E52 Proceedings of Indiana Academy of Science 
hexagonal, closely-arranged starch grains, only a small amount of col- 
loid being necessary to fill the interstices completely; the latter had 
small, rounded, loosely-arranged starch grains, and the relatively large 
amount of protein-bearing material was not sufficient to fill the spaces 
and produce a flinty texture. The difference between the two condi- 
tions is not wholly one of heredity, the weather conditions attendant 
upon maturity, and doubtless the chemical constitution of the soil, being 
determining factors. 
Structure of the Starch Grain.—Kraemer’s theory that the ability 
to pop is dependent upon the minute structure of the starch grain, is 
not readily substantiated. The extremes that he notes between pop- 
ping and non-popping varieties in this respect can all be found in good 
popping varieties if enough samples are examined. 
The “Puffed” Cereals.—Contrary to the opinion expressed by Carr 
and Ripley (p. 261), there is good evidence that in the manufacture 
of the “puffed” cereals exactly the same principle is involved as in 
the popping of corn, man having provided what nature omitted. The 
grain, containing a proper amount of moisture, is enclosed in an air- 
tight metal drum and heated until the optimum temperature and pres- 
sure have been reached. Then, by suddenly opening the drum, the 
pressure outside each grain of the cereal is released, and each starch 
grain explodes because of the internal pressure of the steam. 
SUMMARY. 
The popping of a grain of corn is an explosion due to the expan- 
sion, under pressure, of moisture contained in the starch grains. Until 
the instant of the explosion, this force is confined by the colloidal 
matrix in which the starch grains are embedded. Neither air nor any 
volatile oil is in any way concerned with the process as the expansive 
medium. 
As a result of popping, there is hydrolysis of much of the starch, 
a loss of moisture, and the obliteration of all cellular structure in the 
endosperm. 
Except to aid slightly in confining the pressure, neither the embryo 
nor the hull (pericarp) of the grain plays any part in the process. 
Maximum, minimum, and optimum moisture contents are indicated, 
but the range is wide. 
The flinty texture of the endosperm is an accurate index to pop- 
ping qualities. Hardness of the endosperm is due to nitrogenous ma- 
terial filling the interstices between the starch grains; but, because of 
variation in the size, shape, and proximity of the starch grains,—and 
consequent variation in the relative amount of material necessary to 
fill the interstices,—popping quality is not in direct proportion to pro- 
tein content. 
The difference between popping and non-popping varieties is wholly 
one of hardness of endosperm. Popping is not in any way dependent 
upon the minute structure of the starch grain. Non-popping varieties 
may be made to pop if they are heated to the proper temperature under 
pressure and the pressure suddenly released. 
