CHAPTER XXIII 

 PLANT BREEDING 



372. What Plant Breeding Is. As we have seen, the 

 varieties of Indian corn are numbered by hundreds ; and 

 there are many varieties of potatoes, apples, roses, and indeed 

 of most of our cultivated plants. Most of these varieties have 

 arisen since the plants in question have been in cultivation. 

 All the varieties of Indian corn, for example, are probably 

 descended from a single wild species, and the great majority 

 of them have appeared since corn began to be cultivated by 

 white men. All the varieties of potatoes probably came 

 from a single species, and all the apples (including the crabs) 

 from three species. Some varieties of cultivated plants 

 originated without anyone's knowing exactly when they ap- 

 peared or where they came from ; but most of them have de- 

 veloped because some of the men who were growing plants 

 tried to obtain varieties that would better serve their needs. 

 The improvement of old sorts of plants or the development 

 of new sorts is plant breeding. The few varieties of corn that 

 were cultivated by the American Indians when white men 

 first came to the continent had probably developed and been 

 preserved quite accidentally ; but most of the varieties that 

 have appeared since have been the result of more or less 

 systematic breeding. 



The development of varieties of cultivated plants is similar 

 in many respects to the development of varieties and species 

 among plants that are growing wild. Just as the many cul- 

 tivated varieties of potatoes are descended from a single 

 wild species of Solanum, so that and all the other species of the 

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