THE CACTUS 109 



with pollen from the stamens, lest the next pol- 

 lenizing be vitiated. 



Each blossom thus pollenized 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 botanist, and there is the greatest amount of 

 variability, so that no two botanists are agreed 

 as to the precise 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. 



For years collectors in all parts of the world 

 have gathered specimens for me, and, as knowl- 



