FIXATION OF NITROGEN 63 



the bacteria would be mere parasites, taking the 

 sugars and salts they required from the plants 

 without furnishing a corresponding value in return 

 in the form of nitrogenous foods. 



This may seem to some a fanciful pressing of a 

 trade analogy, but it has its foundation in experi- 

 mental fact, for from time to time it has proved 

 beneficial to give light top-dressings of Nitrate to 

 new fields of alfalfa.* This would increase the 

 vigour and resisting power of the young plants. In 

 this way only vigorous bacteria would be able to 

 force an entry, and the ultimate fixation of nitrogen 

 would be greater. Heavier applications of nitrogen 

 would prove objectionable as the bacteria would be 

 altogether excluded. 



Considerations such as these are both interesting 

 and important. They suggest why some of the 

 earlier experiments gave negative results, and hold 

 out the greatest encouragement for the future. Soil 

 inoculation, whether for leguminous plants alone or 

 for all plants, must be practised intelligently. The 

 conditions required for success are becoming every 

 day better known, and the time is not far distant 

 when it will be possible to state the exact degree of 

 benefit that can be looked for with confidence as a 

 result of soil inoculation in any given set of circum- 

 stances. Further, it is becoming every day, as a 

 result of the increase of knowledge, more possible so 

 to alter the environment as to increase the circum- 

 stances in which the practice of soil inoculation is 

 certain to prove of benefit. 



* Bacteria in Relation to Country Life (Lipman) . 



