LIFE HISTORIES OF FUNGI 287 
simplest plant structures known. They are one-celled, 
but of many shapes, and with or without motile cilia. 
They include the smallest living things known. There 
are even reasons for believing that some forms are ultra- 
microscopic, that is, too small to be seen with the most 
powerful microscopes that can be made. Some forms are 
less than one fifty-thousandth of an inch in diameter. 
Of some kinds of bacteria, as many as 300 could be placed 
side by side on the period at the end of this sentence. In 
fact the word "microbe" means "tiny living thing," 1 
though not all microbes are bacteria. The germ of 
malaria, for example, is a microscopic animal (protozoon), 
resembling an Amceba. 
Several genera of bacteria are distinguished according 
to shape as, for example, Bacterium (non-motile rods), 
Bacillus (motile rods), Micrococcus (spherical), Spirillum 
(spiral threads) (Fig. 211). 
FIG. 211 . Various forms of bacteria, a, Spirillum; b f Bacillus typhosus; 
c, Staphylococcus; d, e, j, h, Micrococcus; f, k, I, Bacillus; g, Pseudomonas 
pycocyanea; i, Streptococcus. 
They are found everywhere and multiply rapidly by 
cell-division, whence they are called "fission-fungi," or 
Schizomycetes. Not possessing chlorophyll, they are all, 
of course, either parasitic or saprophytic, some being 
highly beneficial in fact indispensable to man; others 
highly harmful, causing some of the worst known diseases 
of both plants and animals. 
1 From the Greek fwcp6y (mikros), small, + /9tos (bios), life. 
