LUTHER BURBANK 



the forms of vegetable life that have been intro- 

 duced, or improved, for the service of man within 

 the historical period. 



THE HEREDITY OF SPINELESSNESS 



Before taking leave of the spineless cactus, it 

 may be of interest to make further inquiry as to 

 the hereditary bearings of the condition of spine- 

 lessness. 



We have seen that the new spineless opuntias 

 were developed by a long series of experiments in 

 hybridizing and selection, in which use was made 

 of individuals that showed a propensity to depart 

 from the spine-bearing custom of their race. 

 Among the seedlings of these plants, some were 

 found to be much less spiney 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 cac- 

 tus 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, rival- 



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