n8 Minnesota Plant Life. 



tural experiments have illustrated this fact. In Alabama, for 

 example, clover grown under conditions where the nodules 

 could not form, produced only about one-sixth as much fodder 

 to the acre as did the same kind of clover when grown in such 

 a way that the nodules could develop. All kinds of peas, beans, 

 alfalfas, clovers, vetches and other pod-producing plants, are 

 capable of producing bacterial nodules. They will not form 

 them if planted in a soil where no bacteria of the proper kind 

 exist and this is a reason why clover crops fail to do well in cer- 

 tain regions where the conditions seem outwardly favorable. 

 In Germany some laboratories have produced cultures -of nod- 

 ule-forming bacteria, which they supply to farmers under the 

 trade name of mtragin. If, now, a soil in which nodules would 

 ordinarily develop poorly, is inoculated with nitragin, the clover, 

 pea or bean crop will grow with double, triple or quadruple 

 vigor. Agriculturists may reasonably look forward to a period 

 when the soil will be regularly inoculated for a variety of crops 

 just as cheeses are inoculated for a variety of flavors. For 

 these remarkable facts the explanation is not far to seek. Dur- 

 ing their life-processes the bacteria are able to fix the nitrogen 

 of the atmosphere and develop nitrogen salts. But these ni- 

 trates and nitrites are precisely what the higher plant demands in 

 its nutrition and it seizes and assimilates them. What is for the 

 bacterium a waste-product is for the clover a food-product. In 

 return for a supply of nitrogen salts developed and delivered in 

 its root area, the clover affords protection to the bacteria against 

 desiccation and supplies them with certain of its waste products 

 for use in the bacterial economy. It is a striking fact that 

 after a crop of clover with nodules has been harvested there are 

 more nitrates and nitrites left in the soil than there were when 

 the crop began to grow, and this, too, notwithstanding that clo- 

 vers use themselves a considerable quantity of these salts. 



Bacteria and crop-rotation. From the facts above presented 

 it is possible to understand how the technical process familiar to 

 farmers and known as "crop rotation" is at bottom bacterial. 

 After nitrates or nitrites have been exhausted by the growth of 

 cereal crops, or root-crops, such as turnips or sugar beets, the 

 soil may be replenished and invigorated by the growth of some 

 pulse crop, such as beans, peas or clover. It would be a great 



