90 A CENTURY OF PROGRESS IN THE NATURAL SCIENCES 



priate methodology, until the second half of the nineteenth century. Nevertheless, 

 some of the general features of the organisms, such as the occurrence of motile 

 forms, and multiplication by transverse fission, had been established, and the 

 discovery of the bacteria had raised the question whether they ought to be 

 regarded as plants or animals. 



Prior to 1854 their animal nature had been taken for granted, locomotion 

 probably being the chief criterion on which this belief was based. But in that 

 year Colin (1854) argued in favor of a close relationship with plants, especially 

 with the bluegreen algae. Following Nageli's introduction (1857) of the name 

 "Schizomycetes" (''fission fungi") it became customary to use this term, with 

 the ending appropriately modified to indicate the status as a family, order, or 

 class, for the collective designation of the bacteria. Along with this practice the 

 notion of the plantlike nature of the organisms gradually won ground. 



It cannot be denied that there are good reasons for subscribing to this view. 

 Especially the existence of an autotrophic mode of life among the bacteria may 

 be considered a strong point in its favor. The chemo-autotrophic sulfur bacteria 

 of the Beggiatoa-Thiothrix-Thioploca group in particular form a striking ex- 

 ample because also from a morphological-anatomical point of view they show 

 their plantlike nature; the structural similarity with the bluegreen algae of the 

 family Oscillatoriaceae is great indeed (Pringsheim, 1949). The green and purple 

 sulfur bacteria, and the brown and red nonsulfur bacteria resemble the plants 

 even more closely in physiological respect by virtue of their photosynthetic 

 ability. Recently it has been proposed that the chemo-autotrophic mode of life 

 can be envisaged as a precursor of the photosynthetic one, and that such processes 

 as characterize the photosynthetic bacteria would represent a logical link between 

 chemo-autotrophy and green plant photosynthesis (van Niel, 1949a). 



In spite of these rather compelling considerations, doubts as to the exclusively 

 plantlike nature of the bacteria have also been expressed, and this with increasing 

 frequency. It should be emphasized that Niigeli had not in the least committed 

 himself concerning the general relationships of his Schizomycetes ; this is evident 

 from the statement (Nageli, 1857, p. 760) : 



Ueber die Bedeutung der Gruppe Schizomycetes, ob es Pflanzen, Thiere, oder krank- 

 hafte thierische oder vegetabilisclie Elementartheile seien, dariiber giebt die anatomische 

 Struktur keinen Aufscliluss, dass es Pflanzen und keine Thiere sind, dafiir liegen wenig 

 Grijnde vor. 



The vast increase in our knowledge of "the bacteria" gained during the past cen- 

 tury has not made Nageli 's statement obsolete. This must in part be ascribed to 

 the difficulty of finding close affinities of certain bacteria with specific taxonomic 

 groups among the plants. While F. W. Andrewes, for example, states (1930, 

 p. 298) : 



... It was not till the middle of the nineteenth century that first Naegeli and then 

 Cohn proclaimed the vegetable nature of the bacteria. So gradual is the transition from 

 the mould-fungi, through the streptothrix group and the acid-fast bacteria, to ordinary 

 bacteria, that there are few who do not agree with Naegeli. 



it is equally true that relationships with bluegreen algae and with other groups 

 of organisms can also be defended on reasonable grounds. The quotation from 

 Prevot at the beginning of this section clearly reveals this difficulty. And from a 



