THE FUNGI 



251 



certain of the lower groups of fungi, although neither the rela- 

 tionship of the bacteria nor their classification into definite 

 groups is as yet understood even by specialists in bacteriology. 

 Bacteria are usually grouped, for convenience, under certain 

 form types, illustrated in Fig. 134. 



Structure. The cells of the bacteria are the smallest of which 

 we have any definite knowledge, ranging from ^Q^ to -g^^-Q of 



Fig. 134. Form types of bacteria 



a, types of bacilli ; 6, types of micrococci ; c, types of spirilla. After Williams. Redrawn 

 from Marshall's "Microbiology" 



an inch in diameter. The rod bacteria, represented in Fig. 134, 

 a and c, vary from ^^-fr to g-Q-J--^^ of an inch in length. 



The bacterial cell differs somewhat from the ordinary plant 

 cell in the structure of the cell wall, in the chemical nature of 

 its protoplasm, and in the nature of the nucleus. The cell wall 

 is composed of two membranes, the outer of which may be- 

 come gelatinous, thus enabling the cells to adhere and form 

 simple colonies. 



The protoplasm is dense and contains more nitrogen than 

 that of ordinary plant cells. The nucleus, if present, has no 

 nuclear membrane, and some bacteriologists deny the presence 

 of a nucleus in the cells of bacteria, while others claim to have 



