H 2 AGRICULTURAL BACTERIOLOGY. 



must be classed with bacteria and the name Bacillus ra did col a 

 was given to them by Beyerinck, who first studied them with 

 care. They are undoubtedly organisms belonging to the 

 general group of bacteria, but they are somewhat peculiar in 

 their methods of growth. In the laboratory culture media 

 they grow like ordinary bacteria (Fig. 2 1 , B) but in the roots 

 of the legume, inside of the tubercle, they produce forms un- 

 like most of the more common bacteria. At certain stages of 

 the development, by branching or budding, they produce what 

 are called Y and T forms, a method of growth not characteris- 

 tic of bacteria in general (Fig. 22, A). It is found also that 

 after the beginning of the formation of the tubercle, long, 



FIG. 21. 



The root tubercle organism, B. radicicola, under different conditions. (Maze.) 



thread-like masses, filled with bacteria, can be seen extending 

 among the tissues of the plants. These long threads appeal- 

 almost like pouches in which the bacteria are held, but they 

 eventually disappear and the bacteria themselves diffuse some- 

 what through the tissues. These phenomena, the Y and T forms 

 and the pouch-like threads, have been puzzles to the bacteriol- 

 ogists, for they are not characteristic of any other bacteria 

 known. It has been doubted whether the organisms should 

 be called bacteria. These organisms, whether true bacteria or 

 not, still retain the name originally given tln-m and are now 

 well known. They have been found universally characteristic 

 of root tubercles and many bacteriologists have made extended 

 studies with them. 



