46 Martin J. Prucha 



The addition of sugar to medium 334, up to 10 per cent, caused more 

 rapid multiplication and also the development of bacteroids. 



In medium 334 multiplication of the organisms was very slow and only 

 a few bacteroids developed in the three weeks. In medium 337 multipli- 

 cation was abundant and bacteroids developed. 



The results of inoculation are given in table 8. There were two hundred 

 and eight flowerpots, which were crowded together because of lack of 

 space. Fifty-eight flowerpots contained control plants, which were 

 scattered among the inoculated pots. The plants in forty-five of the 

 control pots developed no nodules; thirteen of the control pots were 

 contaminated, and these were located mostly among the flowerpots 

 inoculated with the organisms grown on medium 337. This contamination 

 occurred in spite of the precautions taken to prevent the organisms from 

 being carried from one flowerpot to another when the plants were watered. 

 In these experiments and in others not reported in this paper, it was found 

 that when a large number of flowerpots were used at one time it was 

 difficult to prevent infection from other sources than that of the inoculating 

 material. This was particularly true in the case of those legumes that 

 produce an abundance of nodules in the soil of this region, and when 

 the plants were allowed to grow for longer periods than three weeks. 

 The results in this experiment are marred by a certain amount of con- 

 tamination. The data in table 8 are so arranged as to show the total 

 number of nodules on all the plants inoculated with the same material, 

 and also to show the average number of nodules to each of these plants. 

 Basing the conclusions on the mere number of nodules overemphasizes 

 the importance of the contamination. When the plants were examined, 

 and the size, location, and evenness of distribution of the nodules among 

 the plants in the same flowerpot were noted, in addition to their total 

 number, much more reliable evidence was obtained. In view of this, 

 the following conclusions seemed to be warranted: 



When B. radicicola of alfalfa is propagated on media 334, 335, and 

 337 and kept for three weeks, multiplication of the organism takes place 

 and the infecting power is not lost. A slight reduction in infecting power 

 seems to be apparent on medium 337. The addition of 0.1 cubic centimeter 

 of the normal solution of HCl to 10 cubic centimeters of each of these 

 media very slightly diminished the amount of growth, but the infecting 

 power was not affected. When 0.5 cubic centimeter of the acid solution 



