654 General and Applied Biology 



may require a complete readjustment in a certain community. In fact, 

 these constant changes in the living world communities result in what 

 is called a succession of living organisms. When environmental factors 

 change sufficiently, the plants and animals which originally lived there 

 may be destroyed and their places taken by other types. Such a sequence 

 of plant and animal replacements is a succession which may occur natu- 

 rally or be brought about, at least in part, by artificial means. For 

 example, a fresh-water pond may have a certain type of animal and 

 plant population. When this pond dries, the resulting changes in the 

 environmental factors may result in a succession somewhat as follows: 

 animals and plants which require a great amount of water will be gradu- 

 ally replaced by those whose water requirements are not so great; as 

 the pond develops into a swamp, plants and animals typical of swamps 

 will succeed; herbaceous plants will appear, to be followed by various 

 types of shrubs, and eventually a succession of trees which will range 

 from poplars to oaks and hickories to beech and maples. Even the ap- 

 pearance of these trees show a typical succession of species, each follow- 

 ing the other as the proper environmental factors present themselves. 

 The same phenomenon of succession is to be noticed in the replacement 

 of plants and animals in an original forest community which was burned. 

 As diflferent plants succeed one another as environments change, so the 

 animal population will also undergo a succession in that area. Certain 

 types of animals requiring specific kinds of plants for protection and food 

 cannot reappear in the burned area until the proper plants have reap- 

 peared in the plant succession. These and many other similar phe- 

 nomena prove the unity and interdependence in the living world. 



E. Dependence of All Living Animals and Most Plants on Photosyn- 

 thesis 



All plants and animals require foods of some type or another. Since 

 animals and plants without chlorophyll cannot manufacture food, it is 

 apparent that in the final analysis all life depends, directly or indirectly, 

 upon the photosynthetic process for food. It is true that certain ani- 

 mals eat other animals, but somewhere in the continuous chain of food 

 supply the animal was dependent upon plants for food. Even the plants 

 without chlorophyll, such as fungi, bacteria, etc., must depend, directly 

 or indirectly, upon the process of photosynthesis for their source of food. 

 Bacteria mav live on an animal which has eaten another animal, but 

 probably the latter had consumed food which was manufactured by the 



