Storage of cultures in liquid nitrogen (LN2) is superior but expensive. It is the best long term culture storage method because mycelial growth is completely suspended at -196C. This method maintains a very stable mother culture for many years. Only the highest quality mycelial cultures are selected for long term storage -- a culture's qualities will not improve with storage. Unfortunately it is also the most expensive. Initial equipment costs are high and liquid nitrogen is a continual monthly expense. The liquid nitrogen storage unit requires constant monitoring of the liquid nitrogen level in the chamber. The basic method is to fill a cryotube (special plastic tube designed for use in LN2 ) with a cryoprotectant and then to submerge a few mycelial plugs or spawn grains into the liquid. Then the filled cryotube is placed in a divided box or cane, then into rack and finally housed in the cryostorage unit. The purpose of the cryoprotectant it to protect the mushroom cells from damage during the freezing and thawing cycles.