THALLOPHYTA 305 
Cell structure. The bacteria are usually divided into three 
groups, according to their shape: coccus forms, which are 
spherical cells; bacillus forms, rod-shaped cells; and spirillum 
forms, curved cells (Fig. 308). 
The bacteria are small masses of protoplasm without chloro- 
phyll and surrounded by cell walls. A few of the cocci and 

Fic. 308. Various forms of bacteria 
First line, at the left, coccus forms; at the right, bacillus forms; second and 
third lines, bacillus forms; fourth line, spirillum forms; fifth line, stages in 
formation of an endospore 
many of the bacilli and spirilla have very small, delicate, 
threadlike processes known as flagella (Fig. 308). The move- 
ments of these flagella give the bacteria the power of locomotion. 
The bacteria do not possess nuclei such as are found in 
higher plants, but many of them contain granules which have 
staining properties resembling those of chromatin (Fig. 309). In 
many cases these granules are scattered throughout the cell, 
while single spherical, spiral, or zigzag structures have been 
described in some bacteria. The question as to whether or not 
