The excised nodulated roots were placed in 500 mlbottles sealed with a rubber septum. 50 ml of air were taken and thesame volume of acetylene gas introduced into the bottle, incubatedat 37◦C then samples from root atmosphere in bottles were with-drawn and injected to the gas chromatograph. Afterwards nodulesof each individual root were counted and nodules fresh and drymass were measured. A calibration curve was constructed usingpure ethylene.