Growth is defined as 'a permanent or irreversible increase in dry weight, mass or volume of a cell,
organ or organism'.
Plant growth takes place in three steps or phases cell division (meristematic), cell elongation and cell maturation.
(a) Cell division (Meristematic) phase : (i) It is also called formative phase, (ii) New cells are produced
by mitotic divisions of the pre-existing cells.
(iii) The meristematic cells have thin cellulose walls with abundant plasmodesmetal connections, dense protoplasm and conspicuous nuclei, (iv) In higher plants cell division occurs in meristems or growing points, (v) As the formation of new cells requires I intense biosynthetic activity, the rate of respiration the cells of formation phase is very high.
(b) Cell enlargement phase : (i) This phase lies just behind the growing points and is mainly
responsible for growth of plant parts, (ii) The newly formed cells, produced in formative phase undergo enlargement, (iii) The cell walls of the enlarging
of cell show plastic extension through enzymatic loosening of microfibrils and deposition of new
materials, (iv) The enlarging cell also develops a central vacuole. Rate of respiration is high but less
than that of the cells in the formative phase, (v) Thus, this phase is characterised by cell enlargement, new cell wall deposition and increased vacuolation. (vi) This phase is also called phase of cell elongation, (c) Cell maturation phase : (i) This phase occurs just behind the phase of elongation, (ii) The enlarged cells j develop into particular type of cells by undergoing
structural and physiological differentiation,
(iii) Hence, at this phase all the diverse tissue types observed in root or stem viz., epidermis, cortex,
vascular tissues etc., and cell are differentiated.