When it comes to saving economic plant seeds, preserving seed stock is the most important aim. Saving seeds for later use was a necessity that was recognized by early humans. As agriculture advanced, man understood more and more about how to keep seeds alive and how to store them optimally.Farmers and seed firms have learned that keeping seeds for two or more years rather than one season is more cost-effective than doing so for one year to assure a consistent supply of plants for the following year. This method can be used to build up genetic reserves that will be valuable in the years following periods of low output. Most of the world's seeds are exchanged freely and come from a diverse range of plants including crops, flowers and forages, amongst others. Many of these seed lots won't be used again this year.