236 COLLEGE BOTANY 



Evolution. From our previous studies we have learned that 

 plants range from very small, simple organisms to very large, 

 complex organisms. Most of them are absolutely dependent on 

 sunlight for their existence, and all animal life is dependent on 

 plant life. Therefore, plants must have appeared on the earth 

 in advance of animal life. We have reason to believe that these 

 first forms .of plant life must have been very small and very 

 simple in structure ; in fact, they may have been simpler than 

 any species of plant in existence at this time. We have reason 

 to believe that other forms of plant life, possibly all forms, have 

 been derived from these first forms of life. To accomplish this 

 requires many changes through long periods of time. This 

 modification of plant life is known as " organic evolution." It 

 offers no satisfactory explanation as to the origin of the earth 

 or the source of life, but by the study of the laws of nature, it 

 attempts to explain the modification of plant and animal life 

 through the long geological ages. This theory of organic evolu- 

 tion is exactly the reverse of the theory of special creation. It 

 is a theory of gradual change and implies that the present forms 

 of life are different from the original forms. It emphasizes not 

 only the origin of life but the laws controlling life. 



Geological Record. Evolution is not restricted to living 

 things. The inorganic, as well as the organic, is subject to 

 great changes, due to the laws of nature. 



The earth has undergone many and wonderful changes since 

 its origin, and in fact these changes are going on at the present 

 time. Earthquakes and volcanoes bring sudden changes, but 

 water, frost, wind and other agencies are slowly but surely wear- 

 ing down the mountain ranges, filling the valleys and modifying 

 the face of the earth. What was once the surface mav now be 



