162 LUTHER BURBANK 



to depart from the spine-bearing custom of their 

 race. Among the seedlings of these plants some 

 were found to be much less spiny than others, 

 and it was ultimately possible, by selecting 

 among literal millions of specimens, to develop 

 races absolutely devoid of spines and spicules, 

 as we have seen. 



It would not have been unreasonable, perhaps, 

 to expect that the spineless races thus developed 

 would breed true to spinelessness ; particularly 

 when we recall that the thornless blackberry, 

 if inbred, produces only thornless progeny. But 

 if such an expectation were entertained, it would 

 be doomed to disappointment, for the spineless 

 cactus does not breed true. In point of fact, 

 there may be found among the seedlings of a 

 spineless variety plants that fairly bristle with 

 spines, rivaling in this regard the best protected 

 of their wild ancestors. 



Obviously, then, the condition of spineless- 

 ness in the cactus has quite different relations in 

 the scheme of heredity from the conditions that 

 govern spinelessness in the blackberry. In the 

 latter case, as we have seen, the spineless condi- 

 tion appears to be recessive, and the thornless 

 individual is as free from tendency to produce 

 thorns as if its entire coterie of ancestors had 

 been perfectly smooth-stemmed. The individual 



