=Varieties.=--There are many distinct varieties of Indian corn. Sturtevant has published a description of several hundred. These varieties are classified under various subspecies. The polymorphic species, _Zea mays_, according to Sturtevant, can be divided into a number of groups which, on account of their well defined and persistent characters, may be considered as presenting specific claims and may properly receive specific nomenclature. The grouping adopted is founded upon the internal structure of the kernel for cultivated varieties, and the presence of a husk to the kernel in the assumed aboriginal form. Hence Sturtevant offers the names _Zea tunicata_ for the husk-kernel forms, _Zea everta_ for the popcorn, _Zea indurata_ for the flint corns, _Zea indentata_ for the dent corns, _Zea amylacea_ for the soft corns, and _Zea saccharata_ for the sweet corns. [Illustration: FIG. 24.--SECTION OF RAW POPCORN. × 150.--(_Courtesy of Bureau of Chemistry._) Shows cells with the small angular starch grains closely packed together within them.] Argument in favor of the specific claims for these groups is based primarily on the convenience thus attained; secondarily, on the absence or rarity of intermediate or connecting forms, so far as present data extend, and also on the antiquity of the separation. It seems almost certain that in the order of evolution (excluding from consideration the puzzling sweet corn group) progress has been from the pops, through the flints and the dents, to the softs. Certainly the soft corns in some of their varieties present a kernel that is larger, softer, and less fitted to the struggle with natural conditions than is the kernel from any of the other groups. Yet soft corns are the prevailing form in the mummy burials of Peru and of our Southwestern states. The popcorn, on the contrary, has stronger regerminative powers than have the other groups, is better fitted to contend against natural vicissitudes, and is the kind that has been reported as found growing wild in Mexico under the name of Coyote corn, _Zea canina_ Watts. Some of these subdivisions may not be accepted by botanists, but they are 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. [Illustration: 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._)]