Corn kernel may be divided into six major parts: tip cap, hull (pericarp), horny glutinous part (aleurone), horny starchy part (horny endosperm), white starchy endosperm (soft starch) and germ. In corn grain an outer husk surrounds a white or yellow starchy substance. The germ exists at the core of the starchy substance and towards the pointed end. When a corn kernel is cut into two halves the husk, starch and germ can be observed clearly.

High-oil corn differs from normal corn with respect to kernel anatomy and composition. Normal corn has 82% endosperm and 12% germ The germ (including embryo and scutellum) in HOC is proportionately larger than in conventional corn. Normal corn kernel has 8% protein in endosperm and 16% protein in the germ. The germ in HOC has nearly 1 % higher total protein and it also contains higher levels of essential amino acids like lysine, threonine and methionine (Table 1). It is estimated that 80 to 84% of the total 0il is located in the germ, 12% in the aleurone, and 5% in the endosperm. If the tiny piece of germ is cut out and squeezed on a piece of paper, the corn oil may be observed.

The first high-oil corn varieties were selected in 1896 at the University of Illinois. Over the years genetic selection has steadily improved agronomic performance and yield of corn hybrids with higher oil content. Corn kernel oil concentration ranges between 1.2 and 21.3% on weight basis. Commercial hybrids grown in the US corn belt typically contain 4-5% oil. These selections have narrowed the yield gap between high-oil corn and normal corn hybrids, though in general high-oil corn hybrids yield 5-10% lower than normal corn. The corn germ consists of scutellum and embryo. The embryo contains primary axis, plumule, coleoptile, mesocotyl, adventitious and primary roots and the coleorhiza. The scutellum in normal corn makes up about 10-12% of total kernel weight but it contains 83-85% of total kernel oil. Pericarp tip cap and endosperm contain 10-13% of total oil. The scutellum consists of epithelial parenchyma cells and vascular tissues. Oil synthesis takes place in developing scutellum tissue deposits, oil bodies or spherosomes in the parenchyma cells of the scutellum. Immediately after pollination kernel development starts very fast with higher rate of endosperm development as compared to germ. Within 15 days after pollination (DAP) oil can be detected in developing embryos and it continues to increase till 45 DAP and then remains constant to physiological maturity or black layer stage. High-oil inbreds show a high rate of oil accumulation from 15-45 DAP as compared to normal inbreds.