82 HEREDITY AND EVOLUTION IN PLANTS 



originated by regressive evolution, their simplification 

 being closely correlated with a reversion from dry land to 

 an aquatic habit of life. A similar reduction of structure 

 is found in the tiny floating ferns, Sahinia and Azolla. 



71. Inorganic Evolution. — The process of evolution is 

 not confined to living things, but, as indicated above, 

 applies to all nature. Even the chemical elements are 

 believed to have been produced by evolutionary changes, 

 and to be even now in process of evolution. This is one 

 of the results of the recently discovered phenomenon of 

 radioactivity, which is essentially the transformation of 

 the atoms of one chemical element into those of another. 

 Fossil remains of marine animals and plants, found im- 

 bedded in the rocks on mountain summits, indicate, with- 

 out possibility of reasonable doubt, that what is now 

 mountain top was formerly ocean bottom. The mountain 

 has come to be, by a series of gradual changes. Rivers 

 and valleys are constantly changing so that the present 

 landscape is the result of evolutionary processes ; climates 

 have changed, as we know from the fact that fossil re- 

 mains of tropical plants are now found in the rocks in 

 arctic regions; the atmosphere and the water of the ocean 

 have reached their present condition as the result of gradual 

 transformations extending over aeons of time; even the 

 stars and planets, like our own earth, are coming gradually 

 into being, undergoing changes of surface and interior 

 condition, and ceasing to exist. Nothing is constant except 

 constant change. The main problem of astronomy is to 

 ascertain and record, in order, the evolutionary changes 

 that have resulted in the present system of suns and 

 planets. The main problem of geology is to ascertain and 

 record, in order, the evolutionary steps that have resulted 

 in the present condition of the earth. 



