October, 1909.] 



329 



Scientific Agriculture, 



of attentioD . On further investigation 

 it was concluded that the chief reason 

 which accounted for the failure was 

 the unsatisfactory nature of the medium 

 (gelatine) upon which the bacteria had 

 been grown. Gelatine differs essenti- 

 ally from the media in which the 

 bacteria normally live, i.e., the soil and 

 plant cell, principally in that it is of 

 animal oirgin, and contains large quan- 

 tities of nitrogen. With the provision 

 of abundant nitrogen at hand, the 

 bacteria are discouraged from utilizing 

 the tree supply of the air, deteriorate 

 rapidly, and either die out altogether, 

 or lose, wholly or in part, their power 

 of fixing atmospheric nitrogen. 



There was another point which had 

 been overlooked in designing the method 

 of inoculation described, but which later 

 investigation indicated had helped to 

 prevent the full success of the inocu- 

 lation efforts. During the preliminary 

 process of germination, seeds excrete 

 certain soluble substances which have 

 a detrimental effect upon the vitality 

 of the assimilating bacteria, and, as a 

 consequence, the organisms are unable 

 properly to infect the legumes, unless 

 some special steps are taken to neutral- 

 ize the poisonous effects of the excre- 

 tions mentioned. It was found subse- 

 quently, that the latter could be made 

 harmless to the seed by adding to the 

 water in which the cultures were pre- 

 pared, a small quantity of certain soluble 

 salts, or of skimmed milk. 



These points being recognized, other 

 culture media, notably agar jelly (which 

 is prepared from a kind of sea- weed, 

 and contains practically no nitrogen) 

 were tried, and these efforts were attend- 

 ed with a greater measure of success. 

 In Bavaria, for instance, during the 

 yeai'il903, ninety-eight inoculation experi- 

 ments were carried out with Hiltner's 

 agar nitragin. Of these, eighty-one were 

 favourable, nine negative, and eight 

 doubtful — a remarkably good result, 

 since in some cases, increased yields 

 followed inoculation even on soils that 

 had already borne good crops of the cor- 

 responding legume. Nobbe and Hiltner 

 also employed various liquid prepar- 

 ations as culture media in which to grow 

 the bacteria, and these were found to 

 be better adapted to maintain the 

 vitality of the organisms for a longer 

 time than agar jelly and other solid 

 media. 



Hellriegel and Wilfarth's discoveries, 

 and the results of Lawe and Gilbert's 

 work at Rothamsted excited consider- 

 able attention in the United States, 

 and extended investigations on the 

 results of inoculation with different 

 species of legume plants were started 

 42 



in that country. At first, the method 

 employed was that of inoculation by 

 means of earth from other legume 

 fields. The two crops which appear- 

 ed to benefit most by this practice 

 were the soy bean and alfalfa. In 

 the case of clover, cowpeas, field 

 peas, beans, and vetches, the organisms 

 responsible for nodule formation and 

 assimilation of nitrogen appeared to be 

 already present in most cultivated 

 soils, and these crops gave good returns, 

 and did not appearently require inocu- 

 lation. 



At a later stage the United States 

 Department of Agriculture turned its 

 attention to the subject of artificial 

 cultures of Pseudonwnas radicicola for 

 inoculation purposes. Dr. G. T. Moore, 

 of the Bureau of Plant Industry, under- 

 took the work, and devised the method 

 of preparing the cultures. Moore's 

 method differed somewhat from tnat of 

 Nobbe and Hiltner. The American 

 scientist first prepared an active culture 

 of the nodule-bacteria in a liquid 

 medium, the composition of which in- 

 cluded little or no nitrogen, in order 

 that the assimilating power of the 

 organisms might be increased. Absor- 

 bent cotton was then dipped in the 

 liquid culture, and subsequently dried 

 rapidly at a low temperature. In this 

 condition they retained a number of 

 the bacteria, and formed a convenient 

 medium for transmitting the organisms, 

 and for starting new liquid cultures. 

 With the cotton was sent out, in every 

 case, a packet containing suitable quan- 

 tities of cane sugar, potassium phos- 

 phate, ammonium phosphate, and mag- 

 nesium sulphate, which were to be dis- 

 solved in a large bulk of water, thus 

 forming a nutrient solution in which the 

 bacteria multiplied rapidly under favour- 

 able conditions when the cotton culture 

 was added. The seed to be inoculated 

 was placed in this solution for a time, 

 being afterwards dried before sowing, 



Moore's cultures were very extensively 

 tried by the United States Department 

 of Agriculture, in co-operation with 

 working farmers all over the country 

 during the year 1904. To everyone who 

 made application, a free packet of 

 inoculating material was supplied, with 

 detailed instructions as to the method of 

 using it. In this way about 12,500 tests 

 were made under the most varied con- 

 ditions, 



With the arrival of reports on the 

 results of all these trials, it soon appear- 

 ed, however, that the general measure of 

 success which had followed inoculation 

 with Moore's cultures was far below 

 what had been anticipated. It exhibits, 



