Gramineae Zea mays L.
Source: Magness et al. 1971
Indians in the Americas were growing corn extensively long before the discovery of these continents by Europeans. Archaeological studies indicate that corn was cultivated in the Americas at least 5600 years ago. The exact origin of corn is unknown as the plant is found only under cultivation. The probable center off origin is the Central American and Mexico region.
The corn plant is a warm weather annual, deep-rooted but requiring abundant moisture for best development. From a seed a single stalk arises that will reach from 2 to near 20 feet depending on kind and growing conditions. This stalk ten-ninates in the tassel or staminate flowers. At the stem nodes are attached the large, smooth leaves which may be more than 2 feet long and 2 inches wide along the mid-point of the stem. At the base of the main stem side shoots or suckers commonly rise, which may produce seeds. The female flowers are borne on a receptacle, termed ear, which arises at a leaf axfl near the mid-point along the stem. Normally one to three or more such ears develop. The flower organs, and later the grain kemels, are enclosed in several layers of papery tissue, termed husks. Strands of "silk", actually the stigmas from the flowers, emerge from the terminals of the ears and husks at the same time the pollen from the terminal tassels is shed. The pollen is wind blown and comes in contact with the emerged silk or stigma. The pollen then germinates and a pollen tube grows down through the silk to the ega cell of the female flower. The male gamete fuses with the egg, and from the fertilized egg the corn seed or kernel develops.
Most varieties of corn require 100 to 140 days from seeding to full ripeness of the kernels though some kinds will ripen in as little as 80 days. The time of pollen shed and fertilization of the egg is a lime after the midpoint of this period.
Corn kernels or seeds vary in size and shape in different kinds and varieties. They may be only an eighth inch long and near round in popcorn to a half inch long and a flattened-cylinder shape in some other kinds. The kernel consists of the following: (1) An outer thin covering which is made up of two layers, an outer pericarp and and inner testa or true seed coat. (2) The endosperm which makes up near 0.66 of the total volume. This consists almost entirely of starch, except in sweet corn. (3) The embryo, the miniature plant structure that develops into a new plant if the seed is planted and grows. The embryo is near one side of the kernel in most kinds rather than in the middle. It contains most of the oil in corn.
Blue-Kerneled Maize from the Southwest United States
Grain corn is further classified commercially into four main types:
(1) Dent corn, when fully ripe, has a pronounced depression or dent at the crown of the kernels. The kernels contain a hard form of starch at the sides and a soft type in the center. This latter starch shrinks as the kernel ripens resulting in the terminal depression. Dent varieties vary in kernel shape from long and narrow to wide and shallow. It is the type mainly grown in this country. (2) Flint corn has the hard starch layer entirely surrounding the outer part of the kernel. Consequently, on drying the kernel shrinks uniformly and does not develop a depressed area. (3) Flour or soft corn kernels contain almost entirely soft starch, with only a very thin layer of hard starch. This type is little grown commercially. (4) Waxy corn is so-called because the endosperm when cut or broken is wax-like in appearance. The starch consists almost entirely of amylopectin, while in ordinary corn the starch is near 30 percent amylose and the remaining 70 percent is amylopectin. Waxy corn is largely used industrially although it is also suitable for food or feed. Acreage of waxy com is small as compared with dent or flint.
Popcorn is characterized by a very high proportion of hard starch. Under heat the moisture in the starch grains expands rapidly resulting in an explosive rupture of the epidermis and the starch grains. Increase in volume after "popping" is 15 to 35 fold, depending on variety. Insufficient moisture in the kernels results in poor popping. Both the plant and ears of popcom are smaller than the grain corns but are otherwise similar.
Pod corn is a curiosity in which each individual kernel is covered by a pod-like growth in addition to the husks enclosing the ear as a whole. It is not grown commercially.
Nearly all the corn now grown in the United States is of hybrid varieties. Seed is obtained by crossing inbred lines which are obtained by self pollination through several generations. This results in reduced vigor and yield but increased uniformity in the inbreds. To produce hybrid seed, two inbreds are planted together and the tassels removed from one before any pollen is shed. Thus kernels on the detasselled variety are from pollen produced on the other inbred line. This restores and increases vigor and is known as a single cross. Two single crosses may be similarly crossed producing what is termed double cross seed. Properly selected and adapted hybrid corn varieties produce higher yields and more uniform plants and ears than the open pollinated varieties formerly used.
About 75 percent of the grain corn produced in the United States is fed to livestock. In hog feeding, whole ears may be used. For other livestock and poultry, and some hog feeding, kernels are removed from the cob by machinery and are often partially ground before feeding. About half of the feeding is done on the farms where the corn is produced.
A little over 10 percent of grain corn grown in the United States is exported either as grain or corn products. From 12 to 15 percent of the crop is processed for starch, corn sugar, syrup, corn oil, corn-oil meal, gluten feed and meal, whiskey, alcohol, and for direct human food in the form of corn flakes, corn meal, hominy and grits.
For silage the corn seed is planted more closely spaced than for grain, to obtain maximum yields. The com is harvested before the kernels ripen, preferably when denting is first apparent on some kernels. At this stage the plant is still green and somewhat succulent. The whole plant is cut near the ground and passed throuch silage cutters either in the field or at the silo or pit. Thus silage is a mixture of all the above-ground plant parts. Corn silage is mainly used for feeding cattle, especially milk cows.