Abstract: A stream of air is circulated by a blower along an endless path a portion of which is defined by an upright duct having an air inlet at its lower end, an air outlet at its upper end, and an inlet for comminuted tobacco particles intermediate its air inlet and air outlet. The particles of tobacco which are admitted into the duct are classified according to weight by the ascending air stream which advances satisfactory particles toward the outlet where the particles are attracted to a driven foraminous belt conveyor to form a growing tobacco stream. The air inlet of the duct contains a rotary impeller which distributes the inflowing air across the full width of the duct so that the thus formed air stream ensures a predictable classifying action and the formation of a homogeneous shower of satisfactory particles which are advanced toward the stream growing zone.