106 LUTHER BURBANK 



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 

 compared with the stem and leaf structure of the 

 plant. So this new illustration of that phe- 

 nomenon 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 the plant, therefore, refuse to conform to the 

 principles of Mendelian segregation, and hit 

 upon a compromise in which the traits of each 

 plant find representation. 



But the flower, somewhat less fixed as to its 

 characteristics, and indeed somewhat less widely 

 divergent in the two species, accepts a compro- 

 mise of a different order, and, under stimulus 



