LUTHER BURBANK 



its equivalent, with from .58 per cent, to .72 per 

 cent, of protein, and .96 per cent, to 1.68 per cent, 

 of mineral salts. There is also a very small 

 amount of fat, which like the other nutritious 

 elements is being increased in quantity in some 

 of the newer varieties. The varying amount of 

 these food constituents suggests that the quantity 

 may be considerably increased by selection. 



Of course the same thing is true of the other 

 constituents. No doubt the protein content, for 

 example, may be increased by selective breeding, 

 just as we have seen done in the case of corn. And 

 in general the constituents of the Opuntia slabs 

 that give them food value may doubtless be in- 

 creased by careful combination and selection. 



Hitherto the development of the plant has been 

 carried along the lines of spinelessness and great 

 size and productivity; although, even as the case 

 stands, there has been a considerable improve- 

 ment in the percentage of food constituents. 



In particular the variety Chico shows such 

 advance upon the other varieties, notably the 

 Santa Rosa, in its percentage of mineral salts as 

 to suggest still greater possibilities of development 

 in this direction, although in some respects the 

 Ghico is not an exceptionally good variety. In 

 general the solid content of the Chico variety is 2 

 per cent, greater than that of the Santa Rosa. Such 



[242] 



