Plant hormones, also known as phytohormones, are chemical substances that regulate plant growth and development. Auxin (5 letters) is a type of plant hormone that promotes cell elongation and differentiation. It is involved in many aspects of plant growth and development, such as phototropism, apical dominance, and the formation of root and shoot systems. Abscisic acid (8 letters) is another type of plant hormone that regulates processes such as seed dormancy, leaf abscission, and fruit ripening. It is also involved in the regulation of stomatal closure and the response of plants to environmental stress.