22 Martin J. Prucha 



a pure culture of Bacillus radicicola. After twenty-four days the plants 

 were examined for nodules. 



Results 



All the plants developed plenty of nodules. The inoculation with the 

 pure culture had no apparent effect on the number of nodules. The soil 

 extract was not sterilized and apparently had plenty of the organisms. 

 The plants whose roots were kept in darkness had a greater abundance 

 of nodules than those whose roots were exposed to light. The aeration as 

 supplied in this experiment had no stimulative effect on either the number 

 or the size of the nodules. 



EXPERIMENT 2 

 INFLUENCE OF SOME NUTRIENT SOLUTIONS IN LIGHT AND IN DARKNESS 



Ninety Erlenmeyer flasks of 300 cubic centimeters capacity were 

 divided into five series, with eighteen flasks in each series. These flasks 

 were filled with the following solutions, respectively: series 1, with medium 

 101; series 2, with Crone's solution; series 3, with Pfeffer's solution; series 

 4, with tap water; series 5, with soil extract (the same as was used n 

 experiment 1). Six flasks from each series, three covered with black 

 paper and three not covered, were inoculated with a pure culture of Bacillus 

 radicicola. A second group of six flasks from each series were prepared in 

 the same manner, but each flask was inoculated with 5 cubic centimeters 

 of soil extract. A third group of six flasks from each series were prepared 

 in the same manner but were not inoculated. One plant was grown in 

 each flask. The water of transpiration was replaced each week. At the 

 end of four weeks the plants were examined for nodules. The results are 

 given in table 2. 



Results 



Not all the plants that were inoculated developed nodules. A few 

 nodules developed on the plants grown in medium 101, in Crone's solution, 

 and in Pfeffer's solution. In the soil extract all the plants developed 

 nodules, although the plants grew better in Crone's solution and in Pfeffer's 

 solution. In the tap water no nodules developed. More nodules 

 developed on the roots kept in darkness than on those exposed to the 

 light. 



