This is because on bright, sunny days with low humidity, transpiration may exceed the rate of water uptake by roots causing the plant to wilt. Loss of turgidity in plant cells also results from moisture stress. This loss of turgidity causes stomata to close, which lowers carbon dioxide uptake by the leaf and reduces dry matter accumulation. When humidity is high, crops can tolerate high temperatures because there is little moisture lost through evaporation (Erdei 1998).

             GROWTH CONSTITUENTS .

             A major limitation to maize grain yields throughout the world is water stress. Clearly determination of kernel number is a dynamic process. Silk growth is inhibited under water stress and a synchrony often limits yield potential. Surface cuticular wax protects silk and leaf tissue from desiccation (Undersander 1987). .

             Corn has a relatively high water requirement. In the central Corn Belt, the amount of water used by the crop, plus that lost by evaporation from the soil surface, generally exceeds normal season rainfall by 3 to 5 inches. This precipitation deficit is offset by water stored in the soil from early season rainfall. During rapid growth in the later vegetative stages of development, a corn plant will use about 0.2 to 0.25 inches of water per day. This may increase to almost 0.33 inches of water per day during pollination. Stress conditions will become evident in the corn plant when 50 percent of the available soil water has been depleted (Schoper 1986). .

             Corn is perhaps the most completely domesticated of all field crops. Its perpetuation for centuries has depended wholly upon the care of man. It cannot exist as a wild plant. Corn plants increase in weight slowly early in the growing season. But as more leaves are exposed to sunlight, the rate of dry matter accumulation gradually increases. Cell division in the leaves occurs at the growing tip of the stem. Leaves enlarge, become green, and increase in dry weight as they emerge from the whorl and are exposed to light.