18 



REPRODUCTION 



not want to have decay or sour, as milk, fruits, meats, etc. 



The greatest harm done to man by these simple plants 

 and animals, however, is in the diseases they produce in 

 the human body or in the animals and plants that we 

 depend on. The most of our contagious and infectious 

 diseases, as tuberculosis, typhoid fever, yellow fever, 

 sleeping sickness, and scores of others are caused by 

 these one-celled organisms and the poisons they produce. 

 Similarly, diseases among hogs, cattle, horses, and 

 poultry; among garden vegetables, orchard fruits, and 

 flowers are caused by them. 



They do all this 

 damage in spite of 

 the minuteness and 

 small powers of a 

 single organism, 

 simply because they 

 can reproduce so 

 rapidly and effect- 

 ively. 



4. The Method of 

 Their Reproduction. 

 This is often just as 

 simple as can be. 

 When a bacterium 

 grows up to its full 

 size by taking food, 

 it may be a simple globe, or rod, or spiral, depending on 

 the kind. When this has taken place, the cell may at once 

 divide, by a partition through the middle, into two cells, 

 each having one-half the material and one-half the size of 

 the original cell. Each of these daughter cells then grows 

 up to the adult size, and repeats the process. In some 

 bacteria this growth and division may take place in less 

 than an hour. This rapid reproduction is possible because 

 the plant and the process are both so simple. Because of 

 the rapid growth and reproduction it comes about that in 



Figure 3. Various types of bacteria, much en- 

 larged. From Coulter s Plant Life attd Plant Uses. 



