Bacteria and the Nitrogen Problem. 519 



roots of a legume. Furthermore, it seems as though the plant 

 actually uses the contents of these tubercles, for at the end of the 

 season the tubercles are found to be much softer and shrunken, and 

 are practically emptied of their mass of bacteria. 



Effect of Tubercles. 



It is a well-established fact, and has been shown by a number of 

 independent investigators in various parts of the country, that the 

 leguminous crop which bears tubercles will exceed a similar crop 

 without tubercles by from 100 to 1,000 per cent; that is, a field of 

 clover grown on such pour soil that it would only yield 200 pounds to 

 the acre would be so invigorated by the pi-esence of tubercle-forming 

 bacteria that on exactly similar soil it would produce from 400 to 

 2,000 pounds to the acre, and this without any cost whatever for 

 fertilizers and with very little more labor. In addition to the 

 increase of the actual weight of the crop, tubercles also cause the 

 plants to flower and fruit earlier, and the number of seeds produced 

 is very much greater. 



Thus it will be seen that it is worse than useless to attempt to grow 

 any leguminous crops without being certain of the presence of the 

 l^acteria which enable the plant to fix free nitrogen. It would be 

 much better to fertilize heavily and attempt to raise some more 

 profitable crop than to introduce clover or beans or some other legume 

 for the purpose of enriching the soil. It can not be too strongly 

 emphasized that imless the tubercles are present the leguminous crop 

 is of absolutely no more benefit to a soil than wheat or potatoes. 



While these organisms are pretty generally distributed through- 

 out the earth, and it is quite possible in many parts of the country to 

 grow almost any leguminous crop and secure these tubercles, it is 

 also true that certain regions are practically devoid of the right kind 

 of bacteria, and that unless some artificial means of introducing the 

 germs be resorted to the crop will be a failure. 



Artificial Inoculation of the Soil- 

 In the past there have been two methods used in attempting to 

 bring about artificial inoculation. Naturally where a certain 

 leguminous crop has been grown successfully for a number of years 

 the soil will become filled with tubercle organisms, and by transport- 

 ing this earth to new fields the organisms will thus become available 

 for forming the nodules in localities where they previously had not 

 existed. This was the means by which the soy-baan organisms were 

 brought from Japan, and there are very few places in this country 

 where soy is now grown that did not receive their inoculation, 

 indirectly at least, from the Japanese soil. 



There are two serious objections to soil inoculations, however. One 

 is the expense, for it requires anywhere from 500 to 1,500 pounds of 

 earth per acre to produce a satisfactory growth of tubercles, and if 



