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GROWTH OF PLANTS 



Figure 118. Various plants grown under continuous sodium vapor light supplemented 

 by mercury vapor two hours per day. A, Tomato. B, Snapdragon. Left: artificial light; 

 right: greenhouse control. C, Gardenia. D, Tuberous rooted begonia. Left: greenhouse; 

 right: artificial light. E, Hyacinth. F, Geranium. Left: greenhouse control; center: 

 grown under continuous sodium vapor lamps supplemented by Mazda lamps, inter- 

 mittent illumination, 10 minutes on alternated with 20 minutes ofif; right: grown under 

 continuous 400-watt high intensity capillary mercury arc lamp. 



under this system of lights. The geranium that was injured by the continu- 

 ous illumination in the constant-light room did well under this combination 

 of lights. Later experiments have shown that a 150-watt Mazda lamp 

 burned intermittently can be substituted for the mercury vapor lamp. 



