Plant tissue culture has become popular among horticulturists, plant breeders and industrialists because of its varied practical applications. It is also being applied to study basic aspects of plant growth and development. The discovery of the first cytokinin (kinetin) is based on plant tissue culture research. Plant tissue culture relies on the fact that many plant cells have the ability to regenerate a whole plant (totipotency). Single cells, plant cells without cell walls (protoplasts), pieces of leaves, stems or roots can often be used to generate a new plant on culture media given the required nutrients and plant hormones. Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues or organs under sterile conditions on a nutrient culture medium of known composition. Plant tissue culture is widely used to produce clones of a plant in a method known as micropropagation.