LUTHER BURBANK 



brush over the receptive stigma, being careful not 

 to allow the brush to become smeared with pollen 

 from the stamen, lest the next poUenizing be 

 vitiated. 



Each blossom thus poUenized is of course 

 tagged to make permanent record of the cross, in 

 accordance with the method detailed in an earlier 

 chapter. 



It was customary, wherever possible, to make 

 the cross reciprocal, although with the Opuntias 

 as with other plants, it appears to make little if 

 any difference as to which is the staminate and 

 which the pistillate parent. Here as elsewhere in 

 the plant world the factors of heredity appear as a 

 rule to be distributed impartially between pollen 

 grains and ovules. 



The cactus plants that served as material for 

 my comprehensive experiments aiming at the 

 development of a spineless race of economic value 

 were very numerous as to species and very widely 

 diversified as to form and habit. More than one 

 thousand species of cactus are listed by the botan- 

 ist, and there is the greatest amount of variability, 

 so that no two botanists are agreed as to the pre- 

 cise classification of all the forms. 



Of course I have not had every species of cactus 

 at my disposal, but the number with which I have 

 worked is very large indeed. 



[186] 



