Regeneration is a specialized form of asexual reproduction; by regeneration some organisms can replace an injured or lost part, and many plants are capable of total regeneration—i.e., the formation of a whole individual from a single fragment such as a stem, root, leaf, or even a small slip from such an organ. F. C. Steward showed (1958) that single phloem cells from a carrot plant, when grown on an agar medium, would form a complete carrot plant. Among animals, the lower the form, the more capable it is of total regeneration; no vertebrates have this power, although clones of frogs (1962) and mammals (1996) have been produced in the laboratory from single somatic cells. Closely allied to regeneration is vegetative reproduction, the formation of new individuals by various parts of the organism not specialized for reproduction. In some plants structures that form on the leaves give rise to young plantlets. Rhizomes, bulbs, tubers, and stolons are other forms of vegetative reproduction.