David Starr Jordan 



With many crosses of many things it is certain 

 that forms of great importance will come out 

 every year, though never in profusion. 



In developing a spineless cactus for stock-feed- 

 ding, selections were made from the three hard 

 northern species, Opuntia rafinesquii, O. mesacantha 

 and O. vulgaris, the latter the common prickly 

 pear; these were crossed with O. tuna, of South- 

 ern California, ficus indica, from Alba, Spain, and 

 with a small opuntia from Central America, almost 

 thornless. 



The cactus of all species has smooth cotyledons, 

 but the first bud is covered with thorns. These 

 thorns have also been eliminated by selecting the 

 smoothest individual seedlings without crossing. 

 Crossing in this case generally interrupts the 

 process, as it brings out well-fixed ancestral 

 traits, but later, to combine the best qualities of 

 several species, crossing and selection must be 

 resorted to. Examples seen were shoots of the 

 original stock, prickly; the second generation, 

 slightly prickly; the third, without thorns; and 



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