Ch. X] THE BACTERIA 409 



consequences to man or other organisms, the significance of 

 their actions is always the same to the Bacteria themselves. 

 When they break up the chemically complex organic sub- 

 stances on which they live, and draw therefrom the materials 

 they need in their own growth and respiration, the remnants 

 of those substances fall naturally, according to chemical 

 affinities, into diverse materials, which, together with the 

 excretions of the Bacteria themselves, happen to have 

 properties injurious or beneficial, offensive or agreeable, 

 to other organisms, including mankind. The details depend 

 partly upon the Bacteria, and partly on the nature of the 

 substances concerned. 



Ecologically the Bacteria are typical parasites and sapro- 

 phytes. Phylogenetically, their simplicity of structure, 

 reproduction only by division, formation of gelatinous colo- 

 nies, and ability to withstand extreme conditions, relate 

 them very obviously to 

 the Cyanophyceae, of which 

 they seem to represent a 

 specialized offshoot. On 

 the other hand, the Bac- 

 teria are simpler than the 

 Cyanophyceae in some fea- 

 tureswhich appear primitive 

 rather than degenerative, 

 notably, the retention of 

 physiological individuality Fm 279 _ ChondromyCQS eneaiu9t a 



in the individual Cells rather typical form of Myxobacteriaceaj ; X 50. 

 than the Colony, and the The structure is a colony in which 

 " l t the very minute individual Bacteria 



chemosynthetic habit of are embedded in gelatinous material. 

 Some Of their members. They form spores in the terminal heada 



or cysts. (From Thaxter.) 



These facts suggest that 



the Bacteria may have preceded the Cyanophyceae in time, 

 developing from chemosynthetic forms which lived prior to 

 the development of phycocyanin or chlorophyll. 



While the Bacteria proper exhibit colonial development 



