198 



PLANTS AND MAN 



introduced into this country relatively recently; many varieties 

 (satsuma and Burbank) were developed by Luther Burbank after 

 hybridizing them with our native plums. The European plum is 

 still growing wild in its native Eurasia where it has been culti- 

 vated since the time of the Swiss lake dwellers and the Romans. 

 This is the best known of all the plums. Introduced into the 

 United States by the colonists, the European plum is now grown 

 on both the Pacific and Atlantic coasts and in the Great Lakes 

 region. Best known of the several hundred varieties which are its 

 descendants are the green gage and the lombard plums. A par- 

 ticularly valuable variety of the European plum is the prune, 



Fig. 135. — ^The ovary of a stone-fruit forms a fruit with two distinct regions, of 

 which the outer one is fleshy and edible as in the cherry. 



which has fruits with such a great sugar content that they can 

 be dried and cured without removing the stones. Prunes form 

 the second most valuable crop in California today. The plums 

 are gathered after they have fallen to the ground, and then dipped 

 in boiling water or lye, sun dried in racks and finally treated with 

 boiling water and glycerine or fruit juice to give them a glossy 

 surface as well as to sterilize the skin. California orchards totalling 

 over six million trees produce four hundred million pounds of 

 prunes annually. In addition to California, Jugoslavia and France 

 also grow a commercial prune crop. 



Although there are several common native species of cherry, 

 not one is of any horticultural value. Cultivated cherries are 

 derived from two species: the sweet cherry of Europe and Asia 

 Minor, and the sour cherry of Asia Minor. Sweet cherry trees are 



