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, ''^ 

 though not all microbes are bacteria. The germ of 

 malaria, for example, is a microscopic animal (protozoon), 

 resembling an Amesba. 



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, 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. 



^ From the Greek ixiKpSs (mikros), small, + /3/os (bios), life. 



