EIGHTEENTH ANNUAL, YEAR BOOK— PART VIII 441 



The "glue" method is a modification of the soil transfer method 

 and has been advocated as a cheap but effective method of inoculating 

 the seed. * Soil, meeting the requirements mentioned above, is dried in 

 the dark, pounded to a fine powder and sifted. The seed is sprinkled 

 with a 10 per cent solution of glue (one pound of furniture glue to one 

 gallon of water) or with a solution made sticky by dissolving sugar in 

 water and is stirred until each seed is moist. Dry soil is then sifted 

 over the seed in sufficient amount to absorb all the moisture. The 

 seed is then mixed thoroly, screened and planted within a day. Small 

 seeds inoculated in this way must be sifted carefully to prevent clus- 

 ters" from remaining together. 



Several questionable features of this method may render it undesir- 

 able from the field standpoint. In the first place the glue which is 

 employed may contain substances which will injure the bacteria and 

 reduce their efficiency. Drying the soil before using may reduce the 

 vigor of the organisms and result in only partial inoculation. Exposure 

 to light or high temperatures may kill the organisms or lessen their 

 efficiency. While this method has been used to some extent in cer- 

 tain states no definite comparative results have been secured under 

 field conditions and fhis' station is not ready to recommend it as al- 

 ways reliable. Consequently, if the use of soil is considered too labor- 

 ious and expensive it would be better to procure a satisfactory, tested 

 pure culture and inoculate the seed. With the present price of certain 

 commercial cultures, less expense and labor may also be involved with 

 more certain returns secured. 



PURE CULTURES 



Soon after the discovery that the nitrogen gathering power of legumes 

 depends upon the presence of bacteria in the nodules on the roots, it 

 was suggested that pure cultures be used for inoculation, thus avoiding 

 the diflaculties attendant upon the use of soil. Pure cultures of the 

 various organisms were secured from nodules and various liquid and 

 solid substances prepared in a sterile condition were found to support 

 the growth of these organisms. Commercial preparations were made 

 and put on the market, but the results secured in practice showed that 

 there were many difficulties to be overcome before inoculation with 

 pure cultures could be made as safe and generally satisfactory as the 

 use of soil. The difficulty has been with the material upon which the 

 bacteria were grown to make commercial '"pure cultures." The bacteria 

 seem to lose their efficiency or vigor when grown on materials containing 

 nitrogen, and when introduced into the soil in such a weal-cened condition 

 are unable to enter the legume roots. When the plants are very weak 

 inoculation will occur with weak bacteria but if, as is usually the case, 

 the legumes are rather vigorous it is necessary that the organisms be 

 vigorous and active. Then, too, in diluting the cultures before applying 

 them to the seed, in drying and in other steps connected with the actual 

 inoculation, the bacteria are often weakened or killed and other bacteria 

 frequently enter and drive out the beneficial organisms. 



To overcome these difficulties, nitrogen-free materials were used and 

 the bacteria grown on these in making "pure cultures." These cultures 



