NO. 21 CO2 ASSIMILATION AND WAVE LENGTH HOOVER 5 



The plants were grown under controlled conditions for a few days 

 before being used in an experiment. The temperature was about 

 21° C, humidity about 70 percent, carbon dioxide concentration two 

 or three times that of normal air, the light intensity 1500 foot-candles 

 for 18 hours a day, and the root temperature about 18° C. The plants 

 were kept under these conditions except during the time observations 

 were being made. 



The light intensity obtained with the filters was never more than 

 300 foot-candles, the carbon dioxide concentration between two and 

 three times that of normal air, and the temperature about 21° C. 

 Under these conditions light was the limiting factor. 



Using the quartz mercury arc and line filters, the ratio between the 

 rate of photosynthesis at 5461 A and 4350 A remained about the 

 same for the same plant on different days as well as for different plants 

 grown under the same conditions. This furnished a means of compar- 

 ing the results with various filters throughout the course of the 

 experiment. 5461 A was used as the standard, and the ratio of 

 the rate of photosynthesis at 5461 A and other wave lengths was 

 determined. 



In order to correct for respiration, the respiration rate was deter- 

 mined before and after each light observation, and appropriate cor- 

 rections were applied to the photosynthetic rates observed. 



RESULTS 



Measurements were made at various wave lengths of the photo- 

 synthesis produced in wheat by the rays transmitted by Christiansen 

 filters adjusted to give predominantly these several wave lengths. In 

 each case the measurements corresponded to equivalent intensities of 

 radiation transmitted by the filters as determined by a thermocouple 

 placed inside the growth chamber. The direct results obtained with 

 these filters are given in table i and figure 3. Curve A represents the 

 results obtained with the large Christiansen filters and sunlight, curve 

 B those obtained with the 6-inch Christiansen filters and Mazda lights, 

 and the points marked X are those obtained with the line filters and 

 a quartz mercury arc. 



The curves show two maxima of photosynthesis — one in the blue 

 about 4400 A, and the other in the red at 6500 A. The green region 

 of the spectrum was less efifective. The maxima obtained with the 

 large filters are somewhat higher than those obtained with the small 

 filters, owing to the fact that the wave-length bands are narrower in 

 the first case. 



