262 BREEDING CROP PLANTS 



varieties gave good results when introduced into the United 

 States, the breeding of apples has not been seriously undertaken 

 until comparatively recent times. The cultivated varieties are 

 very numerous. Our pears were developed from two very dif- 

 ferent wild species, Pyrus communis, the wild pear of western 

 Asia and Europe and the hard, gritty sand pear of northern China. 

 P. communis is the source of our eating pears, such as the 

 Bartlett, while inter-species crosses furnished our cooking and 

 winter pears. 



Peaches were first developed in China. When one compares 

 the little hard, bitter wild peach of China and our cultivated 

 varieties the results of early breeding are strikingly illustrated. 



There are three groups which are commonly accepted as the 

 ancestral forms of our cultivated plums: (1) The thorny wild 

 European species which produces dark purple fruits about the 

 size of a pea. These are the source of our prune varieties. (2) 

 North American native wild plums which have a very juicy 

 flesh without much meat. Several species are recognized 

 (Wight, 1915). (3) A Chinese-Japanese wild species. Many of 

 the cultivated varieties of plums are largely of hybrid origin. 



There are over 120 wild species of cherries which are native to 

 Asia and from 200 to 1,500 wild species of raspberries and black- 

 berries. The variation in type of the wild red raspberries of 

 New England is a good illustration of a wide diversity of forms. 

 Some of these are probably results of crosses with escaped culti- 

 vated varieties. Natural hybridization certainly played a large 

 part in the evolution of such fruits and the selection of promis- 

 ing wild seedlings furnished the major part of our cultivated 

 varieties. 



Fletcher (1916) has described 1879 varieties of strawberries 

 which originated in North America and 26 European varieties 

 which have attained prominence in this country. The straw- 

 berry is largely a hybrid product of four or more species. 



The citrus fruits are all of Asiatic origin. Present cultivated 

 varieties have for the most part been produced during the last 

 100 years. The grapefruit industry of the United States has 

 been developed in the last 25 years. This fruit, which is a native 

 of islands lying to the south of Asia, was introduced into the West 

 Indies early in the eighteenth century and more recently from 

 the West Indies into Florida. Table LXVI1, which is part of a table 

 published by White (1916), is a summary statement of the source 



