146 AGRICULTURAL BACTERIOLOGY. 



firmed, it is evident that we owe the power of fixing nitrogen 

 to the microorganism. With the exception of Beyerinck and 

 Maze, no one has yet been able to demonstrate any consider- 

 able fixation of nitrogen by the action of bacteria growing 

 alone in laboratory culture media. 



A second suggestion is that the leguminous plant fixes the 

 nitrogen through the agency of its leaves or roots, the bacilli 

 in the roots merely serving as a stimulus to increase the 

 normal functions of the plant. Those who have adopted this 

 view have insisted that the power of fixing nitrogen is a very 

 widely distributed function of almost all green plants. They 

 have claimed that many other plants, wholly unassociated with 

 microorganisms, are capable of fixing small amounts of 

 atmospheric nitrogen. This is said to be true of many green 

 algae growing in water, of mustard, of oats and a host of other 

 plants, the legumes differing only in the amount of nitrogen 

 assimilated. 



It is extremely doubtful whether this conclusion is correct. 

 The general consensus of experimental work denies the possi- 

 bility of nitrogen fixation by ordinary green plants. It is, 

 therefore, at the present time not generally believed that the 

 legume, or any other green plant, has of itself any power 

 of fixing nitrogen. It is certain that if the green plants do fix 

 nitrogen through their leaves the amount thus fixed by the 

 ordinary plant is extremely small and not to be compared with 

 the large quantity fixed by the legumes under the influence of 

 the root nodules. Neither the ordinary plant under any con- 

 dition, nor the leguminous plant without the agency of the 

 bacteria in the nodules, has the power of fixing an amount of 

 nitrogen which is appreciable to ordinary chemical analyses. 



A third suggestion as to the phenomenon is that the fixa- 

 tion of nitrogen is the combined result of the organisms acting 

 together. Exactly how this occurs is wholly unexplained, 

 even by hypothesis. It is a well-known fact that there are 



