BACTERIA AND THEIR ROLE IN NATURE 13 



known the terms plants and animals were invented to distinguish 

 familiar living objects such as elephants and trees, insects and 

 mosses. Even today we may find one scientist classifying an 

 organism as a plant, whereas another worker may classify it as 

 an animal. However, it is impossible to lay down hard and fast 



tSIt St tS^ 

 SSttSttI 



ittftitt 







Fig. 3.^ — ^To illustrate the close relationship of the bacteria to the blue-green 

 algae. The iigures to the left (A) are blue-green algx, those to the 

 right (B) bacteria. Those forms most closely resembling each other are 

 lettered alike. 



A, blue-green algJE. a, Aphanocapsa. ^, Merisraopedia. Cj Gleotheca, d, 

 Spirulina. e, Phormidium. /, Nostoc. (All adapted from West.) 



B, bacteria, a, Micrococcus. I, Sarcma. c, Bacillus, d. Spirillum, e, 

 Bacillus in chains. /, Streptococcus. (After Buchanan ) 



rules which distinguish some microscopic plants from microscopic 

 animals. At least one scientist has suggested that to obviate this 

 difficulty we create a new kingdom, the Protista, into which we 

 place all such doubtful species. This only brings more difficulty 

 as it becomes necessary to draw two lines of demarcation in 

 place of one. 



This has led to the peculiar predicament of students saying that 

 some animals are plants in the botanical department, but on being 

 transferred to the zoological department they have become ani- 

 mals again. 



There are four great divisions of the plant kingdom: the seed 

 plants or Spermatophytes, fern plants or Pteridophytes, mosses or 



