ORIGIN AND FORMATION OF ORGANIC MATTER IN PLANTS. 911 



the production of nitrogenous matter, so that if the mineral elements 

 are present in sufficient quantity the plant makes normal growth. 

 The plant profits by the nitrogen furnished by the bacteria while the 

 latter utilize the carbonaceous matter supplied by the plant, thus 

 establishing a symbiosis. Although the process of fixation of nitrogen 

 by the organisms and its utilization by the plant has not yet been 

 clearly explained, we can understand how that, notwithstanding the 

 great quantities of nitrogen carried away from the soil with every 

 cutting of alfalfa or clover, the amount of nitrogen in the soil increases 

 rather than decreases. 



ORIGIN OF THE NITROGEN OF NONLEGUMINOUS PLANTS. 



It has been shown by numerous analyses that soils abandoned for 

 centuries to natural vegetation in which grasses predominate are quite 

 rich in nitrogen. There are mountain meadows in France which 

 during the open season are grazed by milch cows, and although this 

 involves the removal of a considerable amount of nitrogen, and no 

 fertilizers are used, these soils constantly increase in nitrogen content. 

 While soils which are continuously cultivated frequently contain not 

 more than 1£ to 2 parts per thousand of combined nitrogen, permanent 

 meadows contain 5, 7, 9, and even .10 parts per thousand. The prairies 

 of Western America are also well'stocked with nitrogen. It is inter- 

 esting to trace the origin of this nitrogen. 



Although the investigations of Yille and Atwater and those at Eoth- 

 amsted and Grignon had proved that free nitrogen intervenes in the 

 phenomena of vegetation, the process of fixation of nitrogen in the 

 soil was not understood until explained by Berth elot, who showed 

 that nitrogen is fixed in the soil by bacteria. Winogradsky culti- 

 vated certain of these bacteria in sugar solution and found that they 

 decomposed the solution, forming butyric and acetic acids and evolving 

 carbon dioxid and hydrogen. They are therefore very similar to if not 

 identical with the organisms studied by Maquenne and the author in 

 1882 x and which decomposed sugar as explained above. The latter 

 investigators, however, had no idea at that time that the ferments were 

 able to fix the nitrogen of the air, and the investigatiou is mentioned 

 simply to call attention to the fact that these ferments are very 

 widely diffused, since they were found iu all the soils studied. These 

 organisms are all anaerobic, and it would seem suprising that they 

 should grow in a medium so thoroughly aerated as arable soil; but 

 this has been explaiued by Winogradsky as follows: The organisms 

 which fix nitrogen are capable of action only when associated with 

 certain common species of organisms which are capable of oxidizing 

 organic matter and which thus surround the anaerobic forms with 

 an atmosphere charged with carbon dioxid and deprived of oxygen. 

 Winogradsky further suggests that the hydrogen set free in the 



1 Ann. Agron., 9 (1883), p. 5 ; 10 (1884), p. 5. 

 16733— No. 10 2 



