Studies of Bacillus Radicicola of Canada Field Pea 73 



the nine cultures on this medium, five produced nodules, two were doubtful, 

 and two produced no nodules. Culture 28 was fifteen days old and had 

 been under the influence of this medium for only fifteen days; while culture 

 25 was fifteen days old and had been under the influence of this medium 

 for one hundred and fifteen days. No appreciable difi'erence in the in- 

 fecting power of these two cultures was observed. 



Medium 310 is the same as medium 300 except that it contains 2 per 

 cent of dextrose. Five of the six cultures on this medium produced 

 nodules; one did not, and that was not the oldest culture. Comparing 

 these results -^vith those from medium 300, it seems as if the dextrose 

 protected the infecting power of the organism on this medium. 



In the last column of Table 18 the number of living organisms in each 

 culture is given, and in the next to the last column the number of nodules 

 per plant produced by each culture is given. It is seen that in all cases 

 in which no living organisms were found in a culture no nodules were 

 produced by that culture, and that the cultures in which living organisms 

 were present produced nodules. Culture 6 is the only exception, but in 

 this case only two plants out of sixteen had four and six nodules, respec- 

 tively, and the size and location of these nodules pointed to later con- 

 tamination. 



Accordmg to the above data. Bacillus radicicola of Canada field pea 

 does not los3 its mfecting power when propagated on medium 300 and 

 400 for one hundred and fifteen days. Some of the cultures on these two 

 media did lose their infecting power, but in all cases these were the older 

 cultures. This loss in efficiency is due to death of the culture, and death is 

 induced by nitrogenous media after a considerable duration. 



SUMMARY 



1. The causal organism in the case of Canada field pea nodules is Bacillus 

 radicicola. Its flagella are peritrichic, and eight was the largest number 

 found. Its group number is B. 222.2322033. 



2. Nodules developed both in light and in darkness. A larger number 

 of nodules, however, developed in darkness. 



3. Nodules developed readily both in the soil extract and in synthetic 

 nutrient solutions in which the nitrates were either omitted or replaced 

 by chlorides. The nodules continued to increase in number as long as 

 the plants continued to grow. 



