Kernels. — The caryopses or kernels of corn (Fig. 596), re sulting from the act of fertili zation, are arranged in even numbered rows on the fleshy axis, or, cob, surrounded by the husk. Each husk represents the sheathing leaf base and the outer ones are usually tipped by a green, rudimentary leaf-blade, which occasionally displays a ligule: The outer, innermost husk is two-keeled, like a sled with runners, and thus it accommo dates itself to the flattened or hollowed-out stem surface. Occasionally smaller ears are enclosed by the outer husks, so that the ear together with the husks is to be regarded as a short, axillary, branch bearing reduced leaves and flowers.
Each caryopsis has two distinct coats, viz., the ovarian wall and the seed-coats. On microscopic section, the cell layers composing the ovarian wall, or pericarp, and the extremely thin seed-coats are distinctly visible. The reserve food in corn is horny proteinaceous material and mealy starch, while the embryo itself contains the largest amount of oil. The proteinaceous and starchy reserve foods comprise the albumen, which touches the embryo on the whole of one side, where the scutellum is found. The corn embryo, chit or germ, consists of the radicle surrounded by a root-sheath, or coleo rhiza, a short hypocotyl from which arises the suck ing organ, or scutellum, and a single cotyledon that surrounds several tightly-rolled plumular leaves. The epidermal cells of the scutellum secrete an enzyme which transforms the reserve food into a usable form when the embryo begins to grow.
In germination, the radicle protrudes first by breaking its way through the coleorhiza, which remains as a circular collar about its upper part, and then the plumule elongates. The cotyledon re mains yellowish green and membranous, while the leaves enwrapped by it elongate and assume a bright green color. Coincident with this develop ment of the plumule, a considerable number of secondary adventitious roots arise, so that the primary root soon loses its identity.
Classification of specks-groups or "agricultural species." Several well-marked agricultural races of Indian corn may be distinguished. The asterisk (*) indi cates Mays understood. The classification is that of Dr. E. L. Sturtevant: (1) Zea canine, Watson. Maiz de Coyote, a re puted wild form from Mexico. The writer has abun dantly proved that this so-called wild species is a hybrid of the fourth or fifth generation produced by crossing teosinte and the black Mexican corn.
(2) Zca * tu n kola. Pod Corn. In this group each kernel is inclosed in a pod, or husks surround it, and the ear thus formed is inclosed in husks. Originally it was probably derived from Argentina in South America. (Fig. 598.) (3) Zea * ererta. Pop Corn. This species-group is characterized by the excessive proportion of the corneous endosperm and the small size of the ear and kernel. The best varieties have the corneous endosperm throughout, which gives the property of popping. Probably cultivated by the Indians.
(4) Zen * indurata. Flint Corn. A species-group recognized by the occurrence of a starchy endo sperm, inclosed in a corneous endosperm, which varies in thickness in different varieties. First mentioned by Cartier in 1535 and Heriot in 1588.
(5) Zen * indentata. Dent Corn. A group recog nized by the presence of corneous endosperm at the sides of the kernel, the starchy reserve food ex tending to the summit. By the drying and shrinkage of the starchy endosperm, an indentation is formed. Cultivated as poketawes by the Powhatan Indians.
(6) Zea * aulglacca. Soft Corn. These corns are recognized by the absence of a corneous reserve food. The mummy corns of Chili and Peru belong to this class.
(7) Zen * saeeharata. Sweet Corn. A well-defined species-group characterized by the translucent, horny appearance of the kernels and their more or less crinkled, wrinkled or shriveled condition. The first sweet corn cultivated in America was derived from the Susquehanna Indians in 1779 by Captain Richard Begnall, who accompanied General Sullivan on his expedition to subdue the Six Nations.
(S) Zen * anzylea-saecharata. Starchy-sweet Corn. The external appearance of the kernel is that of a sweet corn, but examination shows that the lower half of the kernel is starchy, the upper half horny and translucent. May it not be due to xenia ? This species is based on three varieties found in the San Pedro Indian collection of Dr. Palmer, sent to Dr. E. L. Sturtevant in 1886.
Maize is exceedingly variable in every part. Therefore it adapts itself to great numbers of uses and to wide ranges of territory. Some of the forms of it are shown in the half-tone plate and also in Figs. 597-613.