APPLICATIONS OF PRINCIPLES OF HEREDITY 453 



new varieties of organisms without limit, having almost any 

 combinations of useful or fancy characters that he may desire. 

 This does not mean that new characters are produced by 

 these methods. When Burbank produced a "white black- 

 berry " he did not get a plant with a new character, in the 



FIG. 242. Spineless cactus (Opuntia) 



This variety was established by Luther Burbank through experimentation. It grows in 



arid soil that is otherwise useless, and promises to become a valuable fodder for horses 



and cattle. (From photograph lent by Mr. Burbank) 



biological sense. He combined a plant -having pale yellow 

 berries, of no value as fruit, with one having large, black 

 berries, the Lawton blackberry. From the hybrids he was 

 able to select for segregation and for ultimate fixation the indi- 

 viduals that combined pure lack of pigment with some of the 

 other desirable qualities. Another new creation of Burbank's 

 is the spineless cactus (see Fig. 242). 



Many of the new varieties of plants are hybrids that are incapable 

 of breeding true. These plants are propagated by means of cuttings or 



