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The xylem vessel constitutes part of the vascular ( bundle, package, tube, vein ) and is formed of ( dead cell remnants, living cells, extracellular matrix, collagen ) joined end-to-end. The cell ( walls, cytoplasm, surface membranes ) are fortified with ( lignin, lining, cholesterol, starch ) to make the xylem ( waterproof, water soluble, semi-permeable, an active transporter ) and ( strong, flexible, bendy, variable ). The cell walls at the ends of the cells ( break down, fuse, swell, bud off ), giving rise to a long, hollow tube.