210 Bacteria in Relation to Country Life 



periments of others which pointed in the opposite direc- 

 tion. 



New evidence was accumulated, in the course of 

 time, which again opened the question of the utiUzation 

 of atmospheric nitrogen by plants. Field and pot ex- 

 periments, carried on in Germany, France, England 

 and the United States, in the early eighties, furnished 

 abundant proof that, under some conditions, the plants 

 of the legume family possess the unmistakable ability 

 to secure nitrogen from the atmosphere. The investi- 

 gations of Atwater in this country, in 1883 and 1884, 

 demonstrated the ability of legumes to acquire the 

 nitrogen of the air. In some of his experiments with 

 peas, the nitrogen gained was 50 per cent more of the 

 total quantity harvested. This gain was ascribed by 

 him to the direct utilization of the free nitrogen. 



The solution of the problem. — The mystery was cleared 

 up in 1886 by Hellriegel at a meeting of scientists in 

 Berlin. Hellriegel, and Wilfarth, who was associated 

 with him, noticed in their experiments that when peas 

 were grown in artificial soil containing no combined 

 nitrogen, but provided with mineral plant-food, they 

 developed normally until all of the nitrogen in the seed 

 was used up, when they turned yellow and perished. 

 There were, however, occasional plants which passed 

 through this critical period. Such plants again assumed 

 a healthy green color and grew vigorously to maturity. 

 The examination of these plants showed that their 

 roots invariably contained nodules, whereas the plants 

 which perished contained none, or only an occasional 

 small nodule. 



