THE CACTUS 119 



in crossing and hybridizing and selective experi- 

 ments, were often forwarded under the supposi- 

 tion that they were specimens of spineless races. 



And many of them were relatively spineless. 



Some of them showed individual slabs that 

 were almost free from spines. 



But without exception these plants, notwith- 

 standing their relative smoothness, would be 

 found to have inconspicuous spicules or bristles, 

 which constituted an armament almost as 

 offensive as the larger spines ; or else would soon 

 demonstrate that their spinelessness was an indi- 

 vidual peculiarity rather than a trait of the race 

 to which they belonged, by developing spines on 

 new slabs. 



Yet the fact that partially thornless Opuntias 

 exist in many regions demonstrates a tendency 

 on the part of this plant to give up its spines 

 partially under some circumstances. 



It shows that in the heredity of the plant there 

 are strains of spinelessness that might presum- 

 ably be utilized by the plant developer in the 

 production of a spineless race. 



In particular it was learned that there is in 

 the Hawaiian Islands cactus that develop speci- 

 mens that are partially thornless when grown on 

 mountainsides in positions absolutely inacces- 

 sible to browsing animals. Also in California, 



