156 THE CYTOLOGY AND LIFE-HISTORY OF BACTERIA 



are considered. Leaving aside diosc such as Bc<^iatoa, which arc ahnost 

 certainly not true bacteria, almost all autotrophs are either spirilla, vibrios, 

 pseudomonads or those colonial pseudomonads some oi which are classed as 

 chlamydobacteria. They must therefore be regarded as primitive, aquatic 

 forms ; which might reasonably be expected in any sound evolutionary 

 system. 



G: SUMMARY 



There exists morphological evidence which suggests that the bacteria have 

 evolved, in parallel with other groups of living organisms, from an aquatic to 

 a terrestrial mode ot lite. 



The most primitive bacteria arc the spirilla, which have characters inter- 

 mediate between those of typical bacteria and flagellates. 



The most highly evolved bacteria are terrestrial and have special mechanisms 

 for the aerial distribution o£ their resting stages. By the same criteria, the 

 autotrophic bacteria are relatively primitive in respect of their morphology, 

 as they appear to be in their physiology. 



The evolutionary significance of different types of flagellation and of the 

 bacterial endospore are discussed. 



BIBLIOGRAPHY 



(i) Beroi-y's Manual of Dctcriii'uiativc Bacteriolo^iy. 6th cd. (1948) London : Balliere, 

 Tindal & Cox. 



(2) BissET, K. A. (1950) Nature. 166. 431. 



(3) BissET, K. A. (1952) Bacteria. Edinburgh : Livingstone. 



(4) BissET, K. A. and Grace, J. B. (1954) Symposium : " Autotrophic Micro- 



organisms." Cambridge University Press. 

 {5) Grace, J. B. (1954) J. Gen. Microbiol. 9. 325. 



(6) Kluyver, A. J. and van Niel, C. B. (1936) Zbl. f Bakt. IL 94. 369. 



(7) PijPER, A. (1946)]. Path. Bact. 58. 325. 



(8) Prevot, a. R. (1933) Ann. Sci. Nat. Bot., Ser. 10. 15. 23. 



