BY R. GREIG SMITH. 153 



We have to remember that Prazmowski saw that the infecting 

 thread contained rod-like cells, and that Maria Dawson while 

 corroborating this noted that the gelatinous membrane (capsule) 

 of the tube either became dissolved, whereby the rods were 

 liberated, or the .cells budded off Dematiuin-li^e. There is no 

 reason to suppose that the same thing does not occur with the 

 bacteroids; it is as unnecessary to suppose that the branching- 

 infecting thread is of a nature different to the branching bac- 

 teroids as that the cells in a chain of bacilli differ from a single 

 isolated cell of the same species. The y form of Rhizobium differs 

 from the Y form only in the age of the daughter cells. In the y 

 form one or both of the daughter cells are immature (buds), while 

 in the Y form they are mature (rods) and ready to escape from 

 the enclosing membrane. There should never have been any 

 question of degeneration or of specialisation : they are simjDly 

 normal cells. Beijerinck has shown that the nature of the capsule 

 can be altered at will in artificial media, and that forms precisely 

 similar to those seen in the nodule can be obtained in artificial 

 culture. The condition necessary for this appears to be the 

 presence in the faintly acid culture fluid of potassium phosphate 

 and a thin layer of fluid in the culture flasks. 



They and Y bacteroidal forms are always observed in the young- 

 cultures in artificial media : in old cultures only the rod forms 

 are present. This is the case not only with the nodule-former, 

 but also, according to Sewerin and corroborated by the writer, 

 with Mycohacterium denitrificans, an organism that produces 

 similar branching forms in young (24 hours) cultures. This is in 

 itself enough to negative the idea that these are degeneration 

 forms, and, as I have pointed out, the specialisation hypothesis is 

 unnecessary. 



As for Hiltner's view that the baateroids are large bacteria, it 

 is quite possible, but it is not always so, as in working with the 

 lupin bacteroids I have seen little difference in size between the 

 cells contained within the bulky capsule and the cells obtained 

 in artificial culture. Bacteria undoubtedly differ in size accord- 

 ing to the media in which they are cultivated, and, as I have 



