Nutrient Media - Virtually all tissue culture media are synthetic or chemically defined; only a few of them use complex organics, e.g., potato extract, as their normal constituents. A synthetic medium consists of only chemically defined compounds. A variety of recipes have been developed since none of them is suitable for either all plant species or for every purpose. Most of these recipes have been elaborated from those of White (itself evolved from a medium for algae) and Gautheret (based on Knop's salt solution). The composition of White, MS and B5 (the last two are the most commonly used) media.