the height of a continuous tobacco stream between a first side which is supported by a conveyor and an uneven second side is monitored by an opto - electrical level detector which directs a row of parallel light rays transversely across the stream and has a battery of photosensitive elements at different distances from the first side of the stream so that each element produces a signal in response to impingement of a different light ray upon its photosensitive surface . the number of elements which generate signals is indicative of the height of the stream portion advancing past the level detector . such signals can be utilized to adjust a trimming device which removes the surplus at the second side of the stream before the thus equalized stream enters a wrapping mechanism to be converted into a cigarette rod which is thereupon severed to yield discrete cigarettes .