Parts of a Maize Seed

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Corn kernels have a complex interior make-up.
Corn kernels have a complex interior make-up. (Image: Jupiterimages/liquidlibrary/Getty Images)

Maize, or corn, produces seeds called kernels. A kernel is referred to as a caryopsis, a dry seed-like fruit of a cereal grass, in botanical definition. Starch is the major carbohydrate storage product in a kernel. Each kernel is 70 to 72 percent starch by dry weight. According to the Iowa State University Extension, kernel size matters, as smaller seeds often lead to lower germination rates and less vigorous plants.

Pericarp

The pericarp, or seed coat, is the tissue that surrounds the seed, protecting its contents. Other names for the pericarp include husk, hull or bran. The pericarp develops from the ovary wall of the flower. It is made up of the epidermis, mesocarp, cross cells, tube cells and seed coat. The pericarp is formed of carbohydrates, particularly fiber or cellulose. The pericarp is resistant to water and deters insect pests from reaching the inner kernel.

Endosperm

The endosperm carries the food energy for the plant-to-be in the form of starch. At 83 percent of the kernel weight, the endosperm makes up majority of the kernel weight. The endosperm contains the soft endosperm, the horny endosperm and aleurone protein. The hard endosperm has tightly packed starch, while the soft endosperm has loose starch. When corn dries, it is loss of moisture in the soft endosperm that forms the dent in the top of the kernel. The endosperm is triploid, which means it contains three complete sets of chromosomes.

Embryo

The embryo, or germ, is an immature plant, appearing on the indented side of the kernel. This part of the kernel is alive and carries the genetic information for the kernel. The embryo contains the plumule, the seed leaf or cotyledon, the hypocotyl, the radicle or embryonic root and the coleorhiza, or covering of the embryonic root. The plumule includes the epicotyl -- the stem of the embryo -- and coleoptile, which protects the shoot tip and embryonic leaves. The embryo carries vitamins and minerals for the kernel. Approximately 25 percent of the germ is made up of corn oil.

Tip Cap

The kernel tip or tip cap is the point at which the kernel attaches to the cob. The tip cap is made up of dead tissue. The pericarp does not cover this part of the kernel. The tip cap protects the end of the germ.

Ripening

Corn kernels undergo several stages during ripening. During the first stage, or blister stage, the kernels are white, fluid-filled structures. This stage occurs 10 to 14 days after silking. At the milk stage, kernels develop a yellow color and fill with milky fluid. Upon reaching the dough stage, the kernel begins to firm from the top down and solidify inside. During the dent stage, a dent forms and a starch layer appears within the kernel, and at half maturity, the hard starch layer extends approximately halfway down the kernel. At the black layer stage, the hard starch reaches the cob and the kernels reach their maximum dry weight.

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