178 BOARD OF AGlilCULTUKE. [Pub. Doc. 



years it has been known that applications to other land of 

 those soils in which root tubercles are produced would cause 

 these tubercles to grow on legumes where they would not 

 previous to such inoculation ; that is, it is possible by soil 

 inoculation to have the proper organisms put into a soil 

 where they do not exist. Acting along these lines, ten or 

 twelve years ago German investigators prepared and placed 

 on the market, under the name of " nitragin," pure cultures 

 of the different kinds of bacteria for inoculating soils for 

 different legumes. As a scientific curiosity, nitragin was of 

 great interest, but in practice it oftener failed to yield satis- 

 factory results than to give them. The principles under- 

 lying the use of nitragin, however, are of great practical 

 importance ; and it was for this reason that the Bureau of 

 Plant Industry of the United States Department of Agricul- 

 ture undertook a scientific investigation of the root nodule 

 organism and soil inoculation. The results of their investi- 

 gations are oriven in Bulletin No. 71 of that Bureau, and in 

 Farmers' Bulletin No. 214 of the United States Department 

 of Afiriculture. The discussion which follows is based 

 largely upon these publications. 



Nature of Root Nodules and Conditions favorable to 



THEIR Growth. 



The organisms that produce root nodules may properly 

 be regarded as bacteria. They gain admission to the plant 

 through the root hairs, and rapidly increase in numbers. 

 The irritation thus caused in the root tissues usually results 

 in the formation of an enlargement of the root nodule. 

 These vary greatly in size and numbers. Although it is 

 probable that the bacteria which produce these nodules are 

 in different legumes of one kind, it is nevertheless usually 

 necessary for speedy and successful soil and plant inocula- 

 tion that the bacteria used be obtained from the same kind 

 of legume that it is desired to grow. That is, it is neces- 

 sary, in order to o})tain the best results, to prepare specific 

 cultures for specific crops. The amount of moisture in a 

 soil has a marked effect upon the growth of root nodules, a 



