106 ELEMENTARY AGRICULTURAL CHEMISTRY 



than the previous cultures. The German products contained 

 their bacteria in dried agar-agar jelly, and were prepared for 

 use in a medium containing milk, peptone and grape sugar. 

 The American product consisted of cotton-wool impregnated 

 with a culture of the particular organit-m and dried. The 

 cotton-wool was introduced into a solution containing sugar, 

 potassium phosphate, magnesium sulphate and ammonium 

 phosphate. In this medium the organism developed. In both 

 cases it was claimed that if the seed be moistened with the 

 medium containing the appropriate organisms and dried, the 

 presence of the nitrogen-fixing bacteria when the seed is sown 

 would be ensured. 



A considerable sensation was created by popular articles, in 

 which it has been stated that the use of these cultures of 

 nitrogen-fixing organisms, under the name of **Nitro-bac- 

 terine," is destined to revolutionise agriculture, but it should 

 be remembered that the most that can be expected of these 

 methods is that the soils rich in the mineral elements of plant 

 food, but deficient in nitrogen, may be gradually enriched in 

 that constituent so as to become capable of supporting the 

 growth of ordinary crops. There seems to be little doubt that 

 the new cultures possess the power of inducing nodule-forma- 

 tions on the roots of leguminous plants, and that even in soils 

 in which nodules are spontaneously formed, inoculation of the 

 seed with the cultures ensures the formation of more numerous 

 and larger nodules. But, on the large scale, these preparations 

 have not been successful enough to secure their general adoption. 



Artificial or Chemical Manures. — The organic manuies, 



as a rule, contain all the ingredients necessary for plant life, and, 

 IS general manures, are highly satisfactory. Cases often arise, 

 /lowever, in which a soil only requires the addition of one or two 

 fertilising substances in order to fit it to yield a full crop. In 

 such cases, by means of suitable artificial manures, it is possible 

 to add exactly what is required, without introducing other plant 

 food, with which the soil may be abundantly supplied. 



