Auxin is ubiquitous in lower and higher plants. Auxin is mainly concentrated in young and growing parts, such as the coleoptile of cereals, and its production has "self-promotion", such as the stem tip, young leaves, pollen and ovary of dicotyledonous plants, as well as the growing fruits and seeds. There is little content in aging organs. It is proved by coleoptile cutting that auxin in plants can only be transported from the upper end to the lower end, but not vice versa. This mode of transportation is called polar transportation, which can be carried out much faster than diffusion. However, the transport direction of auxin drugs applied from the outside depends on the application site and concentration. For example, the auxin absorbed by roots can rise to the tender part of the ground with transpiration flow. Low concentration of auxin can promote organ elongation. Thereby reducing transpiration and water loss. When it exceeds the optimum concentration, it will lead to the production of ethylene, which will reduce the promotion of growth and even turn into inhibition. Different organs have different responses to auxin. Roots are the most sensitive, buds are the second, and stems are the worst. The higher abscisic acid content in seeds is the main reason for seed dormancy. The main reason why auxin can promote cell elongation is that it can acidify the cell wall environment, increase the activity of hydrolase, relax the cell wall structure, increase the plasticity and increase the cell volume. Auxin can also promote the synthesis of RNA and protein, and promote cell division and differentiation. Auxin has duality, which can not only promote plant growth, but also inhibit plant growth. Low concentration auxin promotes plant growth, while high concentration auxin inhibits plant growth. 2,4-D has been used as a selective herbicide. Indoleacetic acid can be synthesized artificially. Synthetic auxin-like substances, such as indole propionic acid, indole butyric acid, naphthylacetic acid, 2,4 4- D, 4- iodophenoxyacetic acid, etc. Used in production, it can be used to prevent shedding, promote parthenocarpy, sparse flowers and fruits, take root in cuttings and prevent potato germination. Callus takes root easily; On the contrary, it is easy to germinate. The discovery of cytokinin began with the discovery of kinetin. It is transported downward or in both directions through phloem. From 65438 to 0955, F. Schugge of the United States accidentally discovered that adding DNA extracted from deteriorated herring sperm to the culture medium could promote the healthy growth of tobacco callus. It turns out that it contains an ingredient that can induce cell division, called kinetin. The first natural cytokinin is zeatin isolated from immature corn seeds by D.S. latham in 1964. Later, more than ten kinds of cytokinins were found in plants, including GA.