CHAPTER VII 

 ENVIRONMENT AND ADAPTATION 



WHAT were the conditions prevailing upon 

 the earth when the first organisms ap- 

 peared, must remain purely conjectural. The earliest 

 forms of life have left no recognizable traces, and 

 the first unmistakable plant remains are so highly 

 organized as to make it certain that these must have 

 been preceded by a long series of simpler forms. 

 As we have already indicated there is some reason 

 to believe that the bacteria and blue-green algae 

 more nearly approach the primordial plants than 

 do any other living forms; but whether or not 

 these were the progenitors of the higher plants is 

 another question. The resistance of many of these 

 organisms to very high temperatures and other con- 

 ditions which are not favorable to the higher plants, 

 suggest that the conditions of life during the earliest 

 history of the plant kingdom were different from 

 those existing at present, but of course we can 

 only guess what these conditions were. 



The Higher Plants Derived from Algae. A study 

 of the evolution of the higher plants makes it al- 

 most certain that these are descended from green 



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