ON THE SPINELESS CACTUS 



nothing of that tendency to racial variation in the 

 second generation that marks hybrids in general, 

 and that, as will appear in a moment, marks the 

 hybrids of the other cactuses very conspicuously. 



But there is an added element of great interest 

 in the fact that the blossoms of the new hybrid 

 so markedly differs from the flowers of either par- 

 ent and so conspicuously excels either of them in 

 size and beauty. 



It would seem that the floral envelope occupies 

 a position in the hereditary scale somewhat dif- 

 ferent from that of the main stem of the plant. And 

 this is perhaps not strange, when we reflect that 

 the flower is a relatively recent development in 

 the history of plant life. 



We have already noted that flowering plants 

 are of comparatively recent origin, geologically 

 speaking. 



We have seen evidences here and there of the 

 relative adaptability of the floral envelope as com- 

 pared with the stem and leaf structure of the plant. 

 So this new illustration of that phenomenon need 

 not surprise us, however much it may interest us. 

 It would appear, if we may interpret the phe- 

 nomena just presented, that the giant and dwarf 

 Opuntias have diverged so widely that they are 

 practically at the limits of affinity that permit 

 crossbreeding. The stems and main structures of 



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