It is a method of conservation of tissue or plant under in vitro condition. There are two methods of In vitro conservation.
1. Short term conservation
2. Long term conservation (Cryopreservation)

Cryopreservation

The word cryo has been coined from a Greek word kryo meaning frost. The same principle is applied here too. The preservation is done in freezing conditions. This technique is utilized for germplasm conservation.
Following methods are utilized

1. On solid CO2 at -79 ° C
2. Low temperature Deep freeze at -80 °C
3. In vapor phase of N2 at - 150 °C
4. In liquid Nitrogen at -196 °C which is used for plant materials.