The growth of the tissues of living organisms outside the body in a suitable culture medium. Culture (or nutrient) media contain a mixture of nutrients either in solid form (e.g. in agar) or in liquid form (e.g. in physiological saline). Tissue culture is invaluable for gaining information about factors that control the growth and differentiation of cells, e.g. in testing drugs, cloning, and the production of stem cells. Culture of plant tissues such as callus has resulted in the regeneration of complete plants, enabling commercial propagation (e.g. of orchids) and—through culture of meristem tissues—the production of virus-free crop plants. See also explantation; micropropagation; tissue engineering.