Plant Hormones: Phytohormones are chemical substances other than nutrients produced naturally in plants which regulate growth, development, differentiation and a number of physiological processes, e.g., auxin, gibberellins, abscisic acid, cytokinins. Hormone That Promotes Growth. Auxin/Gibberellin. Hormone That Inhibits Growth. Abscisic acid or ABA Hormone That Promotes Cell Division. Cytokinin. Hormone That Promotes Growth of a Tendril Around a Support. Auxin. (b) A-Pons Function: Relay centre, pneumotaxic area of respiratory centre. B-Medulla Function: Reflex centre, cardiac centre, respiratory centre. C-Cerebellum Function: Maintains equilibrium and coordinates muscular activities