Simple Plants Without Chlorophyll — Fungi 171 



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

 The number and location of flagella vary with the species (Fig. 34), some 

 having a single flagellum, others having a tuft of flagella at one end, 

 others having tufts at each end, and still others having flagella over the 

 entire surface. 



Like other plants, bacteria produce enzymes with which they perform 

 various functions. Those which are active within cells are called (intra- 

 cellular) endoenzymes, while those which are secreted to the outside 

 are called (extracellular) exoenzymes. Bacterial enzymes digest foods 

 by converting complex, water-insoluble foods into simpler, water-soluble 

 types. Bacteria also synthesize enzymes which aff"ect processes of oxida- 

 tion and reduction and hence are influential in respiration. 



Probably when most persons think of bacteria they think of diseases. 

 However, of the total number of bacterial species, only a comparatively 

 small group produces diseases in animals and other plants. In fact, a 

 few species are actually beneficial, while a great majority are neither 

 harmful nor beneficial according to our present knowledge. Some of 

 the diseases produced by bacteria, yeasts, and fungi, as well as some of the 

 benefits, are discussed in the chapter on Economic Importance of Plants. 



Bacteria cause diseases in plants as illustrated by the following typical 

 examples: (1) soft rot of cabbage, carrot, cucumber, celery, etc., (2) 

 the wilt diseases of corn, tomatoes, potatoes, squash, melons, cucumbers, 

 etc., (3) the root rot of cotton, (4) fire blight of pears and apples, (5) 

 crown galls of apples, grapes, raspberries, alfalfa, etc., (5) bacterial blight 

 of beans, (6) bacterial blight of walnut, and many others. 



Bacteria may cause such diseases in animals as tuberculosis in cattle 

 and hogs, chicken cholera, pneumonia, septicemia in cattle, anthrax in 

 sheep, glanders in horses, goats, and sheep, botulism in chickens and 

 other animals, rat plague. Bang's disease (brucellosis or undulant fever) 

 in cattle, tularemia in rabbits, etc. 



Bacteria reproduce asexually by fission in which the cell divides into 

 two parts at right angles to the long axis (Fig. 34) . Mitosis is apparently 

 not utilized in the process, since no mitotic figures have been observed. 

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

 Each species forms a colony which has more or less constant character- 

 istics for that species and thus may be used for identifying them. Under 

 favorable conditions (proper food, moisture, temperature, etc.) fission 

 may occur every twenty to thirty minutes. At this rate of fission a single 

 bacterial cell in twenty-four hours would have nearly 5 million trillion 

 off"spring whose total weight would be many hundred tons. However, 



