In agriculture and gardening, seed saving (sometimes known as brown bagging) is the practice of saving seeds or other reproductive material (e.g. tubers) from vegetables, grain, herbs, and flowers for use from year to year for annuals and nuts, tree fruits, and berries for perennials and trees. This is the traditional way farms and gardens were maintained for the last 12,000 years (see first agricultural revolution). In recent decades, beginning in the latter part of the 20th century, there has been a major shift to purchasing seed annually from commercial seed suppliers. Much of the grassroots seed-saving activity today is the work of home gardeners. Method To be successful at seed saving, new skills need to be developed to ensure that desired characteristics are retained in the landraces of the plant variety. Important considerations are the separation distance needed from plants of the same species to ensure that cross-pollination with another variety does not occur, and the minimum number of plants to be grown which will preserve inherent genetic diversity. It is also necessary to recognize the preferred characteristics of the cultivar being grown so that plants that are not breeding true are selected against, and to understand the breeding of improvements to the cultivar. Diseases that are seed-borne must be recognized so that they can be eliminated. Seed storage methods must be good enough to maintain viability of the seed. Germination requirements must be known so that periodic tests can be made. Care must be taken, as training materials regarding seed production, cleaning, storage, and maintenance often focus on making landraces more uniform, distinct and stable (usually for commercial application) which can result in the loss of valuable adaptive traits unique to local varieties. Additionally, there is a matter of localized nature to be considered. In the upper northern hemisphere, and lower southern, one sees a seasonal change in terms of a cooler winter. Many plants go to seed and then go dormant. These seeds must hibernate until their respective spring season. Open pollination Open pollination is an important aspect of seed saving. Plants that reproduce through natural means tend to adapt to local conditions over time, and evolve as reliable performers, particularly in their localities, known as landraces or "folk varieties." Legality While saving seed and even exchanging seed with other farmers for biodiversity purposes has been a traditional practice, these practices have become illegal for the plant