Plants do not have nervous system. In plants control and co-ordination takes place by chemical substances called plant hormones or phytohormones. Plants secrete hormones such as Auxin, Gibberlins, Cytokinins, Absicisic acid, Ethylene. These hormones control growth, reproduction, germination, dormancy, ripening of fruits etc. Environmental factors such as light, temperature, humidity, gravity etc. acts as stimuli to the plants which sometimes may enhance or inhibit various activities of the plant body. The action of the hormones highly depends upon these environmental factors.