Spaced groups of component filter portions for forming into composite filter rods are assembled by retarding selected portions of the stream by means of transversely-applied suction. The suction means may include a rotary valve operable periodically to connect a suction manifold to a suction outlet adjacent the path of the stream. The stream may be formed and conveyed at an endless band which receives the portions indirectly from a hopper via a fluted drum. The hopper may incorporate an additional feed band which agitates the rods in the hopper to ensure that each flute of the fluted drum receives a rod.