NO. 2 PLANT GROWTH AND WAVE-LENGTH BALANCE JOHNSTON 3 



ducing the infrared or by increasing the intensity of the rest of the 

 spectrum. An experiment was therefore planned in which this was 

 partially accomplished by building up the blue end of the spectrum. 



Experiment i. — Two i,ooo-watt projection Mazda lamps (115 v.) 

 were placed i meter apart. Surrounding each lamp was a clear Pyrex 

 thermos bottle blank fitted with a water inlet and outlet. The radiation 

 of each lamp was thus filtered through 5 mm of water. The constant 

 flow of water through this jacket was a great aid in maintaining a 

 constant temperature condition in the room, since a great deal of heat 

 was thus removed. 



A copper sulphate (sp. gr. 1.08, about 8 percent) filter (6 cm thick) 

 was placed in front of one of the lamps. This was the added blue 

 light source. The individual rotating plant cultures were located 

 at positions relative to these two light sources which gave the intensity 

 values expressed as watts/cm^ in table i. 



Table i. — Radiation intensities and plant data from experiment i 



Light intensity 



watts/cm^ Stem Total 



Culture . ^^ > ht. dry wt. 



no. White Blue Total cm gram 



1 0396 .0006 .0402 5.0 .086 



2 0285 .0010 .0295 7.1 .102 



3 0166 .0014 .0180 6.1 .043 



4 0064 .0027 .0091 6.3 .025 



5 0046 .0054 .0100 3.8 .019 



Marglobe tomato seeds were sprouted between moist filter paper 

 at a temperature of 25° C. for 3 days. The sprouted seeds were then 

 transferred to a germination net, and after about a week of growth 

 five similar seedlings were selected and set out in quart jars, one per 

 jar, and placed on the five small rotating tables. After 2 weeks of 

 growth these plants were measured and dried in an oven at 103° C. 

 to obtain the dry weight. These data are also shown in table i. 



Because of the meagerness of data, no definite conclusions can be 

 drawn. The first three plants were heavier than similar ones grown 

 in the north and south laboratory windows. Although the total in- 

 tensity of no. I was greatest, yet maximum dry weight occurred in 

 plant no. 2. Here the added blue radiation was about 3 percent of 

 the total as compared to 1.5 percent in plant no. i, which was yellow- 

 green in color. Plant no. 2 was a light green when compared to plants 

 3, 4, and 5, whose percentage of added blue to total radiation were 

 respectively 8, 30, and 54. 



