12 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 97 



appears to be a general decrease in dry weight efficiency with illumi- 

 nation containing less of the shorter wave lengths found in the 

 mercury lamp. 



DISCUSSION 



Plants have been grown by Harvey (1922), Hendricks and Harvey 

 (1924), and others under Mazda lamps. Davis and Hoagland (1928), 

 Arthur, Guthrie and Newell (1930), Garner and AUard (1931), 

 Steinberg and Garner (1936), and others have conducted numerous 

 experiments in which good growth was obtained with Mazda lamps 

 for various lengths of daily light and dark periods. Many other in- 

 vestigators both in Europe and in this country have shown that plants 

 may be grown in artificial light whose wave-length distribution is 

 continuous from blue-violet to red. Other investigators have de- 

 termined the growth of plants in different portions of the spectrum. 

 Here it was necessary to use glass or liquid filters. Others, like 

 Roodenburg (1932), have used gaseous discharge lamps such as 

 neon. Most of these experiments indicate the necessity of the full 

 visible spectrum for normal growth. Popp's (1926) results indicate 

 that the blue-violet end of the spectrum is necessary for normal 

 growth although the ultraviolet may not be indispensable. Shirley 

 (1929) states that " The entire visible and ultra-violet solar spectrum 

 is more efficient for the growth of the plants studied than any portion 

 of it used ; the blue region of the spectrum is more efficient than the 

 red region." Schappelle (1936) concluded that white light is best for 

 normal plant response. Either end of the visible spectrum without 

 the other causes abnormal growth. Infrared, between 0.8 fi and 2.0 fi 

 was ineffective in bringing about fruiting of Marchantia, while red 

 and blue lights were of approximately equal effectiveness. 



Arthur and Stewart (1935) made a comparison of the growth of 

 buckwheat plants under Mazda, neon, sodium, and mercury vapor 

 lamps. For short periods of 8 to 10 days the sodium lamp was found 

 to be most efficient in the production of dry weight. No relation was 

 found between the absorption bands of chlorophyll and the emission 

 bands of the various lamps. These gaseous discharge lamps produced 

 plants with greener leaves than the Mazda lamps. Later Arthur 

 and Harvill (1937) show that the sodium lamp alone is not ideal for 

 the continuous growth of plants over long periods of time. If, how- 

 ever, the continuous exposure from the sodium lamps is supplemented 

 by an exposure of 2 hours per day from an 85-watt capillary mercury 

 vapor lamp, excellent leaf color and flowering could be produced in 



