THE EVOLUTIONARY RELATIONSHIPS OF BACTERIA 1 47 



designed as a key, for identification purposes, rather than as a classification 

 proper. Litde or no attempt is made to relate the groups to one another, and 

 some oi these groups have been defined mainly upon physiological criteria 

 and are decidely heterogeneous morphologically. Bacteria are accorded the 

 status of a Class of Plants, the Schizotnycetes, and are defined in a most un- 

 satisfactory manner, by criteria which are either indifferent {c.{i. they can be 

 almost any shape), or negative, or demonstrably false, or both (c.i^'. they are 

 supposed to be devoid of a " definitely organised nucleus "). The sole 

 suggestion concerning the nature and relationships of bacteria is found in the 

 words : " the closely related blue-green algae " ; and since the blue-green 

 algae are the only major group in which flagella appear never to have existed, 

 whereas they are found in plants, animals, fungi and bacteria, the closeness of 

 this relationship is highly dubious. This misconception, which is of very 

 long standing, is buttressed by the inclusion among the bacteria, as listed by 

 Sergey's Manual, and especially among the autotrophic genera, of such 

 obvious blue-green algae as Beggiatoa, (see Bisset & Grace, 1954, for further 

 references). 



The attempt of Kluyver and van Niel (1936) to introduce into bacterial 

 systematics the element of evolutionary relationship which is the foundation 

 of such systems in other sciences was an obvious reaction against the amorphous 

 compilations which had previously been available. Their diagram of supposed 

 evolutionary trends has proved exceedingly popular, and has frequently been 

 reproduced. But, in the opinion of the present writer, certain defects, both 

 in their argument and in their information, render their theories unacceptable. 



The basic assumption of Kluyver and van Niel was that the coccal forms 

 have the simplest morphology, and may thus be considered ancestral to all 

 other bacteria. However, the evidence produced in the earlier chapters of 

 this book indicates that the cocci are not a morphologically homogeneous 

 group, and that most of them have a complex, septate structure, characteristic 

 of the Gram-positive bacilli, to which they appear to be closely related. Ol 

 the Gram-negative cocci, some are degenerate, parasitic representatives of the 

 Gram-positive genera, others may be derived independently from the 



