INOCULATION 331 



to another. For this reason, it is sometimes necessary in 

 introducing a new legume into a community to supply it with 

 the proper bacteria by means of inoculation. As the bacteria 

 are very small and increase rapidly under favorable condi- 

 tions, a small quantity of them will inoculate a considerable 

 area. One of the best methods of inoculation is to take 

 a quantity of soil from a field on which the crop in question 

 has been growing and scatter it on the field to which it is to 

 be introduced. This operation is sometimes expensive, 

 particularly if the soil has to be shipped some distance, as 

 the transportation charges will then be heavy. Five to 

 eight hundred pounds of inoculated soil should be applied to 

 each acre of the new field if the inoculated soil can be obtained 

 close at hand. If it must be shipped from a distance, from 

 200 to 300 pounds may be made to suffice, thus reducing the 

 expense ' of transportation. This inoculated soil may be 

 mixed with several hundred pounds of ordinary soil before 

 it is applied, as the larger quantity can be spread more easily 

 and evenly. It is often better to start a small plat and 

 then use soil from it to inoculate larger fields. 



Where the distance from an old field makes inoculation 

 by soil transfer too expensive, what is known as the ''pure 

 culture" method of inoculation may be used, though it is 

 less generally successful than the other methods. The 

 bacteria are grown artificially in culture media, and shipped 

 either in the dry form similar to cakes of yeast, or in tubes 

 containing the liquid solution. Before using the powder 

 or liquid it is put into a vessel containing water, a little 

 sugar, and other suitable material for the growth of the 

 bacteria. In a few days the water takes on a milky hue from 

 the large increase in numbers of the bacteria, and it is then 

 sprinkled on the seed or is mixed with soil and spread on the 

 field. It is much easier to inoculate the seed, which should 

 then be sown within a few days. As the desired bacteria 

 are present in small numbers in most soils and are usually 



