convenient for purposes of description. The principal field varieties which are grown are the flint corn, Zea indurata, and the dent corn, Zea indentata.
POPCORN.
This variety of maize is used very largely in the United States as a delicacy, and with sugar and cream as a dessert. It is a hard, small-grained variety which has the property, when heated, of exploding with a very great enlargement of the starch grain, producing a soft and very delicate edible material which is highly prized.
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Fig. 25.—Section of Popcorn in First Stage of Popping, Showing Partially Expanded Starch Grains and Ruptured Cell Walls. × 150.—(Courtesy of Bureau of Chemistry.)
In the raw popcorn the starch grains are packed together very closely within the cells. When popping begins there is an expanding of the starch grains, producing a cavity nearly circular in form in each grain. This causes a rupturing of the cell walls, though fragments are plainly visible in the early stages. In the fully expanded or popped kernel the starch grains have expanded until each is about half or two-thirds as large as the original cells of the endosperm. The cell walls in this stage are practically obliterated as far as detecting in a section is concerned. The exploding of the starch grains is influenced by the water content of the kernel. It must not be too
