Figure 5-2 

 A growth chamber constructed at Colorado State University. Inside 

 dimensions are 4' 4'. Lights are 4' Sylvania VHO fluorescent lamps 

 (26 lamps) and 100 Watt incandescent lamps (9 lamps). Temperature 

 control is obtained by modulating the rate of flow of chilled brine 

 (ethylene glycol solution) or hot water through cooling or heating coils 

 at the back of the chamber. The control system is pneumatic (Johnson 

 Service Company). As the temperature exceeds the setting on the 

 thermoregulator, pressure increases so that the normally closed chilled 

 brine valve begins to open, admitting cooling fluid to the coils. As 

 temperature decreases below the setting, pressure decreases and the nor- 

 mally open hot water valve begins to open. In case of pressure failure, 

 hot water is no longer supplied to the chambers; upon overheating, 

 lights are automatically turned ofi" (except for a pilot lamp to protect 

 photoperiodism experiments), and a red light is turned on in the g -een- 

 house headhouse where it can readily be noticed. 



