The in vitro cultivation of plant tissues is generally carried out in a solid or semi-solid nutrient medium, using gelling agents. The type of gelling agent used can influence the growth of the tissue in culture. Both purity and cost of the gelling agent are important factors in any research or production operation.

Traditionally, agar is used, which is a polysaccharide extracted from seaweeds. The main differences among different agar-products are due to the impurities, their level and composition. Agar has been widely used since it has convenient gelling properties and stability during tissue culture. In all media used for in vitro culture of plants, agar is the major source of unknown variations.

Gums, such as gelan, produced by bacteria and commercialized under different names : Gel-Gro®, Gerlite® and Phyta-gel®, are polysaccharides that do not contain contaminating materials. Moreover, these products are used in lesser amount per liter than agar, to obtain the same consistency. They are added to the medium at approximately one fourth the concentration of agar. Furthermore, they appear more transparent.