30 



BACTERIA AND THEIR PLACE IN NATURE 



of plants is usually made up of cellulose or one of its derivatives; the 

 outer membrane of the animal cell is nitrogenous and where there 

 is a heavy cell wall it is chitinous. Both of these distinctions break 

 down in the case of the lower forms of plant and animal life. 



The "blue-green" alga?, or Schizophyceae, possess chlorophyll and 

 are obviously plants. Structurally, many of these are practically 

 identical with bacteria. This constitutes a strong argument for the 

 plant affinities of the bacteria. 



Nor is it an easy task to differentiate nicely between bacteria, 

 yeasts, and molds. Generally speaking, typical bacteria, yeasts, and 

 molds may be distinguished from each other as follows: Bacteria 

 are unicellular, devoid of a definite organized nucleus but con- 



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 tttttltt 



ttssssst 

 jssMisr 



FIG. 5. To illustrate the close relationship of the bacteria to the blue-green algye. 

 The figures to the left (.4) are blue-green algse, those to the right (B) bacteria. Those 

 forms most closely resembling each other are lettered alike. A, blue-green algae: 

 o, Aphanocapsa; b, Merismopedia; c, Gleotheca; d, Spirulina; e, Phormidium; /, 

 Nostoc. (All adapted from West.) B, bacteria: a, Micrococcus; b, Sarcina; c, 

 Bacillus; d, Spirillum; c, Bacillus in chains;/, Streptococcus. (Buchanan's Household 

 Bacteriology.) 



taining nuclear material. They multiply by transverse fission. At 

 times they are united into filaments or masses, but are usually 

 easily separated. Yeast cells are usually, though not always, larger 

 than bacteria. Although unicellular they contain a definite organ- 

 ized nucleus. They may remain united after cell division, but each 

 cell constitutes a definite entity. Most yeasts multiply by budding 

 -only a few by simple fission. Molds are multicellular, nucleated 

 organisms which are usually made up of a mass of interwoven or 

 radiating threads consisting of chains of cells. 



Divisions of Plant Kingdom. Plants are divided into four great 

 groups: Spermatophytes or seed plants, Pteridopkytes or fern plants, 

 Bryophytes or liver-worts and mosses, and ThaUophytes or thallus 

 plants. This last group has little or no differentiation of vegetative 



