Plant breeders' rights (PBR), also known as plant variety rights (PVR), are rights granted to the breeder of a new variety of plant that give the breeder exclusive control over the propagating material (including seed, cuttings, divisions, tissue culture) and harvested material (cut flowers, fruit, foliage) of a new variety for a number of years. With these rights, the breeder can choose to become the exclusive marketer of the variety, or to license the variety to others. In order to qualify for these exclusive rights, a variety must be new, distinct, uniform, and stable. A variety is: new if it has not been commercialized for more than one year in the country of protection; distinct if it differs from all other known varieties by one or more important botanical characteristics, such as height, maturity, color, etc.; uniform if the plant characteristics are consistent from plant to plant within the variety; stable if the plant characteristics are genetically fixed and therefore remain the same from generation to generation, or after a cycle of reproduction in the case of hybrid varieties. The breeder must also give the variety an acceptable "denomination", which becomes its generic name and must be used by anyone who markets the variety. Typically, plant variety rights are granted by national offices after examination. Seed is submitted to the plant variety office, who grow it for one or more seasons, to check that it is distinct, stable, and uniform. If these tests are passed, exclusive rights are granted for a specified period (typically 20/25 years, or 25/30 years for trees and vines). Annual renewal fees are required to maintain the rights. Breeders can bring suit to enforce their rights and can recover damages for infringement. Plant breeders' rights contain exemptions from infringement that are not recognized under patent law. Commonly, there is an exemption for farm-saved seed. Farmers may store this production in their own bins for their own use as seed, but this does not necessarily extend to brown-bag sales of seed. Further sales for propagation purposes are not allowed without the written approval of the breeder. There is also a breeders' exemption (research exemption in the 1991 Act) that allows breeders to use protected varieties as sources of initial variation to create new varieties of plants (1978 Act), or for other experimental purposes (1991 Act). There is also a provision for compulsory licensing to assure public access