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TRANSMISSION OF POWER. Engineers. See ; .  TRANS-MISSISSIPPI EXPOSITION. An exposition held in Omaha, Neb., from June 1 to October 31, 1898. The site covered about 200 acres, a mile to the north of the city. The main buildings, which contained the exhibits devoted to Agriculture, Fine Arts, Machinery and Electricity, Manufactures, Mines and Mining, and the United States Government, were grouped around a grand court which extended through the middle of the grounds and surrounded the lagoon or canal which terminated at its west end into a three-lobed lake 400 feet across, at the extreme west end of which was an electric fountain. The grounds were also skillfully improved by the presence of trees, shrubs, and flowering plants until the arid prairie became so changed as to gain the name of Magic City. The buildings were covered with white staff, adorned with intricate carving and classical statuary, resulting in the production of an artistic effect of remarkable beauty. Of special interest among the amusement features was the ethnological gathering of 500 Indians, representing 25 tribes. The total attendance was 2,613,508, and the total receipts $1,924,077.  TRANSPADANE REPUBLIC. A republic formed by Napoleon in 1796 on the south side of the Po, and in 1797 united with the Cispadane Republic, on the north side, to form the (q.v.).  TRANSPIRATION (from Lat. trans, across, through + spirare, to breathe). The evaporation of water from the aerial surfaces of plants. The term is used instead of evaporation, first, because the evaporation is modified by the action of the living organisms; and second, because the development of heat within this organism prevents the complete stoppage of evaporation when the plant is surrounded with a saturated atmosphere. In most land plants, transpiration from the epidermal cells is inconsiderable because such become nearly waterproof by cutinization of the outer walls. The cells bordering the interior air chambers (see ) are saturated with water, and from them it evaporates readily into the air occupying these spaces, whence it finds its way by diffusion through the (q.v.). The rate of transpiration will be determined by the relative humidity of the outer air, temperature, wind, light, etc. Transpiration is unavoidable, because gases must be absorbed from the air (see ); it is necessary, at least to some plants, for cooling; and it is advantageous for the movement of dissolved salts. See .

Since excessive loss of water is one of the greatest dangers to which plants are subject, plants growing in dry regions show a great variety of adaptations to reduce the rate of transpiration and to conserve the moisture which reaches them. (See .) The amount of water transpired varies greatly on account of variation in external conditions and internal structure. A few examples of transpiration under normal conditions will illustrate. In 12 hours on a hot, dry day a sunflower 3.5 feet high, having a leaf area of 5316 square inches, lost 30 ounces of water. The loss of water from 100 square centimeters of leaf surface in 24

hours for the pea was 2.51 grams, for the hop 4.3 grams, for the hemp 9.3 grams. Estimates as to the loss of water during the growing season by the plants of wheat grown on one hectare (about 2.5 acres) equal 1,179,920 liters; and by oats 2,277,760 liters. If all this water could be caught and condensed on the same area it would reach in the first case a depth of nearly 118 millimeters (4⅝ inches), and in the second 228 millimeters (9 inches). A beech tree having 200,000 leaves was estimated to lose between 300 and 400 liters (about 2 barrels) on a hot day.  TRANSPIRATION OF GASES. See .  TRANSPORTATION (in law). See etc.  TRANSPORTATION. The carrying of persons and goods from place to place. The part which transportation plays in the practical life of a community depends most directly upon the complexity of its economic system. Wherever the division of labor and the localization of industry have reached a high degree of development transportation necessarily attains a correspondingly high development. The rise of industry on a great scale and the creation of efficient means of transportation mutually condition each other.

More than a thousand years before our era Phœnician ships were trading in the Mediterranean, and later along the shores of the same sea the Greek cities built up their colonial and trade system. Rome was relatively late in developing maritime traffic, but by the time of the Empire an extensive commercial system had arisen, bringing to Rome the raw produce of Sicily and North Africa, and extending westward even beyond Gibraltar. Ancient land transport was comparatively insignificant. The Greek roads were chiefly to sacred places, such as Delphi, and their economic importance was small. The Roman roads were established for military rather than economic reasons, but they were vastly more extensive. Centring at Rome, they not only stretched through Italy, but (under the Empire) to Constantinople and Asia Minor, along parts of the north coast of Africa, westward to Spain, over the Alps to Gaul, and through Britain. Excellent as these roads often were, their method of construction was wastefully expensive from the modern standpoint.

The return to a more primitive economy in the early Middle Ages meant that for a time transportation should cease to play any important part in the economic life of Europe. The salient points in the story of its gradual revival are the stimulus given by the Crusades to trade with the East, the consequent growth of the Italian cities, and, in the twelfth century, the formation of the great trade league (Hansa) of the North European towns. Although the rise of towns and the establishment of fairs made a certain amount of land or river transport necessary, it was slow, insecure, and costly, and, at least on the Continent, was subject to burdensome and arbitrary tolls. The destruction of the Eastern caravan routes through the Turkish and Mongol invasions gave especial importance to the discovery of an ocean route to the Indies made by Portuguese navigators at the end of the fifteenth