CHAPTER TWENTY-FOUR 



THE 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 com- 

 plex plants of today have been derived ; that is, they believe 

 that the present-day plants were evolved from those that 

 existed on the earth in former times. Some of the simple 

 plants of the past still persist, and many plants of inter- 

 mediate degrees of complexity survive ; but during the de- 

 velopment of the plant world, new and increasingly complex 

 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 to- 

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

 modifications are going on now as in the past, and (3) that 

 the new plants of the future will be 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 foimd 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 

 intergrading species, (6) by the experience of plant breeders 

 and the history of our cultivated plants. 



The record of plants of the past. When a leaf falls from a 

 tree on soft mud, it may become imbedded in it. Later the 



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