10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 87 



neglected. The intensities behind these filters were approximately 

 25 per cent of the energy of diffused daylight. For many species 

 the light intensity was insufficient. Results were obtained for plants 

 in which photosynthesis was greater than respiration. The anatomy 

 and behavior of plants in the blue light resembled those in full 

 daylight. Those in red were " etiolated as in darkness (except of 

 course that chlorophyll is formed). In green, phenomena are either 

 the same as those in red or development is reduced to a minimum ; 

 the latter is undoubtedly due to a total absence of assimilation of 

 carbonic acid. In gray, development now resembles that in blue, now 

 that in red, depending on the needed quantity of blue rays being 

 small or great." 



Arthur, Guthrie, and Newell (3) have carried out a great many 

 experiments on the growth of plants under artificial conditions and 

 find the tomato the most sensitive to high light intensity in com- 

 bination with a long day period of illumination. In three series they 

 used respectively 5, 7, 12, 17, 19, and 24 hours of illumination daily, 

 with an intensity of 450, 800, and 1,200 foot-candles. The air tem- 

 perature of the first and second series was maintained at 78° F. 

 and the third at 68° F. Their results show that the tomato will not 

 withstand a 24-hour day of illumination at intensities which cause 

 little or no injury to other plants. Even 19- and 17-hour days are 

 injurious at the higher intensities. In the greenhouse experiments, 

 where the plants were exposed to 12 hours daylight and 12 hours 

 artificial light, the plants were injured. However, the rate of de- 

 velopment of this injury was decreased by this combination of day- 

 light and artificial light. The injury was characterized by the leaves 

 becoming faintly mottled with necrotic areas appearing along the 

 veins. The plants also had yellow leaves. The first signs of injury 

 appeared in five to seven days. 



In commenting on the illumination used these authors state : 



The energy value in the constant-light room calculated at 0.3 gram calory 

 per square centimeter per minute amounts to approximately 12,960 gram calories 

 per month of 30 days. The total for the month of solar and sky radiation as 

 published by the New York Observatory for June, 1929, was approximately 

 11.903 gram calories. The two energy values are similar but, as already pointed 

 out, the spectral distribution is in no way comparable. The glass-water filter 

 in the constant-light room absorbs practically all radiation of wave-length longer 

 than 1,400 niM so that the total energy value of 12,960 gram calories includes 

 only the visible region and the near infra-red of wave-length shorter than 

 1,400 m/x. 



