SAPROPHYTES 399 



ditions of the culture are most favorable for it. This type of 

 organism gradually consumes the food available to it and at 

 the same time contributes harmful waste materials to the 

 culture. When this continues for a time, the conditions of the 

 culture become gradually more unfavorable for this original 

 form, but at the same time it becomes more favorable for a 

 succeeding form of life. This succeeding form then becomes 

 the leading type in the culture for a time and then, in its turn, 

 in the same way, and for the same reasons, gives way to a new 

 successor. 



Now, if you can imagine, not one line of succession like this, 

 but many such lines going on at the same time, you will have 

 a fairly accurate picture of what is going on in your culture. 

 Not only this, but this picture of change in your culture is 

 a fairly accurate representation of what is going on in nature 

 everywhere where plant and animal matter are being changed 

 back to the simple inorganic compounds for which the green 

 plants originally built them up. 



453. Decay in General. It is a long and interesting story 

 from the planting of an acorn to the final dissolution by natural 

 processes of the body of the giant oak that results. One 

 might think that the story is ended when the tree has come 

 to its death, but with this picture of your culture in mind you 

 will see that probably the most interesting part of the story 

 begins with the death of the tree. Thousands of different 

 forms of life take part in its destruction and all bear perfectly 

 definite but extremely complex relations to each other. It is 

 in this work of the dissolution of organic bodies that micro- 

 organisms play their most important role in the life of the 

 earth. Were it not for the work that these organisms do, the 

 earth would become strewn with the dead bodies of animals 

 and plants, and the chemical elements which composed these 

 bodies would never again become available for succeeding 

 forms of life. 



454. Forms of Bacteria. As you study your culture from 

 time to time, you will have opportunity to observe the three 



