Studies. OF Bacillus Radicicola of Canada Field Pea 59 



In making any deductions from the preceding data, it must be remem- 

 bered that the plants in this and in the other experiments were grown 

 under special conditions. If the number of nodules on the plants in this 

 experiment were dependent only on the degree of infectmg power of the 

 organism, an excellent illustration of variation in the infecting power 

 would here be shown. This variation would, in this case, be due to the 

 nature of the medium in which the organism was propagated. 



That the number of nodules on a plant may be influenced by other 

 factors than the infecting power of the organism has been shown in Part 

 II of this paper, and also by experiments of other investigators. But 

 the part that such other factors have played in this second test must be 

 only a conjecture. 



In order that a nodule may be produced, it is necessary that at least 

 one organism shall come in contact with the root, that it shall enter the 

 tissue of the root, and that it shall multiply inside the tissue. At least 

 six factors can be mentioned which may have been of some importance 

 in this experiment in bringing about this result : 



1. The distribution of the organisms through the entire volume of the soil 

 in each flowerpot. — The plant roots grow rapidly during the first three 

 weeks after planting, and unless the organisms are evenly distributed 

 through the soil a variation in the number of nodules might result if the 

 plants are not allowed to grow for more than three weeks. Watering 

 would tend to bring about an even distribution. All the flowerpots were 

 watered twice each week, but the amount of water introduced into each 

 pot was not measured — although it was uniformly constant — - and be- 

 cause of this the distribution of the organisms throughout the soil may 

 not have been uniform in all the flowerpots during the first two weeks. 



2. The number of organisms introduced into the d'fjerent flowery ots at the 

 time of inoculation. — There is no available evidence to show how important 

 this factor may be. That it may have exercised some influence seems 

 highly probable. Reference to table 10 shows that there was a very 

 great difference in the total number of organisms in the various cultures, 

 and consequently the flowerpots inoculated with these cultures did not 

 receive the same number of organisms. 



3. Multiplication of the organisms in the soil after inoculation. — Bacillus 

 radicicola multiplies readily in the sterilized soil that was used for growing 

 the plants. This does influence the total number and the distribution 



