phase of enlargement - The newly formed cells produced in the formative phase undergo enlargement cells wall of the enlarging cells show plastic extension through enzymatic loosing of microfibrils and deposition of new material.
Cell differentiation or (maturation phase) - Cell becomes specialised according to their function. Permanent changes take place in this phase. Secondary cell walls are formed.