transpiration (trans pir ash on)

[F.tran spiration = Sp. Sp. trans pir a cion, traspiracion Pg. transpiração = It. traspirazione, I never neede other powdering to my hair, which dos certainely greately prejudice transpiration by filling up or lying heavy upon the pores. Evelyn , To Doctor Beale. 2. In bot., the exhalation of watery vapor from the surface of the leaves of plants. A great part of the water which serves as the vehicle of the nutritious substances contained in the sap is disposed of by transpiration. When thus given out it sometimes appears in the form of extremely small drops at the tip of the leaf, and especially at the extremities of the nerves. - Pulmonary transpiration, the exhalation of watery vapor from the blood circulating through the lungs. It may be made evident by breathing on a cold reflecting surface. - Transpiration of gases, the motion of gases through a capillary tube under pre ure. The rate of motion varies with the composition of the gas, but bears a constant relation not coinciding with density, diffusion, or any other known property. The velocity depends not simply on the friction of the gas against the surface of the tube, but much more on the friction of the gas-particles against each other, and the transfer of momentum which thus results. A comparison of the velocity of transpiration with that of effusion has led to important conclusions in regard to molecular magnitudes. - Transpiration of liquids, the motion of liquids through minute orifices or capillary tubes under pre ure. The rates of such motions are greatly increased by heat.