FORM AND STRUCTURE OF MICROBES 63 



bacteria, the Streptothriceae, which, by their filamentous and 

 branching appearance, form a link between the bacteria and 

 the simplest fungi. On the other hand, there are yeasts which 

 resemble bacteria in producing endospores and multiplying by 

 division instead of by budding. 



It is, however, with certain algae, the Cyanophyceae or blue 

 algae that the relationship is most marked. The Cyanophyceae 

 reproduce by division, presenting different shapes, long, 

 round, and curved, resembling cocci, coccobacilli and bacilli. 

 They are pleo- 

 morphic like the 

 bacteria. They 

 possess chloro- 

 phyll in contrast 

 to the bacteria, 

 but the pigment 

 which the Cyano- 

 phyceae possess 

 in addition to 

 their chloro- 

 phyll, the phyco- 



chrome (most often greenish-blue, soluble in water and 

 diffused throughout the cell) is not without some analogy to 

 the pigment of certain bacteria. Certain algae clump together 

 in mucilaginous sheaths resembling the zoogloea of certain 

 bacteria. The Cyanophyceae do not form endospores but have 

 arthrospores like some bacteria. There are species like 

 Beggiatoa^ in which it is far from certain whether they should 

 be classed with the bacteria or with the Cyanophyceae. These 

 analogies are so striking that a family, the Bacteriacecz, has been 

 made for the algae which border on the Cyanophycecz. 



But in view of the differences which exist between these two 

 families and the similarities which link up the bacteria and the 

 fungi (moulds and yeasts), certain authorities make of the 

 bacteria a heteroclitous group where there are brought together 

 representatives more or less altered or degenerated of various 

 lower plants. There exist no doubt bacterio-algae ; there are 



FIG. 29. Streptothrix. Branching bacteria. 



