Growth can be defined as an irreversible and permanent increase in size of an organ or its parts or even of an individual cell.
PHASES OF GROWTH IN PLANTS
The increased growth per unit time is termed as growth rate.
Plant growth and development are under the control of both intrinsic and extrinsic factors.
Intercellular intrinsic factors are the chemical substances, called plant growth regulators (PGR). There are diverse groups of PGRs in plants, principally belonging to 5 groups: auxins, gibberellins, cytokinins, abscsic acid and ethylene. These PGRs are synthesized in various parts of the plants.
Plant growth and development is also affected by external factors like light, temperature, nutrition, oxygen status, gravity, etc.
Flowering in some plants is induced only when exposed to certain duration of photoperiod. Depending on the nature of photoperiod requirements, the plants are called short day plants, long day plants and day-neutral plants. When plants are exposed to low temperature as to hasten flowering later in life, it is known as vernalization.