THE CACTUS 149 



The slabs during the period of their best de- 

 velopment, when they would ordinarily be used 

 for forage, contain, according to chemical analy- 

 sis, from 2.71 per cent to 4.6 per cent of starch 

 and 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 nutri- 

 tious 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 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 now stands, there has been a consider- 

 able improvement in the percentage of food 

 constituents. 



Even at the present time, however, the slabs 

 of the Opuntias furnish fodder of highly nutri- 



