CHEMICAI, CHANGES 221 



previously been estimated; the gain in nitrogen is a measure of 

 the nitrogen-fixing power. 



The culture solution is prepared as follows: Water 1,000 cc. 

 mannite 15 grams; potassium phosphate 5 grams; magnesium 

 sulphate 0.2 grams; calcium chloride 0.02 gram; and ferric 

 chloride, 2 drops of a 10 per cent, solution. The solution is then 

 made alkaline with sodium hydroxide, and sterilized. Brown re- 

 ports that much more satisfactory results may be secured by the 

 use of a'soil as the medium for the culture. 



We have as yet no evidence that the quantity of nitrogen 

 assimilated by these bacteria, is of importance under ordinary 

 agricultural conditions. 



Experiments at the New Jersey Experiment Station 1 indicate 

 the possibility of the addition of nitrogen to the soil in this way. 

 An analysis of the soil at the beginning and end of two years, 

 together with the estimation of the nitrogen in the crops har- 

 vested, showed an undoubted gain of nitrogen. 



Assimilation of Elementary Nitrogen by Legumes. The fact 

 that certain kinds of plants can utilize atmospheric nitrogen was 

 not discovered until about 1882. At that time, Hellriegel 2 

 demonstrated this fact by experiments described briefly as 

 follows : 



Lupine seed were planted in pots of soil which had been heated 

 sufficiently to destroy all forms of life in it, and which had been 

 subjected to analysis so that the exact amount of nitrogen present 

 in the quantity of soil taken was known. All the pots were pro- 

 tected from bacteria and watered with sterilized water. To one 

 series of pots, there was added a small amount of an aqueous 

 extract from a soil in which lupines had grown well. To the 

 other series, no addition was made. When the plants were 

 grown, they were dried, and weighed. The quantity of nitrogen 

 in the plants, and in the soil remaining in the pots, was determined 

 by chemical analysis. As the nitrogen originally present in soil 



1 Report for 1907, p. 168. 



2 Exp. Sta. Record 5, p. 835. 



