1) is mainly composed of single cells and small cell clusters;

2) Cells have rich ability of growth and division and rapid proliferation;

3) Most cells should have the characteristics of meristem in morphology, and most of them have the same diameter, large nuclear-cytoplasmic ratio, dense cytoplasm and low aneuploidy. To construct such a floating culture system in the county, it is necessary to have a good initial culture-rapid proliferation of loose callus. Then, it is realized through the selection of culture medium components and culture conditions and repeated subculture. After long-term subculture, the chromosomes of floating culture cells in county towns often mutate. The regenerative capacity of cells also tends to decline gradually. However, for a large number of cultures aimed at producing useful metabolic characteristics, this reduction in regenerative capacity does not necessarily have an adverse effect.