Growth is influenced by a number of external and internal factors. These are environmental, physiological, nutritional and genetic. Growth in fact is the sum total of the interplay of all the metabolic activities. Some of these factors are-
Light, Temperature, Water supply and oxygen supply are the chief environmental factors that influence growth.
Light by itself has no influence on growth. In fact high intensities of light may even retard the growth of a plant. Plants grown in complete darkness however show etiolating i.e., yellowing of the leaves due to poor development of chlorophyll.
Absence of light, leads to elongation of internodes tenderness in stem and poor development of mechanical tissues. On the other hand, plants grown in the presence of light are strong statured. Light also helps in morphogenesis. Duration of light affects the flowering process and this is called photoperiodism
Growth is the final morphological expression of various metabolic activities taking place in the plant. Temperature influences all these metabolic activities and hence influences growth also. Generally a temperature range that is suitable for other metabolic activities is ideal for growth also. Though growth occurs in the range of 4°C – 45°C, optimum range is 28°C – 35°C. Very low temperature is injurious to the plant (cold injury), so also very high temperature. Temperature also influences the process of flowering (verbalization).
Adequate supply of water is necessary for all physiological activities including growth. Plants under water stress cannot grow properly. Oxygen supply: Proper supply of oxygen will ensure the process of growth by providing adequate energy to the dividing cells by way of respiration. It is possible that 02 may have some influence on the G1 stage of cell division.
Proper availability of nutrition, both organic and inorganic is necessary for growth. Plants under starvation have retarded growth. Supply of essential elements is necessary for the functioning of many enzymes which influence growth.
Growth pattern is controlled by the ratio of carbohydrates to nitrogenous compounds. A higher nitrogenous material in relation to carbohydrates is known to produce more of protoplasm, less mechanical tissues and strong vegetative growth. A higher amount of carbohydrates in relation to nitrogenous matter on the other hand favors the production of wall mate rial, mechanical tissues etc.
Genetic characters like the types of genes that an individual plant inherits has an enormous influence on growth. Proper growth takes place due to the interplay of genetic and environmental factors.
Studies on growth have revealed that certain chemicals synthesized by the plants themselves have a profound influence on growth. These are organic compounds synthesized in minute quantities but are very potent growth regulators. These are called Growth hormones (Phytohormones growth promoters).