CHAPTER XI 



THE EVOLUTION OF PLANTS 



Since plants are autotrophic, that is, are capable of building 

 up their organic food from simple inorganic substances, and 

 since animals are allotrophic (heterotro])hic), or feed on the 

 organic compounds that plants have elaborated, it follows 

 that animals probably originated later than plants. We hope, 

 in succeeding pages, to demonstrate this, and to show further 

 that the simpler animals evolved as offshoots from colorless 

 bacterial lines of plant organization, through the slow acquisi- 

 tion by the. former of certain characters that now cause us to 

 distinguish them as animals rather than plants. 



If such be the biological relationship, it becomes necessary 

 to determine, if possible, the environal surroundings of primi- 

 tive plants and animals, the period approximately when they 

 first api^eared, how far traces of ancient organisms have been 

 preserved in the fossilized state, whether very ancient types 

 have survived long and checkered changes so as to exist still 

 in a condition little if at all altered from their primitive state, 

 and what the main lines of evolutionary advance have been 

 for those plants and animals that underwent progressive evo- 

 lutionary modification. These questions A\ill be considered 

 in the succeeding chapters. 



We believe all will agree that ijrimitive organisms were 

 soft unicellular, or later multicellular, types which would 

 leave no trace of their existence in the earth's crust. During 

 the slow but gradual evolution therefore of the soft algoid, 

 fungoid, and moss-like forms of plants, as well as of non-calci- 

 fied or non-silicified animals, many species, genera, and even 

 families may have arisen of which no record exists. 



15ut, as alread}^ stated (j). 53), in the most ])rimitive strati- 

 fied archfcan or proterozoic rocks, extensive beds of limestone, 



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