p. p.m. of Chel 138 (ethylenediaminedihydroxy- 

 phenlyacetic acid) supplied all the iron necessary 

 for normal plant growth. With wheat the iron 

 requirement was met with 10 p.p.m. ferric chloride. 

 Corn required both Chel 138 at 10 p.p.m. and ferric 

 chloride at 15 p.p.m. 



The plants were placed in the chamber and ob- 

 served a day or two to make certain they were all 

 living, then the door was installed and the cham- 

 ber sealed. Radioactive C0 2 was admitted, and 

 the plants were allowed to grow to the desired 

 stage of maturity. For harvesting the plants, the 

 C0 2 charging equipment was turned off and the 

 plants allowed to use the C0 2 until the concentra- 

 tion reached the compensation point (about 0.01 

 percent) . The door was then opened and remain- 

 ing traces of C0 2 were blown away with a fan 

 placed in the door. The large exhaust fan cleared 

 the traces of activity from the room. The plants 



were then harvested, with the operator using ade- 

 quate safety measures for handling radioactive 

 plant material. 



Growth of Soybeans 



Three crops of soybeans were grown in the cham- 

 ber. The first crop was a preliminary one to test 

 the nutrient and growing conditions in the cham- 

 ber and was not radioactive. The second crop was 

 grown with carbon-14 and harvested at three 

 stages of maturity — 28, 54, and 70 days from plant 

 ing. At 70 days the plants were mature and pro 

 duced an excellent crop of soybeans. The third 

 crop was grown only 28 days. 



Temperature in the chamber was maintained at 

 75° F. ±1.5°. Day length was 16 hours for about 

 6 weeks, then was reduced to 13 hours to induce 

 flowering. In 7 days after shortening the day- 

 length, the plants were in full bloom. 



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