There is a simple reason. There are two hormones. One is exogenous hormone, which you add to the culture medium, and the other is endogenous hormone, which is synthesized by plants themselves. At present, endogenous hormones such as IAA, 2,4-D, etc. (Remember these two) are known. If Bao Xiao mitogen is added first, the plant itself will have a certain amount of auxin and naturally divide and differentiate. (The above results are the results of research.

Auxin is beneficial to cell division before cytokinin, but it does not differentiate. In this case, it is easy to form polyploid cells, and cytokinin is beneficial to the formation of cell walls. Then, without cytokinin, plant nuclear division and cell wall formation will not be synchronized, leading to polyploidy.

Using two hormones at the same time can improve the frequency of differentiation, and the proportion of using two hormones at the same time affects the establishment of plant morphology to some extent. Generally speaking, a high proportion of auxin and cytokinin is beneficial to root differentiation and inhibits bud formation, while a low proportion is beneficial to bud differentiation and inhibits root formation, and a moderate proportion is beneficial to callus growth.