144 AGRICULTURAL BACTERIOLOGY. 



forms and have hardly yet been able to satisfy themselves 

 whether they are normal growths of bacteria, or degenerate 

 forms of the organism resulting from abnormal conditions. 

 Bacteria do not as a rule produce branches from their sides, 

 but simply divide by cross division. The presence of these 

 branching forms has suggested to some students that the 

 organisms in question are really related to some of the 

 higher molds rather than to bacteria proper. Others have 

 thought that they represent a type of yeast plant, the side 

 branches representing buds characteristic of this group of 

 fungi. Other microscopists are as confident that the forms are 

 true bacteria with peculiar methods of growth under certain 

 conditions. Other bacteria are known to show unusual forms 

 when placed in unfavorable surroundings. Even the Diph- 

 theria bacillus sometimes shows branches. It is also certainly a 

 fact that similar irregular growths with side branches may be 

 induced in the organisms of the root tubercle by cultivating 

 them in ordinary laboratory culture media in which a certain 

 amount of acid has been added. But whatever be the con- 

 clusion on this matter there is no doubt that these peculiar Y 

 and T forms, bacteroids, as they are called, are a modified 

 growth of the B. radicicola that get into the root from the 

 soil. Eventually the bacteroids also disappear and a more 

 typical form of rounded bacteria is found in the tubercle. In 

 all cases the bacteria which make entrance into the root of the 

 legume appear to go through a somewhat similar series of 

 transformations during the growth of the tubercle. 



The tubercle, therefore, must be regarded as a peculiar ab- 

 normal growth of the root of the leguminous plant, stimulated 

 by the presence of the invading organisms. They are as truly 

 abnormal as are the galls produced on the leaves or branches 

 of trees by the sting of insects. They are the result of the 

 action of the presence of bacteria and clearly do not normally 

 belong to the leguminous plant itself. 



