148 SOILS AND MANUKES 



specific organism to which fixation is due had been iso- 

 lated, and preparations purporting to be pure cultures of 

 the microbe were placed on the market under the name 

 of " mtragin." The results obtained were so disappointing 

 that the sale was soon discontinued. The name, however, 

 remains, and has been applied to all subsequent prepara- 

 tions of a similar kind. 



The prophetic words of the late chemist to the Highland 

 and Agricultural Society of Scotland on this subject were 

 amply justified at the time, and would seem to preclude 

 any very sanguine expectations for the future. He pointed 

 out that the bacteria, which are the cause of the develop- 

 ment of nodules on the roots of leguminous plants, must 

 be plentifully distributed in all soils capable of bearing 

 good leguminous crops, and that the addition of a few 

 hundreds or thousands could not be expected to make any 

 very great difference. Also that, if a soil were deficient in 

 the bacteria, it would probably be because the conditions 

 were not suitable for their growth ; it would, therefore, 

 be useless to add more until the adverse conditions had 

 been discovered and removed. He thought that, if the con- 

 ditions were suitable for the growth of leguminous crops, 

 the bacteria would naturally multiply so rapidly that in- 

 oculation would be superfluous. 



When the soil is inoculated with the juice expressed from 

 the root nodules a favourable effect is generally produced 

 on the growth of plants of the same kind, but not on others. 

 It appears that each kind of leguminous crop requires a 

 particular kind of microbe. It is believed that most of 

 these micro-organisms belong to the same species, but 

 they become so modified by association with particular 

 kinds of plants that they are unable to form nodules on 

 others. If the micro-organisms from one kind of plant 

 do become associated with another they become completely 

 adapted to their new host and will no longer form nodules 



