﻿AIR AND LIFE. 39 



Is there no otlier supply, and especially, is there no method by which 

 pure atmospheric nitrogen may be also utilized by plants? In view of 

 the considerable amount of nitrogen contained in atmosphere, the mat- 

 ter is one of great importance to plants. 



The question has been answered by Hellriegel.^ After twenty-five 

 years' investigation, the learned director of the agricultural station of 

 Bemberg has finally proved conclusively that certain plants at least 

 have the power of assimilating atmospheric nitrogen. These plants 

 belong to the leguminous family. While cereals, for instance, need to 

 be provided with nitrogen under the form of nitrogenous compounds 

 mingled with the soil, or under the form of nitrates or ammonia salts, 

 lupines, pease, clover and such plants do very well without sach com- 

 pounds. And yet they contain nitrogen ; moreover, agriculturists know 

 that they not only do not require nitrogenous manure, but that after 

 they have been grown on a soil they contain more nitrogen than the 

 soil could possibly have furnished; hence the name of "bettering 

 plants." If they are buried in the soil, they not only restore the 

 amount of nitrogen which they may have derived from it, they add to 

 it an excess which they have obtained elsewhere; that is to say, from 

 the atmosphere. Plants grown in a soil totally deficient in nitrogen 

 contain much more of it than the seeds from which they spring — i^ro- 

 vided, however, one condition is fultilled. This condition is that the 

 roots possess certain peculiar outgrowths or small tumors — nodules, as 

 they are commonly called — in which a special sort of bacteria is found. 

 If the bacteria are wanting, the plant does not grow well; it remains 

 puny and deficient in nitrogen, but if watered with water to which has 

 been added a culture of the requisite species of bacteria it becomes 

 thrifty and yields an amount of nitrogen amounting to a hundredfold 

 the weight contained in the seed. 



It seems that in different species of leguminous plants the active 

 and important species of bacteria are different. That which is adapted 

 to acacia, for instance, although it does not suit pease, works well 

 with beans, and vice versa. Are we to draw the inference that each 

 species of this family has its own special bacterium? Nobbe is not of 

 this opinion; he thinks there is only one species, which he calls Bac- 

 terimn radicoJa ; but that within this species a number of races or 

 varieties has been evolved, each one specially adapted to a sort of 

 communalism with a particular species of plant. For instance, if one 

 individual of this bacterium lives in the nodosities of one particular 

 plant, its progeny becomes specially adapted to life on the same species, 

 and does not thrive on another species. Such is Kobbe's view briefly 

 summarized, and it would explain many curious facts noticed by 



^Hermann Hellriegel, born 1831, died September, 1895. This important work was 

 accomplisbed with the cooperation of Mr. Wilfarth, and was made known in 1886 at 

 the Natiirforscher-Versammhino; in Berlin. Varro and the old Koraan farmers had 

 noticed that beans, lupines, and vetches render the soil more fruitful, but Hellriegel 

 and Wilfarth discovered the reason. 



