Controlled-atmosphere (CA) storage may well prove to be the most significant technological innovation in the preservation of horticultural produce since the introduction of mechanical refrigeration. The process is widely used for the storage of apples in the United States, Canada, and England, and is becoming of increasing importance in other nations. There is strong interest in utilizing CA storage for other fruits and vegetables. In some cases, controlled atmospheres are being used in transportation units, such as freight cars, and in wholesale warehouses. The basic controlled-atmosphere process takes advantage of conventional refrigeration, but goes on to utilize rather precise regulation of gas levels in a sealed room to reduce further the respiration rate of the fruit. This generally means lowering oxygen levels and/or raising carbon dioxide levels. The lowered respiration rate leads to extended storage and shelf life (the period fruit will hold up on retail counters or in home refrigeration). Consequently, fruit can be held in good condition for a much longer period than is possible with conventional refrigeration alone. Formerly, for instance, preferred varieties of apples such as McIntosh could not be stored much past January; now they may be kept in fine condition until June or July, and could actually be held yearround if it were economically worthwhile. Special facilities are, of course, needed to reach and maintain the desired atmosphere. The basic requirement is a nearly airtight room; this calls for the use of metal or certain other linings and a sealed door. The apparatus for maintaining the required atmosphere ranges from fairly simple devices, which are manually controlled, to complex, semi-automatic generators. The latter are becoming increasingly important; in