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 wet nor too dry; about 10 or 12 percent is the proper content of moisture. These changes are beautifully shown in the accompanying microphotographs, Figs. 24, 25, and 26, by Mr. Howard, of the Bureau of Chemistry. [Illustration: FIG. 26.--SECTION OF FULLY POPPED POPCORN. × 150.--(_Courtesy of Bureau of Chemistry._) The fully expanded starch grains are nearly half as large as the original cells in which they were contained.] SWEET CORN. This is a variety of maize which develops a high sugar content and is eaten while the starch is yet soft, in other words, in an unripe state. It is a food product of immense importance in the United States, although almost unknown in Europe. The content of sugar varies from 5 to 8 percent in the fresh, soft kernel. The sugar which is present in the kernel rapidly disappears after the husking or removal from the stalk. In order to secure the maximum sweetness the corn should be cooked and eaten as soon as possible after removal from the stalk. Where it is not possible to do this it should be placed in cold storage after removal from the stalk and remain unhusked until it is ready for cooking. Green corn is universally eaten hot. It is usually cooked by boiling in water, although it may also be roasted before the fire. It has a high food value, and the composition of the grains of fresh, soft, green corn is shown in the following table: _Composition of Fresh Green Indian Corn_: Moisture, 73.00 percent Starch, 13.50 „ Sugars, 6.00 „ Protein, 5.00 „ Crude fiber, 1.20 „ Ash, .70 „ Fat, .60 „ =Maize Proteins.=--The proteins of maize are composed principally of two zeins. The two forms are differentiated by their behavior toward alcohol. The first form constitutes the zein soluble in alcohol and the second the zein insoluble in alcohol. There are two other proteins in maize existing in small quantities which have been named myosin and vitellin, respectively. There is also a third unnamed variety and small quantities of albumin.