1. Phytohormones or plant growth regulators are internal factor that influence growth.
2. They inhibit, promote or modify the plant growth.
3. Plant hormones are organic substances produced naturally in plants and required in small amount.
4. Their place of production and site of the activity are different.
5. Auxins, gibberellins, cytokinins are growth promoters and ethylene, abscissic acid are growth inhibitors.
