THE BACTERIAL NUCLEUS 67 



granules which surround the nucleus and which probably represent the 

 elementary chromosomes. 



The germination o{ the cyst in Azotohacter is also entirely comparable 

 with the similar germination processes in other bacteria. The vesicular resting 

 nucleus divides into two chromosome complexes and then into the four of 

 the active nucleus, at which stage the cyst is ruptured and the vegetative cell 

 escapes. 



F: COMPLEX VEGETATIVE REPRODUCTION 



(8,9, 10, 27, 31,41, 52) 



This mode of reproduction is common, although not invariably present, 

 in many types of bacteria, but does not appear to be found in spore-bearing 

 cubacteria. The nuclear appearances which accompany it are very striking. 

 Filamentous forms arc common in fdms made from such cultures, but in 

 contrast to the fdaments which occur in rough cultures, which are multi- 

 cellular, repeating in each unit of the chain the nuclear pattern ot the individual, 

 the reproductive fdaments are unicellular and their nuclear material is arranged 

 in a distinctive manner. Such fdaments may, however, occur in cultures of 

 both smooth and rough morphology, and even in cocci. Although there are 

 recognisable differences between the various types the general plan is simdar 

 in all of them. The slightly spiral morphology of the individual bacterium 

 is more clearly shown in these elongated cells, which, because they are curved 

 in two dimensions are difficult to photograph in such a manner as to keep 

 their entire length in focus. 



In smooth cultures, the shortest fdaments, which are about twice the 

 length of a single bacterium, have their chromosomes packed together at 

 the centre of the cell. Where they can be distinguished separately they are 

 invariably found to consist of three pairs. Filaments of slightly greater length 

 contain six pairs of bodies, which may be together at the centre ot the cell, 

 or at a later stage, distributed in pairs throughout the length ot the fdament. 

 This increase represents a single nuclear division within the fusion cell. A 

 < second nuclear division occurs after the chromosome pairs have been 



