550 General Botany 



corn was cultivated by the earliest races of men on the American 

 continents. When first found by the early explorers the Indians 

 not only had corn, but they were growing all of the subspecies 

 that we now distinguish as starchy, sweet, soft, waxy, flint, pod, 

 and pop corns. The wild species from which corn was derived 

 is unknown. Since the discovery of America some of these sub- 

 species have been greatly improved by crossing and selection. 



All the modern varieties of cultivated plants which supply 

 our fruits, flowers, roots, tubers, and fibers have resulted from 

 the activities of plant breeders. They are mutants selected 

 either from former wild plants or from previously grown varieties. 

 In many plants which cross-pollinate readily, the selection was 

 preceded by hybridization, which often produces plants with 

 new combinations of desirable characters. 



The experience of plant breeders furnishes abundant evidence 

 that plants produce mutants which differ in one or more char- 

 acters from their parents, and that these new characters are 

 heritable. These are the starting points of new varieties and 

 species. 



Plant breeding, then, has afforded us an opportunity to see 

 new varieties of plants evolve from older ones. The evolution 

 of many cultivated plants is a matter of historic record. There 

 is evidence that wild plants also produce mutants, and there is 

 every reason to believe that they have evolved in the same way. 



The fact of evolution conceded. The time has long since 

 passed when botanists have asked for further proofs of evolution. 

 Nevertheless, new evidences of evolution are appearing from day to 

 day in every field of botany, for the discovery of new facts about 

 the structure, physiology, or chemistry of plants frequently fur- 

 nishes important new proofs of evolution. We may say, then, 

 that the evolution of plants is a fact, not a theory. 



The method of evolution. While evolution may be considered 

 a fact, the methods and causes of evolution are still problems 

 upon which field observations, intensive laboratory study, and 



