Plate 6. — Control chamber 5 feet by 2% feet, employed for growing 

 plants under specified conditions of light (artificial), temperature and humid- 

 ity. The apparatus is air conditioned with the aid of a refrigerator unit of 

 large capacity. In the experiment illustrated above fluorescent lights form 

 the source of illumination. In earlier investigations with young wheat plants 

 Mazda lamps were employed. Control of the root environment is gained by 

 furnishing to the roots the desired nutrient solution. Air movement is gov- 

 erned but measures for working with diffei'ent concentrations of CO2 in the 

 atmosphere have not yet been developed. Two chambers are at present avail- 

 able. (This illustration provided by K. A. Grossenbacher) . 



