SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 95 



the spectral bands obtained with this filter is represented in figure 2. 

 These bands are much narrower than those obtained with the 6-inch 

 filters. Plate 2 shows the large coelostat and plate 3 the large filter 

 with water bath for controlling the temperature. In order to use the 

 entire width of the beam of light, which was five or six times as wide 

 as the growth chamber, a system of plane mirrors was used to reflect 

 the light to the plants. This gave a fairly uniform illumination over 

 the entire plant. 



Fig. 2. — Energy transmission curves for the 12 by 14 inch Christiansen filters. 



EXPERIMENTATION 



Wheat was germinated between layers of moist filter paper in a 

 covered glass dish at a temperature of 25° C. When the roots had 

 grown to a length of 2 or 3 cm, the young wheat plants were trans- 

 ferred to a germination net stretched over a glass dish through which 

 tap water flowed. The plants were illuminated by a 200-watt Mazda 

 lamp placed 30 cm above the netting. When the seedlings were ap- 

 proximately 4 or 5 cm in length, four individuals, selected for uni- 

 formity of size, were transferred to the growth chamber. The plants 

 were supported by means of cotton in small holes in a paraffined flat 

 cork stopper that fitted into the top of the flask of nutrient solution. 

 The flask with the plant in place was then connected to the growth 

 chamber in the manner explained above. 



