.114 PLANT-BREEDING 



species. It embraces seven types which are different enough 

 to be considered by some authors as the equivalent of sys- 

 tematic species. Each of these groups includes a number 

 of varieties or sub-races, and these, in their turn, are by no 

 means uniform, but offer to the experienced eye an utter 

 chaos of indi\idual variations. 



The signihcance of the main types and their most evi- 

 dent varieties is nowadays fairly well established, but it 

 is the almost inexhaustible individual variability within the 

 varieties that gives the material for selection. 



The main types are six in number, viz. : The pod corns, 

 the pop corns, the flint corns, the dent corns, the soft corns, 

 and the sweet corns. In the pod corns or Zea Mays tuni- 

 cata the kernels of the ear are enclosed in husks, constitu- 

 ting together a pod for each single kernel. This is the form 

 wliich was assumed by Darwin to be the nearest relative of 

 the hypothetical ancestors of the whole group, since corn is 

 the only species in the family of the grains, which possesses 

 naked kernels. 



The pop corn is easily recognized by the small size of 

 the kernels and ear and by the excessive proportion of the 

 horny or corneous endosperm, which, in the best varieties, is 

 so well developed that it wholly excludes the starchy tissues. 

 Tliis gives the property of popping, by which process the 

 kernel is burst and the contents turned inside out. The 

 rice pop corns, with pointed kernels, are among the best- 

 known races of this group. 



The flint corns have a well- developed starchy tissue en- 

 closed by the horny endosperm. This latter varies in thick- 

 ness with the varieties and causes the kernels to become too 

 hard when dry for cattle to eat them without their being 

 ground. Thence, the Latin name "indurata. " 



The dent corns, Zea Mays indentata, are easily recog- 

 nized by the indentation on their outer surface. This de- 



