If human body have hormones, same true with plants and this plant hormones called auxin. It is a substance naturally produced in actively growing parts of plants that regulate many aspects of plant...
Auxins are a class of plant growth substance (often called phytohormone or plant hormone). Auxins play an essential role in coordination of many growth and behavioral processes in the plant life...
Auxin were the first plant hormones discovered. Charles Darwin was one of the first pioneers and wrote a book called The Power of Movement in Plants - 1880