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ear formation, a phase in the development of cereal plants, characterized by the emergence of a head from the sheath of the upper leaf (from the spike in wheat, rye, barley, and other spiked grains and from the panicle in oat, millet, rice, and other paniculate grains). In corn, heading begins with the tasseling of the male inflorescence, or the panicle, on the apex of the stem. Four or five days later the female inflorescence, or the cob, appears on the axil of the leaf. During heading a plant requires more nutrients and a greater amount of moisture. Proper nourishment, moisture, and light promote good development of the inflorescences and simultaneous heading. Prolonged heading results in uneven maturation, making harvesting difficult and leading to crop losses.
(aircraft), the angle between the north direction of a meridian and the projection of an aircraft’s longitudinal axis onto the horizontal plane. The heading is calculated in degrees clockwise from the direction of the meridian. It is called a true heading if it is calculated from the geographic meridian and a magnetic heading if it is calculated from a magnetic meridian. It may be determined by means of magnetic and celestial compasses, directional gyroscopes, or radio compasses. The efficient combination of such instruments into a single compass system eliminates to a considerable extent the deficiencies of separate compass systems, so that it becomes possible to measure headings in all parts of the earth, at any time of day, and under any meteorological conditions.