ORIGIN, CLASSIFICATION, VARIETIES OF CORN 179 



that the kernels "turn inside out " when heated, and by the 

 small size of the kernels and ears. There is also an exces- 

 sive proportion of the corneous endosperm, which gives the 

 property of "popping." An explanation of the property 

 of "popping" lies in the fact that heat causes the explosion 

 of contained moisture, and the endosperm being so dense 

 that the expansion cannot be taken up on the inside,' the 

 endosperm is caused to evert about the embryo and 

 hull, forming a white fluffy mass. In kernels possessing 



Fig. 32., — An ear of White Pearl pop-corn. 



ari excess of white endosperm, the moisture in the corneous 

 portion explodes without everting the endosperm. 



Although many varieties of pop-corn exist they easily 

 fall into two groups, namely, rice pop-corn, "in which the 

 kernels are pointed at the top, and pearl pop-corn, in which 

 the kernels are rounded at the top much as in flint corn. 

 Ears of pop-corn vary in length from IJ/^ or 2 inches in 

 Tom Thumb to 6 or 7 inches in certain varieties of the 

 pearl group. 



220. Zea Mays indurata, the flint coms (Fig. 33). — 

 Characterized by the inclosure of the starchy endosperm 

 in a corneous endosperm. This outer arrangement of the 

 hard part of the endosperm prevents denting, although 

 a slight dent is sometimes visible owing to the fact that the 

 layer of corneous endosperm is thin on the ' top of the 



