8 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. ^J 



meter, thence to a long spiral coil in the humidity-control tank at 

 temperature T-. Excess humidity produced by the transpiration of 

 the plants condenses in this coil and may be removed from the con- 



FiG. 3. — Detailed diagram of control systems. 



densation bulb by a stopcock. As it passes through the spiral in the 

 humidity-control tank the air is driven by a fan through the spiral 

 in the upper control tank, where it is brought back to temperature TS 

 and so returned by means of the manifold to the chambers. The 

 proper humidity is of course maintained by suitable adjustment of 



