NATURAL INOCULATION 381 



bacteria from one of these plants may inoculate the other. At 

 present no other case is known of cross-inoculation. 



How to Inoculate. When the value of inoculation was first 

 discovered (1887), the method recommended was to take soil from 

 a field where the particular plant was known to grow well and 

 spread it over the new field. The soil from the old field should be 

 taken from the upper six inches and transferred, without permitting 

 it to dry out, to the new field. From 200 to 300 pounds per acre 

 is sufficient if carefully applied. As sunshine is a strong bactericide, 

 it is best to apply on a cloudy day or toward evening and immedi- 

 ately harrow in. 



Artificial cultures are made by growing the bacteria in a 

 culture solution, and applying these pure cultures to the seed just 

 before sowing or to the soil. The first artificial cultures were made 

 about 1896, but for many years were unsatisfactory, and the soil 

 method of inoculation was best up to recently. New methods of 

 handling artificial cultures have been developed and they are now 

 quite satisfactory. Full directions for using the cultures are usually 

 furnished with each kind. 



The following method has been found very satisfactory: 



Dissolve six ounces of carpenter's glue in one gallon of water. 

 Sprinkle about one pint to one quart of this solution over a bushel 

 of seed which has been spread out on the barn floor. Stir the seed 

 so that a portion of the glue solution comes in contact with each 

 seed; then scatter over the seed about a quart of soil which has 

 recently been secured from a sweet clover or alfalfa field where 

 the roots have an abundance of nodules. Again stir the mixture 

 so that some soil will be glued to each seed. If the seeds stick 

 together in little masses they may be separated readily by passing 

 them through a fine-meshed fan riddle. It is not advisable to store 

 inoculated seed for a very long time. 



Natural inoculation is sometimes secured through bacteria 

 which adhere to the seeds. This is more common with rough-coated 

 seeds like sweet clover in the hull or burr clover. It has frequently 

 been observed, in sowing alfalfa on a new field, that only an 

 occasional plant would survive the first season. Examination 

 usually shows those occasional plants to have nodules, probably 

 from bacteria on the seed. If such a field is replowed, harrowed 



