Studies of Bacillus Radicicola of Canada Field Pea 39 



or glucose, preferably the former, has given best results m a 1 of the work 

 connected with the experiment." 



In the following pages data are presented on experiments conducted 

 through several years in an attempt to alter the " virulence "• — that 

 is, the infecting power — of the organism. In experiments 10, 12, and 13, 

 Bacillus radicicola of Canada field pea was used; in experiment 11 that 

 of alfalfa was used. The organisms were propagated and kept on various 

 media. Their infecting power was tested and measured by the nodule 

 development in plants grown in a sterilized sandy soil. 



EXPERIMENT 10 

 INFLUENCE OF CLAY, LOAM, SAND, AND CARBORUNDUM 



In this experiment the organism was grown on clay, sandy loam, sandy 

 soil, fine quartz sand, coarse quartz sand, and carborundum. One hundred 

 grams of each substance, air-dried, was introduced into Erlenmeyer flasks 

 of 300 cubic centimeters capacity. After sterilization the media were 

 heavily seeded with B. radicicola. This was accomplished by introducing 

 into each flask the growth of B. radicicola from one agar slope, along 

 with the necessary quantity of water. The amount of moisture added 

 to each medium was about five per cent less than its capacity for holding 

 water. 



Two series of flasks were prepared. In series 1 the media, as soon 

 as seeded with the organism, were spread on sterile paper and allowed 

 to dry at room temperature. The time required for their complete drying 

 was about six hours. In series 2 the media were left in the flasks, plugged 

 with cotton, and allowed to stand in the laboratory. Drying of the' 

 media in this series was very gradual. The infecting power of the organism 

 in these cultures was tested by inoculating plants. For this purpose 

 Canada field peas were grown in sterilized soil in flowerpots, and were 

 inoculated with the respective cultures at the time of seeding. Inoculation 

 was accomplished by scattering one gram of the inoculating material 

 over the soil in the flowerpots. The first test was made when the cultures 

 were ten days old and the second test when the cultures were forty- 

 six days old. When the plants were three weeks old they were 

 examined for presence of nodules. The results are presented in tables 

 5 and 6: 



