CHAPTER XXVI 



THE HISTORY OF PLANTS 



In this and following chapters we shall try to summarize what is known 

 of the course of evolution from earliest times to the present. In so doing 

 we encounter the historian's difficulty of selecting what is most significant 

 without distorting and oversimplifying the story. Actually there are 

 great gaps in our knowledge of the life of the past, and the fossils them- 

 selves are often hard to interpret. Nevertheless the general course of 

 evolution is plain to be read in the rocks. In our brief account we shall 

 have to make broad statements that are not without their exceptions, to 

 omit all mention of many interesting and important matters, and to 

 depend upon selected examples to illustrate what went on in all groups of 

 organisms. 



The story of evolution cannot be told without naming its characters. 

 The names will be meaningless if they do not call to mind something of 

 the appearance, structure, habits, and systematic position of the animals 

 and plants to which they refer. All of the organisms discussed are included 

 in the Appendix, where they are arranged in taxonomic order with brief 

 descriptions of their most important characteristics. 



THE BEGINNINGS OF LIFE 



Our planet was born from the sun, along with the rest of the solar 

 system, perhaps 2,500 million years ago. Nearly all authorities agree that 

 the earth must have passed through a molten stage during which its 

 internal constitution was established. We do not know how long it took 

 for the earth to cool and solidify, for its deep and heavy atmosphere to 

 thin by condensation of the water into the oceans, and for sunny skies 

 and running water to usher in the reign of uniformity. 



We do not and probably never shall know just how or when life ap- 

 peared upon earth; but we can at least deduce something of the conditions 

 and steps that led to the development of protoplasm. Organic substances 

 must have existed in the first water that condensed around the cooling 

 earth, for carbides, from the molten interior, interacting with the super- 

 heated steam of the atmosphere, would have produced a variety of car- 

 bon-containing compounds. These, dissolved in the envelope of hot water 



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