Tube n.
 1. A hollow cylinder, of any material, used for the conveyance of fluids, and for various other purposes; a pipe.
 2. A telescope. “Glazed optic tube.”
 3. A vessel in animal bodies or plants, which conveys a fluid or other substance.
 4. Bot. The narrow, hollow part of a gamopetalous corolla.
 5. Gun. A priming tube, or friction primer. See under Priming, and Friction.
 6. Steam Boilers A small pipe forming part of the boiler, containing water and surrounded by flame or hot gases, or else surrounded by water and forming a flue for the gases to pass through.
 7. Zool. (a) A more or less cylindrical, and often spiral, case secreted or constructed by many annelids, crustaceans, insects, and other animals, for protection or concealment. See Illust. of Tubeworm. (b) One of the siphons of a bivalve mollusk.
 8. Elec. Railways A tunnel for a tube railway; also (Colloq.), a tube railway; a subway. [Chiefly Eng.]
 Note: In the New York area, the subways running under the Hudson River are sometimes referred to as the tube.
 Capillary tube, a tube of very fine bore. See Capillary.
 Fire tube Steam Boilers, a tube which forms a flue.
 Tube coral. Zool. Same as Tubipore.
 Tube foot Zool., one of the ambulacral suckers of an echinoderm.
 Tube plate, or  Tube sheet Steam Boilers, a flue plate. See under Flue.
 Tube pouch Mil., a pouch containing priming tubes.
 Tube spinner Zool., any one of various species of spiders that construct tubelike webs. They belong to Tegenaria, Agelena, and allied genera.
 Water tube Steam Boilers, a tube containing water and surrounded by flame or hot gases.


 Flue n.
 1. An inclosed passage way for establishing and directing a current of air, gases, etc.; an air passage; esp.: (a) A compartment or division of a chimney for conveying flame and smoke to the outer air. (b) A passage way for conducting a current of fresh, foul, or heated air from one place to another. (c) Steam Boiler A pipe or passage for conveying flame and hot gases through surrounding water in a boiler; -- distinguished from a tube which holds water and is surrounded by fire. Small flues are called fire tubes or simply tubes.
 2. In an organ flue pipe, the opening between the lower lip and the languet.
 Flue boiler. See under Boiler.
 Flue bridge, the separating low wall between the flues and the laboratory of a reverberatory furnace.
 Flue plate Steam Boiler, a plate to which the ends of the flues are fastened; -- called also flue sheet, tube sheet, and tube plate.
 Flue surface Steam Boiler, the aggregate surface of flues exposed to flame or the hot gases.