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An institution where plant material, in danger either of becoming extinct in the wild or of being lost from cultivation, is stored in a viable condition. In many such centres the emphasis is on maintaining collections of plants of demonstrated or potential use to man, e.g. crop varieties containing useful genes that have been superseded by improved cultivars. Normally seed material is dried down to about 4% moisture and stored at around 0°C preferably in hermetically sealed containers. For many seeds such conditions will maintain viability for 10-20 years and longer. The seeds of some species, including many tropical plants, cannot be dried without killing them and yet have a limited lifespan in the hydrated state. Such material must be maintained in the growing condition. The problems of space and maintenance that this entails may in some instances be overcome by tissue-culture methods. All material must periodically be sown to check viability and multiply seedstock. Pollen may also be stored in gene banks though generally the longevity of pollen is less than that of seeds. See also genetic erosion, genetic resources.
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