CHAPTER FIFTY 



EVOLUTION OF PLANTS 



Those who have studied plants most have been led to the 

 conclusion that simple plants lived first on the earth, and that 

 from these simple forms all the varied and highly complex plants 

 of today have been derived ; that is, that the present-day plants 

 were evolved from simpler plants that existed on the earth in 

 former times. Some of the simple plants of the past still persist, 

 and many plants of intermediate degrees of complexity survive ; 

 but during the long period of geological time, new and increas- 

 ingly complex plant forms have been produced, and these higher 

 forms now dominate the vegetation of the earth. The process 

 by which the plants of today have come from the plants of the 

 past is called evolution (Latin : evolutio, an unrolling) . Evolu- 

 tion, with regard to plants, implies (i) that the plants of today 

 are the modified descendants of earlier forms, (2) that modifica- 

 tions are going on now as in the past, and (3) that there will be 

 new plants in the future, evolved from plants now living through 

 modification of present plant forms. 



The proofs of evolution in plants have been gathered from 

 many sources by many different students. These proofs include 

 the evidence furnished (i) by plant remains found in rocks and 

 coal, (2) by the distribution of plants on the earth's surface, 

 (3) by the remarkable similarity of organs, tissues, and cells 

 among the thousands of plants now in existence, (4) by the 

 similarity in the life histories of all plants, (5) by intergrad- 

 ing species, (6) by the experience of plant breeders and the his- 

 tory of our cultivated plants, and (7) by the discovery of new 

 mutants from time to time. 



The geological record. The earliest rocks (Precambrian) 

 contain few recognizable plant fossils, not because plants were 

 rare when these rocks were laid down, but because the rocks dur- 

 ing the long subsequent history of the earth were acted upon by 



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