Ri: PRODUCTION 87 



Division can never be truly simple, but must always entail division of the 

 nucleus, the formation ot a transverse, membranous septum and the secretion 

 of nev^ cell walls, at the same time as the growth of the cell must itself 

 continue. Complementary to the production of structures pecuhar to cell 

 division the entire organism increases in size, extends its membrane and wall, 

 its cytoplasm and nuclear material. 



There does not appear to be any considerable difference between the 

 process of fission as it occurs in cultures at different nuclear phases. It is most 

 rapid in very young cultures, in the primary phase, but is more regular in 

 shghtly older cultures, where the standard complement of two nuclear units 

 per cell has been achieved. It is often irregular in cultures where the nucleus 

 has adopted the rod-form. In this case the length of the cellular units may 

 be very diverse. 



Bacteria possess a marked polarity, and almost invariably divide trans- 

 versely. This is also true of many cocci, which elongate and divide always 

 in the same plane, although in others, notably the commoner types of 

 staphylococci, each division is at right-angles to the previous one. This 

 results in the production of the typical, grape-like clusters. 



Rod-shaped bacteria, growing under adverse conditions, may produce 

 pathological forms which divide hi an irregular manner, but this rarely occurs 

 in healthy cultures. 



Those genera of stalked caulobacteria in which the stalk is attached laterally 

 to the bacterium divide transversely, in the usual manner, the stalk dividing 

 also. Some of those in which the stalk is terminal have been described as 

 dividing longitudinally. Where this occurs (and it does not always do so. 

 Chapter VIII), there is reason to believe that it is not the polarity of division 

 but the shape of the organism which has changed ; the former short axis 

 having been increased at the expense of the long axis. Between these two 

 extremes are numerous types of intermediate morphology, oval and pear- 

 shaped. On the assumption that the most primitive caulobacteria are those 

 which most closely resemble other bacteria, the terminal stalk and longitudinal 

 fission may have developed as an adaptation to sessile life. 



