LUTHER BURBANK 



that produce the tubercles and that assist the plant 

 in securing a supply of nitrogen are closely related. 

 There are, however, different groups of micro- 

 organisms that are able to produce the tubercles 

 and help in nitrogen-fixation. 



As micro-organisms are not always present in 

 any given soil, it has been found sometimes desir- 

 able to inoculate the soil in which various clovers 

 are to be grown. 



This may be done by scattering over the field 

 soil from a field in which tubercle-bearing plants 

 of the same species have been grown in the 

 previous year. 



It has been clearly demonstrated that such 

 inoculation of the soil may lead to much freer 

 growth of tubercles than would otherwise take 

 place, and to the increased vigor and growth of 

 the clover crop. The use of artificial cultures of 

 nitrifying bacilli has also been recommended. It 

 is necessary, however, to treat the solution in a 

 particular way in order to insure that the micro- 

 organisms may maintain vitality. If they are dried 

 slowly under the usual atmospheric conditions, 

 the microbes die. 



It has been found possible to preserve them by 

 rapid drying of pieces of cotton dipped in a solu- 

 tion containing the microbes. 



The Department of Agriculture at Washington 



[100] 



