FIXATION OF ATMOSPHERIC NITROGEN 347 



It was first definitely proved by M. Berthelot, in 1876, 

 that some plants had the power of fixing free nitrogen ; he 

 also found that, apart from the growth of plants, some 

 soils had the power of taking up nitrogen, which property 

 has since been traced to particular special bacteria contained 

 therein. 



The discovery of these organisms was due to two German 

 investigators— Messrs. Hellriegel and Wilfarth— who made 

 a special study of the small, tubercle-like bodies which had 

 long been observed on the roots of the lupin, peas, clover and 

 other plants of the same class. A microscopic examination 

 of these tubercles showed that they contained masses of 

 very short bacteria. These bacteria were then isolated and 

 cultivated, and it was definitely found it was the presence 

 of these organisms that enabled the plants to directly 

 absorb atmospheric nitrogen. 



The absolute need for the presence of these organisms in 

 soil intended for crops has been shown by the experiments 

 of Professor Nobbe on plants which have been made to 

 grow on soil that has been sterilized by heat, but which in 

 all respects has its constituents well fitted for their growth. 

 Similar plants have been grown in other portions of the 

 same earth which had not been sterilised, and while these 

 afforded good luxuriant growths, those in the sterile earth 

 scarcely rose above the ground. Experiments have also 

 been made as to the efi'ect of adding to soil substances 

 which inhibit the growth of bacteria, with effects precisely 

 similar to those mentioned above. 



Artificial cultures of these organisms have recently been 

 introduced commercially under the name ' Nitragin ' in 

 Germany, for the enriching of soils naturally poor in these 

 organisms, with the result that the crops have been largely 

 increased. 



From what has been said respecting the utilisation due 



