THE BACTERIAL NUCLEUS 8l 



In myxobactcria and cytophagas the rod-form of the nucleus is less marked, 

 but the equivalent cytological stages possess what is probably an equivalent 

 structure, in the form of an elongated, oval nucleus. 



J: THE FORMATION OF THE RESTING NUCLEUS 



(i, 2, 3, 4, 5, 13, 14, 19, 20, 23, 25, 27, 30, 31, 3^, 33, 35. 3^^ 40, 41, 47, 49, 60) 



The resting stages of different types of bacteria bear a considerable degree 

 ot resemblance to one another, especially in the form of the nucleus. Those 

 which have been examined by cytological methods, and properly described, 

 are the endospore of the Bacillacecv, the microcyst of myxobactcria and 

 cytophagas, the oidial spore of streptomyces and the resting cells o( Backriacece, 

 of aerobic and anaerobic Actinotuycetacea' and Mycohacteriacea.'. 



Except for the spores of streptomyces, these structures are not reproductive 

 in function, in the sense that the seeds of plants are reproductive, being 

 designed to disseminate the offspring of a single parent ; except in so far as 

 a bacterial culture, or its equivalent in nature, may be regarded as a repro- 

 ductive or genetical unit. 



The bacterial resting stages are designed tor survival. The endospore, 

 however, although highly resistant to inimical agencies, may be primarily 

 a distributive agent (Chapter IX). Most others are presumably armoured 

 mainly against inanition, the most probable adverse factor under natural 

 conditions. Even the endospore is not produced, as has been supposed, as a 

 reaction to adverse conditions, but is often most exacting in its requirements 

 of formation. 



The general characters of the resting nucleus have already been described, 

 and it is the cytological processes by which the paired, chromosome-hke nucleus 

 of the vegetative cell is transformed into an eccentrically staining, vesicular 

 nucleus, with which we are now concerned. 



In all known cases an autogamous or a sexual conjugation appears to be 

 entailed. In the formation of the microcysts of myxobactcria and eubacteria 

 this immediately precedes the maturation of the nucleus, but in streptomyces 

 and spore-forming bacilh it takes place some time previously. 



