In plant tissue culture, the formation of typical callus from explants usually goes through three stages: initiation, division and formation. Start-up refers to the period when cells are ready to divide. Exogenous plant growth hormone has a good effect on inducing cell division. Commonly used are naphthylacetic acid, indoleacetic acid and cytokinin. Generally, the ratio of cytokinin to auxin is 1: 1 to induce callus formation of plant materials. Mitosis refers to the dedifferentiation process of explant cells after the induction, continuous division and proliferation of daughter cells. Mitotic callus is characterized by rapid cell division, loose structure and light and transparent color. Differentiation refers to a series of morphological and physiological changes of cells at the end of division, thus producing cells with different shapes and functions in callus. These cell types include parenchyma cells, meristem cells, pigment cells, fibroblasts and so on. After a series of changes, such as start-up, division and differentiation, explant cells form callus with disordered structure. If we continue to cultivate callus on the original medium, it will stop growing, even aging, blackening and death because of insufficient nutrition or the accumulation of toxic metabolites in the medium. If the callus continues to grow and proliferate, it must be divided into small pieces regularly (2-4 weeks) and inoculated on fresh culture medium, so that the callus can maintain vigorous growth for a long time.