726 Soil Inoculation in the United States, [march, 



in Germany. It was after the pure cultures prepared in this way 

 were found to be unreliable in their effect that the Laboratory 

 of Plant Physiology of the Department of Agriculture, under 

 the direction of Dr. George T. Moore, undertook a scientific 

 investigation of the root-nodule organism ; and, as a result, it is 

 believed that a thoroughly practical and satisfactory method of 

 bringing about artificial inoculation has been devised. 



The nature of the nodule-forming organism was very carefully 

 investigated, and it was found to be a true micro-organism, 

 having three well-defined stages consisting (i) of minute motile 

 rods which produce the infection and frequently form zooglcea 

 masses ; (2) larger rods, either motile or non-motile ; and (3) 

 capsulated forms, the so-called "branched organisms," which 

 are made up of two or more rods held together in a sheath. 



Owing to the frequently observed fact that one kind of legume 

 would not produce nodules in soil which abundantly supplied 

 another legume with these growths, it was supposed that each 

 legume required a special and peculiar nodule organism. Dr. 

 Moore's experiments show, however, that there is but one species 

 which is described as Pseudomonas radicicola (Beyerinck). 

 The difference in the infective power of bacteria from different 

 hosts is due to slight physiological variations which can be 

 readily broken down by cultivation. 



With regard to the mode of cultivation, the usual method of 

 growing the nodule-forming organism has been to make a 

 medium from a decoction of the particular legume upon which 

 the organism originally grew. The number oi organic and in- 

 organic substances in both solid and liquid media upon which 

 Pseudomonas radicicola will thrive is, however, very great. 

 More than fifty different combinations, consisting of various 

 nutrient salts, such as magnesium sulphate, potassium phosphate, 

 ammonium phosphate, together with peptone, sugar, glycerine, 

 asparagin, as well as potato, cabbage, &c, have been found 

 to produce at least a fair growth, although an extract 

 of the host plant, plus 1 to 3 per cent, peptone, with about 

 2 per cent, cane sugar, will give the most luxuriant growth in 

 the shortest time. As a result of numerous trials, however, 

 it has been found that although the bacteria increase most rapidly 

 upon a medium rich in nitrogen, the resulting growth is usually 



