122 Pla?it Biology 



Not all species are able to locomote in a liquid, but when they do, this 

 is accomplished by the rhythmic, vibratile actions of whiplike proto- 

 plasmic structures known as flagella (fla -jel' a) (L. flagellum, whip). 



Certain types of bacteria, like higher plants, require free atmospheric 

 oxygen for their normal activities and are known as aerobes (a'erobe) 

 (Gr. aer, air; bios, life). Other species do not require free oxygen but 

 secure it by breaking down certain types of oxygen-bearing foods through 

 the action of enzymes. These are known as anaerobes (ana' er obe) (Gr. 

 an, without; aer, air; bios, life). 



The various types of bacteria grow at different temperatures. Those 

 growing best at temperatures of 14° C. or below are known as psychro- 

 philes (si'krofil) (Gr. psychros, cold; philein, to love) and those having 

 an optimum temperature between 20° and 40° C. are mesophiles (mes' o- 

 fil) (Gr. me SOS, middle), while those that grow best above 45° C. are 

 called thermophiles (ther'mofil) (Gr. thermo, heat). 



Bacteria produce enzymes (en'zim) (Gr. en, in; zyme, leaven) with 

 which they perform various functions. Those which are active within 

 the cells (intracellular) are called endoenzymes, while those which are 

 secreted to the outside are called (extracellular) exoenzymes. 



Not all bacteria produce diseases; in fact, a great majority of them 

 do no harm, and a few species are actually beneficial. Pathogenic bac- 

 teria may produce diseases in other plants, in animals, and in man. 

 Bacteria reproduce asexually by fission in which the cell divides into two 

 parts. Frequently, after fission, the cells may remain together to form 

 a colony. Under favorable conditions fission may occur every twenty to 

 thirty minutes. Certain species produce resistant endospores by a con- 

 densation of the cell contents into a spherical or oval mass and the loss of 

 a certain amount of water (dehydration). A resistant spore wall sur- 

 rounds the spore (Fig. 34). A few species of bacteria may produce 

 within their cells a number of small bodies called gonidia (go -nid' i a) 

 (Gr. gone, "seed"; idion, small), each of which develops into a typical 

 bacterial cell. Certain species, especially the filamentous types, may 

 produce tiny conidia (ko-nid'ia) (Gr. konis, dust; idion, small) at the 

 tips of the filaments, similar to the formation of such structures by cer- 

 tain true fungi. 



Examples: Bacteria (various types of cocci, rods, spirals, and fila- 

 ments) (Fig. 34). 



7. Phylum Myxomycophyta (mik so mai -kof i ta) (Gr. myxos, slime; 

 mykeSj fungus; phyta, plants). — The slime molds (slime fungi) are 



