CHAPTER I. 

 BACTERIA. 



Definition. Bacteria (from the Greek fiaxTypiov, a rod) are 

 minute unicellular organisms, now generally conceded to 

 belong to the vegetable kingdom and classed among the 

 lowest thallophytes. 



Classification of Bacteria. The bacteria were thought 

 by Leeuwenhoek and his successors, even to the time of 

 Bhrenberg and Dujardin, to be animalcules belonging to 

 the infusoria, and were in consequence placed in the animal 

 kingdom. With our present knowledge they can unhesi- 

 tatingly be placed in the vegetable kingdom, among the 

 lower orders of the flowerless plants. The flowerless plants 

 or Cryptogamia include the Pteridophyta; the Bryophytce, 

 including the ferns and liverworts; and the T hallo phy tee, 

 including the algcz and fungi. It is among the Thallophytae, 

 and probably among the fungi, that bacteria belong. 



The algae differ from the fungi in possessing chlorophyl, 

 and as the bacteria sometimes contain .chlorophyl, it be- 

 comes a question whether they should be included in either 

 of these groups or form a group by themselves; and their 

 classification among the fungi is held by botanists to be 

 provisional. 



The scientific grouping of the bacteria themselves has not 

 yet been achieved, the best characters to be used as the basis 

 of classification being undecided. The best system for their 

 provisional arrangement is probably that of Migula,* or the 

 modification of it suggested by F. D. Chester, f in which the 

 morphology, sporulation, and appendages of the bacteria 

 all enter as important features. 



* "System der Bakterien," Jena, 1897-1900 (vols. I and n appearing 

 at different times). 



t " Preliminary Arrangement of the Species of the Genus Bacterium," 

 "Ninth Annual Report of the Delaware College Agricultural Experi- 

 ment Station," 1897; Newark, Delaware, U. S. A. 



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