PLANT BREEDING 431 



trifoliate orange, which resists our winters as far north as Phila- 

 delphia, but bears a small, bitter, worthless fruit, was hybridized 

 with the common sweet orange. Three valuable hardy hybrids 

 known as citranges were produced. One of them makes a good 

 substitute for grape fruit, another for lemons, and the third for 

 rather sour oranges. They may be grown from two hundred 

 to four hundred miles farther north than ordinary oranges. 



Another citrous hybrid is that between the tangerine and 

 the grapefruit. This is called the tangelo, and has character- 

 istics somewhat intermediate between those of the parent spe- 

 cies. It is smaller in size, and the pulp is less bitter and acid 

 than that of the grapefruit, while the " kid-glove " skin, readily 

 peeled off with the fingers, is like that of the tangerine. 



Our most valuable citrous fruit is the Washington navel 

 orange, nearly or quite seedless. It originated from chance 

 seedlings found in a swamp along the Amazon and brought 

 from Bahia, Brazil, to the United States Department of Agri- 

 culture in the early seventies. This orange forms by far the 

 greater portion of the entire California crop of over 10,000,- 

 000 boxes a year. 



396. Results of hybridizing ornamental flowers. Some of 

 the most showy flowers of our gardens and greenhouses are 

 hybrids. Among the most important examples are the gen- 

 era Canna, Amaryllis, and G-ladiolus. Orchids, too, have been 

 hybridized to such an extent that a dictionary of hybrid 

 orchids has been prepared. 



In most cases of flowers which have been bred and hybrid- 

 ized for many years, the process of improvement has been due 

 partly to crossing and partly to selection. It is often impos- 

 sible to find out how many parent species or varieties have 

 entered into the production of the final hybrid. 



397. Summary of methods and results. Successful plant 

 breeding requires a continuous effort to get better plants, 

 either by picking out and growing chance varieties, or by con- 

 tinued selection, first of a set of choice parent plants, then 

 of their best offspring, and so on for several generations. 



