CHAPTER XXIII 

 THE SMALLEST PLANTS (BAOTEEIA) 



241. Bacteria. — Bacteria are the smallest of all plants 

 and can be seen singly only through the aid of a powerful 

 microscope. We do not know all about their life pro- 

 cesses, but we have learned much about their effect. 

 We constantly hear about these plants, cither under their 

 correct name, bacteria, or under the names of germs <>r 

 microbes. Two incorrect ideas concern- 

 ing bacteria are prevalent, — one, that 

 bacteria are animals, and the other, that 

 all of them are harmful. It is definitely 

 known that bacteria are plants ; that 

 small as they are, they are among the 

 most important plants in the world ; that 

 most of them are helpful, and only a FlG 



few harmful. They are, however, so 



much like the one-celled animals (protozoa) that the 



word germ is not unnaturally used to cover both. 



242. Shape and Size of Bacteria. — Bacteria, according to 

 their shape, are grouped into three classes: (1) round 

 (the cocci); (2) rod-shaped, like an unsharpened pencil 

 (the bacilli); (3) those that are shaped like a corkscrew 

 (the spirilla). Most of the names for the different bacteria 

 contain one or another of these words, thus indicating the 

 shape of the bacterium 1 under discussion. The spirilla 

 and the bacilli often have on one or both ends tiny thread- 



1 Bacterium, singular of bacteria. 

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