342 



THALLOPHYTES 



Many of the Bacteria are provided with cilia or terminal flagella, 

 which enable them to move about independently. The ciUa are 

 distributed over the body in various ways and are extremely 

 difficult to detect. Some of the motile forms are quite active 



and motiUty is one of the fea- 

 tures suggesting that Bacteria 

 are animals. Their cell walls 

 are more or less slimy, and their 

 protoplasm is not definitely or- 

 ganized into nucleus and cyto- 

 plasm. These features with 

 their power of resistance suggest 

 a relationship with the Blue- 

 green Algae. They possess no 

 chlorophyll and are almost ex- 

 clusively parasites or sapro- 

 phytes. The ability of the 

 protoplasm to endure extreme 

 cold, high temperatures, and 

 drying even surpasses that of 

 the Blue-green Algae. Besides 

 remaining separate or forming 

 filaments, Bacteria commonly have another stage in which numer- 

 ous individuals are held together in masses or colonies by a matrix 

 of gelatinous substance formed from their walls. This stage 

 is known as the zoogloea stage {Fig. 296). These colonies form 

 the characteristic pellicles on nutrient media, as on the water in 

 which hay. Beans, Peas, or other organic substances are decay- 

 ing, and on bouillon and various solid media {Fig. 297). When 

 food is scarce or other conditions unfavorable, some forms shrink 

 their protoplasm and enclose it in an inner heavy wall, thus form- 

 ing what is called a spore. Enclosed in this heavy wall, they are 

 inactive and extremely resistant to cold, heat, and drying. When 

 transferred by wind or other agents to a suitable medium, they 

 shed the'Tieavy wall and become active again. 



Their method of getting food is essentially the same as in the 

 Myxomycetes. Since they live on or within the food supply, 

 they are ia direct contact with the food material, and have only 

 to change it to a soluble form and absorb it through their walls. 

 They secrete enzymes which change insoluble foods to soluble 



Fig. 295. — Some forms of Bac- 

 teria. At the right and above, a 

 coccus form; a bacillus just below; 

 and a spirillum form at the bottom. 

 At the left, above, a chain of bacilli; 

 and, below, bacteria in the spore 

 stage. Very highly magnified. 



