FIXATION OF NITROGEN BY BACTERIA 2OI 



genous compounds. Pieces of cotton wool were soaked 

 in the culture and then dried ; in a dry state attached to 

 cotton wool the organisms retain their vitality for a year 

 or two. Along with the infected cotton wool two 

 packets of nutrient salts were supplied, one containing 

 sugar, magnesium sulphate, and potassium phosphate, 

 the other ammonium phosphate. The first packet was 

 dissolved in water, and the cotton wool then added. In 

 this solution the common bacteria of the air and water do 

 not grow freely, but the nodule organisms readily multiply 

 in it. After twenty-four hours the ammonium phosphate 

 is added, to encourage further development of the nodule 

 bacteria. If growth is satisfactory the liquid becomes 

 opalescent or milky, after which it is used to sprinkle 

 over the seeds ; these are then allowed to dry, and are 

 sown afterwards in the ordinary way. 



More recently cultures similar to those of Moore have 

 been issued under the name Nitro-bacterine. 



The practical utilization of pure cultures of the 

 " nodule-forming " organisms is still in the experimental 

 stage, in spite of the large amount of attention which 

 has been given to the problem. It is quite certain 

 that in certain cases seed inoculation in the manner 

 described above has been very beneficial and remunera- 

 tive, but exact knowledge of the conditions which ensure 

 an increased yield after such inoculation is still wanting. 

 The evidence seems to point to the conclusion that on 

 much of the cultivated land in Europe the use of 

 " nitragin " or " nitro-bacterine " is quite unnecessary for 

 the growth of good crops of the ordinary leguminous 

 plants, the soil being already well supplied with 

 organisms of the right kind for the adequate infection 

 of the roots of the crop. Failure to obtain increased 



