298 



GROWTH OF PLANTS 



Figure 120. A, Red clover. The two pots of plants at the left were grown in the control 

 greenhouse, the two center with 6 hours of artificial light supplementing daylight and 

 with about ten times the normal concentration of CO2 (gantry crane greenhouse). The 

 two at right received the same illumination but no gas. Age from seed, 40 days. B, Three 

 of the same pots of clover shown in A with the 24-hour day plant added. The latter was 

 grown in the constant hght room with artificial light only. Age from seed, 69 days. 



The arrangement shown in Fig. 117 ilkiminates about 16 square feet of 

 bench surface at 3 cents a square foot per day. The mercury vapor lamp 

 used in this experiment differs from most mercury arcs in that it has a 

 continuous spectrum similar to sunlight over which is superimposed a 

 relatively strong bright line spectrum of mercury. The Mazda lamp, which 

 seems to balance the sodium vapor lamp about as well as the mercury arc 

 does, has dominant energy in the infrared and red-yellow, the blue-violet 

 being rather weak. These experiments indicate a generalization that we 

 shall have occasion to emphasize in connection with experiments to be 

 reported later. Green plants will not grow normally under monochromatic 



