i 4 o POPULAR SCIENCE MONTHLY. 



Untiring research by many men and in many places has taught us 

 that it is the mysterious force in living protoplasm that in its aggres- 

 sive way reaches out and appropriates the restless molecules of at- 

 mospheric nitrogen; that though it destroys it also builds up. Prac- 

 tical experience had taught the ancients that crops of the legume family, 

 crops like clover, beans, lupines, etc., do not exhaust the soil to such an 

 extent as do crops not belonging to the same family. They had learned 

 that after a crop of clover they could raise a larger crop of wheat. 

 Why it was so they did not know, nor did the many generations of 

 farmers who followed them; yet not knowing they availed them- 

 selves of the advantages that time had pointed out to them. It was 

 reserved for the men of our generation, for men equipped with the 

 methods of our own day, to illuminate the darkness, to unveil for us 

 still another of nature's mysteries, to show us an intelligent way for 

 replacing the unceasing losses of nitrogen. It was scarcely more than 

 fifteen years ago that Hellriegel and Wilfarth published a series of 

 wonderfully conceived and wonderfully exact experiments that de- 

 cided for all time a much-debated question, which for a century had 

 taxed the ingenuity of the foremost scientists of Europe. What Boussin- 

 gault with all his mental penetration and clearness of vision had failed 

 to accomplish, what Lawes and Gilbert with all their painstaking care 

 and admirable equipment had failed to achieve, the German 

 investigators had made clear. They showed conclusively that in the 

 root nodules of leguminous plants there are found certain bacteria that 

 in a way still unknown to us enable the host plant to make use of the 

 gaseous atmospheric nitrogen. We do know that there is a continual 

 struggle between the plant and the invading bacteria; we are justified 

 in believing that the bacteria, compelled by the plant, unlock to it the 

 hitherto inaccessible store of nitrogen. It was in this wise, partly, that 

 the nitrogen accumulation in our soils resulted ; it was in this wise that 

 the rich prairie soils, containing at times as much as twenty thousand 

 pounds of combined nitrogen per acre to a depth of one foot, had ac- 

 quired that nitrogen. This dwelling together of two distinct forms 

 of life with mutual benefit resulting is known as symbiosis, and the 

 symbiotic life of leguminous plants and of the organism known as 

 Bacillus radicicola has made possible to a great extent the terrestrial 

 life of to-day. Yet there is another phase of the question, a phase 

 that but a few years ago had not been recognized. There are bacteria 

 in the soil that can avail themselves of atmospheric nitrogen without 

 the aid of leguminous plants. Kecent work in this field of research in- 

 dicates that such fixation of atmospheric nitrogen is of vast significance, 

 of greater moment, perhaps, than the fixation of nitrogen by legumes. 

 To understand more clearly the relations existing among the many 



