Growth is a permanent irreversible change brought about by increase in height, weight or volume. The three phases of growth are;
(a) Phase of cell division or cell formation: This region is located at the tip of shoot and root. It is represented by the apical meristem capable of rapid cell division. The cells are undifferentiated, with a thin cell wall made of cellulose, with an active protoplasm and prominent nucleus. This region is mainly concerned with cell division.
(b) Phase of cell elongation or cell enlargement:
This region lies next to the cell formation zone. The cells enlarge because of their elastic cell walls. Growth takes place during this stage either by apposition or intusucception. Cells are turgid.
(c) Phase of cell differentiation or cell maturation:
This represents the last region and differentiation based on functions is seen here. Secondary walls are laid down where some have additional deposits of lignin, Suberin and others lose their protoplast and become dead.
