NITROGEN-FIXING BACTERIA. 137 





NITROGEN-FIXING BACTEEIA. 



By J. G. LIPMAN, 



NEW JERSEY AGRICULTURAL EXPERIMENT STATION. 



THE soil may truly be regarded as a vast laboratory. The many 

 processes normally taking place in cultivated soils lead to the 

 gradual formation of plant-food, to the solution of the mineral con- 

 stituents, to the breaking down of the organic molecules into simpler 

 forms, such that are in a condition to furnish the chlorophyl-bearing 

 plants the material for the building up of plant tissue. The cycle of 

 transformation from the simple to the complex and the falling apart of 

 these complex molecules involve the activity of higher plant life, on 

 the one hand, and that of lower organisms, on the other. Primarily it 

 is the energy derived from the sun that, with the cooperation of the liv- 

 ing protoplasm, impels the atoms to enter one or another of the innum- 

 erable combinations. These atoms are, as Carlyle would put it, ' but the 

 garment of the spirit,' and the atom of carbon or nitrogen, which 

 to-day is in the leaf of the oak or in the brain-cell of man, may on the 

 next day become a structural part of some bacterial spore that is scarce- 

 ly visible even with magnification of 1,500 or 2,000 diameters. The 

 different kinds of atoms whose presence is essential in order that living 

 tissue may arise, are not many. Among the less than one dozen of 

 these, it is the migration and transmigration of the nitrogen atoms 

 that undoubtedly form the most interesting, as well as the most im- 

 portant, phase of agricultural research. Of all the elements that enter 

 into the composition of vegetable and animal substances, nitrogen is 

 the most expensive, the most evasive, the most difficult to replace. And 

 every person who at all concerns himself with questions as to the origin 

 and the development of the various forms of life, can not be indifferent 

 as to the source of nitrogen in the soil, and the factors that in one way 

 or another affect the store of nitrogen at the disposal of the living 

 world. Whence is the soil nitrogen derived? What conditions are 

 most favorable for the maintenance of an adequate supply of this 

 precious material? What means have we at our disposal for replacing 

 the losses that occur, that in the nature of things must occur? 



We should remember of all things, that the great aerial ocean, con- 

 taining as it does more than 78 per cent, by volume of gaseous nitrogen, 

 does not directly offer that element to the plant world. In order that 

 this nitrogen may become available, it must be combined with other 



