170 LUTHER BURBANK 



tent. Their foliage value is not quite what it 

 would be if the protein content could be in- 

 creased. And there is no reason to doubt that 

 such increase may be possible through selective 

 breeding. Already the developed spineless opun- 

 tias exceed all other plants in their capacity 

 to produce an enormous quantity of forage. 

 Through selective breeding their preeminence 

 may be still further advanced in that each indi- 

 vidual slab may be given enhanced food value. 

 And the qualities of other useful chemical sub- 

 stances in the cactus may similarly be increased 

 in selective varieties. 



Heretofore the development of the 

 cactus has been along the lines of 

 spinelessness, size, and productiv- 

 ity; the future will see a marked 

 improvement in the percentage of 

 its food constituents, especially in 

 its fruits. 



